阅读说明：本技术 用于形成分级纤锌矿iii族氮化物合金层的方法 (Method for forming a graded wurtzite group III nitride alloy layer ) 是由 李晓航 刘开锴 于 2018-12-04 设计创作，主要内容包括：一种用于在第二层上形成包括包含纤锌矿III族氮化物合金的分级纤锌矿III族氮化物合金层的半导体器件的方法。基于半导体器件的预期功能选择针对分级纤锌矿III族氮化物合金层的极化掺杂浓度分布。基于所选择的针对分级纤锌矿III族氮化物合金层的极化掺杂浓度分布,确定分级纤锌矿III族氮化物合金层的组分-极化变化率和分级纤锌矿III族氮化物合金层的分级速度。组分-极化变化率和分级速度均基于纤锌矿III族氮化物合金的第一元素和第二元素的组分。使用所确定的组分-极化变化率和分级速度,基于分级纤锌矿III族氮化物合金层中距离第二层的当前位置来调整纤锌矿III族氮化物合金的第一III族氮化物元素和第二III族氮化物元素的组分,以在第二层上形成具有所选择的极化掺杂浓度分布的分级纤锌矿III族氮化物合金层。(A method for forming a semiconductor device comprising a graded wurtzite group III nitride alloy layer comprising a wurtzite group III nitride alloy on a second layer. The polarization doping concentration profile for the graded wurtzite group III nitride alloy layer is selected based on the intended function of the semiconductor device. Determining a composition-polarization rate of change of the graded wurtzite group III nitride alloy layer and a grading rate of the graded wurtzite group III nitride alloy layer based on the selected polarization doping concentration profile for the graded wurtzite group III nitride alloy layer. The composition-polarization change rate and the grading rate are both based on the composition of the first element and the second element of the wurtzite group III nitride alloy. Using the determined composition-polarization rate of change and the grading rate, the compositions of the first group III nitride element and the second group III nitride element of the wurtzite group III nitride alloy are adjusted based on a current position in the graded wurtzite group III nitride alloy layer from the second layer to form a graded wurtzite group III nitride alloy layer having the selected polarization doping concentration profile on the second layer.)

1. A method for forming a semiconductor device (200) comprising a graded wurtzite group III nitride alloy layer (210) comprising a wurtzite group III nitride alloy on a second layer (205), the method comprising:

selecting (105) a polarization doping concentration profile of a graded wurtzite group III nitride alloy layer (210) based on an intended function of the semiconductor device (200);

determining (110) a composition-polarization rate of change of the graded wurtzite group III nitride alloy layer (210) and a grading rate of the graded wurtzite group III nitride alloy layer (210) based on the polarized doping concentration profile of the selected graded wurtzite group III nitride alloy layer (210), wherein the composition-polarization rate of change and the grading rate are both based on the composition of the first element and the second element of the wurtzite group III nitride alloy; and

forming (115) a graded wurtzite group III nitride alloy layer (210) having a selected polarization doping concentration profile on the second layer (205) based on adjusting the composition of the first group III nitride element and the second group III nitride element of the graded wurtzite group III nitride alloy layer (210) based on a current position in the graded wurtzite group III nitride alloy layer (210) from the second layer (205) using the determined composition-polarization rate of change and grading speed.

2. The method of claim 1, wherein the polarization doping concentration profile is determined using a product of a composition-polarization rate of change of the graded wurtzite group III nitride alloy layer and a grading rate of the graded wurtzite group III nitride alloy layer.

3. The method of claim 2, wherein the method is based onTo determine the classified wurtzite IIA composition-polarization rate of change of the group I nitride alloy layer, wherein dP is a change in polarization and dx is a change in composition of the graded wurtzite group III nitride alloy layer.

4. The method of claim 3, wherein the method is based onDetermining the grading rate, wherein dx is a change in composition of the graded wurtzite group III nitride alloy layer and dl is a change in distance in a thickness direction of the graded wurtzite group III nitride alloy layer.

5. The method of claim 4, wherein the graded wurtzite group III nitride alloy layer comprises a first group III nitride having a first concentration and a second group III nitride having a second concentration, wherein the forming of the graded wurtzite group III nitride alloy layer comprises:

changing a relative amount of the first concentration of the first group III nitride and the second concentration of the second group III nitride based on a change in distance from the second layer.

6. The method of claim 1, wherein the formed graded wurtzite group III nitride alloy layer is a doped layer without purposely adding other elements to the graded wurtzite group III nitride alloy layer.

7. The method of claim 1, wherein

The polarized doping concentration of the determined polarized doping concentration profile is fixed over the thickness of the formed graded wurtzite group III nitride alloy layer,

the determined composition-polarization rate of change is variable over the thickness of the formed graded wurtzite group III nitride alloy layer, and

the determined grading rate is variable over the thickness of the formed graded wurtzite group III nitride alloy layer.

8. The method of claim 1, wherein

The polarized doping concentration of the determined polarized doping concentration profile is fixed over the thickness of the formed graded wurtzite group III nitride alloy layer,

the determined composition-polarization rate of change is variable over the thickness of the formed graded wurtzite group III nitride alloy layer, and

the determined grading rate is fixed over the thickness of the formed graded wurtzite group III nitride alloy layer.

9. The method of claim 1, wherein

The polarized doping concentration of the determined polarized doping concentration profile is variable over the thickness of the formed graded wurtzite group III nitride alloy layer,

the determined composition-polarization rate of change is variable over the thickness of the formed graded wurtzite group III nitride alloy layer, and

the determined grading rate is fixed or variable over the thickness of the formed graded wurtzite group III nitride alloy layer depending on the determined variable polarization doping concentration and the determined variable composition-to-polarization rate of change.

10. The method of claim 1, wherein the second layer is a gallium nitride substrate or an aluminum nitride substrate.

11. A method for forming a semiconductor device (200) comprising a graded wurtzite group III nitride alloy layer (210) comprising a wurtzite group III nitride alloy on a second layer (205), the method comprising:

selecting (405) a range of polarization doping concentration profiles for a graded wurtzite group III nitride alloy layer (210) based on an intended function of the semiconductor device;

determining (410) a range of component-polarization rates of change of the graded wurtzite group III nitride alloy layer (210) and a range of grading rates of the graded wurtzite group III nitride alloy layer (210) based on the selected range of polarization doping concentration profile of the graded wurtzite group III nitride alloy layer (210), wherein the range of component-polarization rates and the range of grading rates are both based on the components of the first and second elements of the wurtzite group III nitride alloy; and

adjusting the composition of the first group III nitride element and the second group III nitride element of the group III nitride alloy based on the current position in the graded wurtzite group III nitride alloy layer (210) from the second layer (205) using the determined composition-polarization rate of change within the range of composition-polarization rates and the determined grading speed within the range of grading speeds, forming (415) a graded wurtzite group III nitride alloy layer (210) on the second layer (205) having a polarization doping concentration profile within the selected range of polarization doping concentration profiles.

12. The method of claim 11, wherein the range of the polarization doping concentration profile is determined using a product of a rate of change of composition-polarization of the graded wurtzite group III nitride alloy layer and a grading rate of the graded wurtzite group III nitride alloy layer.

13. The method of claim 12, wherein the method is based onTo determine a range of compositional-polarization rates of the graded wurtzite group III nitride alloy layer, wherein dP is the change in polarization and dx is the change in composition of the graded wurtzite group III nitride alloy layer.

14. The method of claim 13, wherein the method is based onTo determine the range of grading rates, wherein dx is a fraction of the wurtzite group III nitride alloy layerThe change in composition and dl is the change in distance in the thickness direction of the graded wurtzite group III nitride alloy layer.

15. The method of claim 14, wherein the graded wurtzite group III nitride alloy layer comprises a first group III nitride having a first concentration and a second group III nitride having a second concentration, wherein the forming of the graded wurtzite group III nitride alloy layer comprises:

changing a relative amount of the first concentration of the first group III nitride and the second concentration of the second group III nitride based on a change in distance in a thickness direction of the graded wurtzite group III nitride alloy layer.

16. A method for forming a semiconductor device (200) comprising a graded wurtzite group III nitride alloy layer (210) on a second layer (205), the method comprising:

determining (505) a polarization doping concentration profile of the graded wurtzite group III nitride alloy layer (210) based on a product of a composition-polarization rate of change of the graded wurtzite group III nitride alloy layer and a grading rate of the graded wurtzite group III nitride alloy layer;

determining (510) a thickness (T) of a graded wurtzite group III nitride alloy layer (210), wherein the graded wurtzite group III nitride alloy layer (210) comprises a first group III nitride element and a second group III nitride element;

determining (515) initial amounts of a first group III nitride element and a second group III nitride element for forming a graded wurtzite group III nitride alloy layer (210);

determining (520) final amounts of first and second group-Ill nitride elements for forming a graded wurtzite group-Ill nitride alloy layer (210) based on the polarization doping concentration profile, thickness (T), and initial amounts of the first and second group-Ill nitride elements;

determining (525) initial amounts of adjusting the first group-Ill nitride element and the second group-Ill nitride element based on the final amounts of the first group-Ill nitride element and the second group-Ill nitride element;

determining (535) adjusted initial amounts of the first group Ill-nitride element and the second group Ill-nitride element;

determining (540) adjusted final amounts of first and second group-Ill nitride elements for forming a graded wurtzite group-Ill nitride alloy layer (210) based on the polarization doping concentration profile, thickness (T), and adjusted initial amounts of the first and second group-Ill nitride elements; and

forming (545) a graded wurtzite group III nitride alloy layer (210) such that a portion of the graded wurtzite group III nitride alloy layer (210) adjacent to the second layer (205) has an adjusted initial amount of the first group III nitride element and the second group III nitride element and a portion of the graded wurtzite group III nitride alloy layer (210) furthest from the second layer (205) has an adjusted final amount of the first group III nitride element and the second group III nitride element.

17. The method of claim 16, wherein the method is based onTo determine a composition-polarization change rate of the graded wurtzite group III nitride alloy layer, wherein dP is a change in polarization and dx is a change in composition of the graded wurtzite group III nitride alloy layer.

18. The method of claim 17, based onDetermining the grading rate, wherein dx is a change in composition of the graded wurtzite group III nitride alloy layer and dl is a change in distance in a thickness direction of the graded wurtzite group III nitride alloy layer.

19. The method of claim 18, wherein the graded wurtzite group III nitride alloy layer comprises a first group III nitride having a first concentration and a second group III nitride having a second concentration, wherein the forming of the graded wurtzite group III nitride alloy layer comprises:

changing a relative amount of the first concentration of the first group III nitride and the second concentration of the second group III nitride based on a change in distance from the second layer.

20. The method of claim 16, wherein the graded wurtzite group III nitride alloy layer is formed using metal organic vapor deposition, molecular beam epitaxy, or high temperature post deposition annealing.

Technical Field

Embodiments of the disclosed subject matter generally relate to methods for forming graded wurtzite group III nitride alloy layers by controlling the grading of wurtzite group III nitride elements during the formation of graded layers such that the graded wurtzite group III nitride semiconductor layers have a particular polarization doping concentration profile.

Background

Disclosure of Invention

According to an embodiment, a method is provided for forming a semiconductor device including a graded wurtzite group III nitride alloy layer including a wurtzite group III nitride alloy on a second layer. The polarization doping concentration profile of the graded wurtzite group III nitride alloy layer is selected based on the intended function of the semiconductor device. Determining a composition-polarization change rate of the graded wurtzite group III nitride alloy layer and a grading rate of the graded wurtzite group III nitride alloy layer based on the polarization doping concentration distribution of the selected graded wurtzite group III nitride alloy layer. The composition-polarization change rate and the grading rate are both based on the composition of the first element and the second element of the wurtzite group III nitride alloy. Using the determined composition-polarization rate of change and the grading rate, the compositions of the first group III nitride element and the second group III nitride element of the wurtzite group III nitride alloy are adjusted based on a current position in the graded wurtzite group III nitride alloy layer from the second layer, forming a graded wurtzite group III nitride alloy layer having the selected polarization doping concentration profile on the second layer.

In accordance with another embodiment, a method is provided for forming a semiconductor device including a graded wurtzite group III nitride alloy layer including a wurtzite group III nitride alloy on a second layer. The range of the polarization doping concentration profile for the graded wurtzite group III nitride alloy layer is selected based on the intended function of the semiconductor device. Based on the selected range of polarization doping concentration distribution for the graded wurtzite group III nitride alloy layer, a range of composition-polarization change rate of the graded wurtzite group III nitride alloy layer and a range of grading speed of the graded wurtzite group III nitride alloy layer are determined. The range of composition-polarization change rates and the range of classification rates are based on the composition of the first element and the second element of the wurtzite group III nitride alloy. Adjusting the composition of the first group III nitride element and the second group III nitride element of the group III nitride alloy based on the current position in the graded wurtzite group III nitride alloy layer from the second layer using the composition-polarization rate of change within the determined range of composition-polarization rate of change and the grading rate within the determined range of grading rate, forming a graded wurtzite group III nitride alloy layer on the second layer having a polarization doping concentration profile within the selected range of polarization doping concentration profile.

According to further embodiments, there is a method for forming a semiconductor device including a graded wurtzite group III nitride alloy layer on a second layer. The polarization doping concentration profile of the graded wurtzite group III nitride alloy layer is determined based on the product of the composition-polarization rate of change of the graded wurtzite group III nitride alloy layer and the grading rate of the graded wurtzite group III nitride alloy layer. The thickness of the graded wurtzite group III nitride alloy layer is also determined. The graded wurtzite group III nitride alloy layer includes a first group III nitride element and a second group III nitride element. Initial amounts of the first group III nitride element and the second group III nitride element used to form the graded wurtzite group III nitride alloy layer are then determined. The final amounts of the first group III nitride element and the second group III nitride element used to form the graded wurtzite group III nitride alloy layer are determined based on the polarization doping concentration profile, the thickness, and the initial amounts of the first group III nitride element and the second group III nitride element. Then, the initial amounts of the first group-III nitride element and the second group-III nitride element are adjusted based on the final amounts of the first group-III nitride element and the second group-III nitride element. Adjusted initial amounts of the first group III nitride element and the second group III nitride element are determined. The adjusted final amounts of the first group III nitride element and the second group III nitride element for forming the graded wurtzite group III nitride alloy layer are determined based on the polarization doping concentration profile, the thickness, and the adjusted initial amounts of the first group III nitride element and the second group III nitride element. The graded wurtzite group III nitride alloy layer is formed such that portions of the graded wurtzite group III nitride alloy layer adjacent to the second layer have adjusted initial amounts of the first group III nitride element and the second group III nitride element and portions of the graded wurtzite group III nitride alloy layer furthest from the second layer have adjusted final amounts of the first group III nitride element and the second group III nitride element.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

fig. 1 is a flow diagram of a method of forming a semiconductor device including a graded wurtzite group III nitride alloy layer on a second layer according to an embodiment;

fig. 2 is a schematic view of a semiconductor device including a graded wurtzite group III nitride alloy layer on a second layer, according to an embodiment;

FIG. 3 is a wurtzite group III nitride ternary alloy A according to an embodiment_xC_1-xA plot of the component-polarization rate of change κ (x) of N as a function of component;

fig. 4 is a flow diagram of a method of forming a semiconductor device including a graded wurtzite group III nitride alloy layer on a second layer according to an embodiment; and

fig. 5A and 5B are a flow chart of a method of forming a semiconductor device including a graded wurtzite group III nitride alloy layer on a second layer according to an embodiment.

Detailed Description

The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. For simplicity, the following examples are discussed with respect to the terminology and structure of wurtzite group III nitride ternary alloys and binary compositions.

Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Fig. 1 illustrates a method for forming a semiconductor device comprising a graded wurtzite group III nitride alloy layer on a second layer. First, a polarization doping concentration profile of the graded wurtzite group III nitride alloy layer is selected based on the intended function of the semiconductor device (step 105). Those skilled in the art will recognize that different types of semiconductor devices require different amounts of group III nitride alloy layer doping to operate as intended. Thus, one skilled in the art will understand how to select a polarization doping concentration profile to achieve the intended function of the layer. Next, the composition-polarization change rate of the graded wurtzite group III nitride alloy layer and the grading speed of the graded wurtzite group III nitride alloy layer are determined based on the polarization doping concentration distribution of the selected graded wurtzite group III nitride alloy layer (step 110). The composition-polarization change rate and the grading rate are both based on the composition of the first element and the second element of the wurtzite group III nitride alloy. Using the determined composition-polarization rate of change and the grading rate, the compositions of the first group III nitride element and the second group III nitride element of the wurtzite group III nitride alloy are adjusted based on the current position in the graded wurtzite group III nitride alloy layer from the second layer, forming a graded wurtzite group III nitride alloy layer having the selected polarization doping concentration profile on the second layer (step 115). The graded wurtzite group III nitride alloy layer can be formed using metal organic vapor deposition, molecular beam epitaxy, high temperature post deposition annealing, or any other related process.

Fig. 2 illustrates a semiconductor device formed according to the method of fig. 1. Specifically, semiconductor device 200 includes a graded wurtzite group III nitride alloy layer 210 formed on a second layer 205. As shown, the concentration (x) of the group III nitride element in the graded wurtzite group III nitride alloy layer 210 varies with the thickness (T) of the layer 210. Specifically, the portion of the graded wurtzite group III nitride alloy layer 210 adjacent to the second layer 205 hasAnd the portion of the graded wurtzite group III nitride alloy layer 210 furthest from the second layer 205 hasWhere a is a first group III nitride element of the wurtzite group III nitride alloy forming the layer 210, C is a second group III nitride element of the wurtzite group III nitride alloy forming the layer 210, and x is an amount of the corresponding group III nitride element in the wurtzite group III nitride alloy at a particular location within the thickness of the graded wurtzite group III nitride alloy layer 210. A and C are different group III nitride elements and x is a value of 0 to 1. Therefore, when x is 0, the portion of the graded wurtzite group III nitride alloy layer 210 adjacent to the second layer will not have the amount of the element a, and the graded layer can increase the amount of the element a with the formation of the thickness (T) of the layer. Of course, in other embodiments, x can be a non-zero value such that the closest second of the graded wurtzite group III nitride alloy layers 210Portions of the layer include some of the group III nitride elements a and C. The group III nitride elements a and C can be different elements among boron (B), aluminum (Al), indium (In), and gallium (Ga).

The second layer 205 can be a substrate, another graded wurtzite group III nitride alloy layer, another semiconductor layer, an insulating layer, or a metallic or conductive layer. Thus, the graded wurtzite group III nitride alloy layer 210 can be formed directly on the substrate or there can be one or more layers between the graded wurtzite group III nitride alloy layer 210 and the substrate.

Polarization doping concentration profile (σ)_P) Is the change in polarization (dP) relative to the change in position dl of a particular polarization within the layer, which is reflected in the following equation:

since the change in polarization is based on the composition (x) of the wurtzite group III nitride alloy at a specific position within the layer, equation (1) can be rewritten as:

the first term of equation (2) reflects the rate of change of polarization with respect to the alloy composition, which will be referred to as composition-to-polarization rate of change and can be represented by the following equation:

the second term of equation (2) reflects the grading rate (i.e., the rate at which the composition of x varies with the thickness of the layer) and can be represented by the following equation:

polarization doping concentration profile (σ)_P) Capable of grading the thickness of the wurtzite group III nitride alloy layer 210Either fixed or it can vary in the thickness of the graded wurtzite group III nitride alloy layer 210. When polarization doping concentration distribution (σ)_P) Component-rate of change of polarization (k) and fractionation velocity (v) while being fixed_g) Can be both fixed or both variable. Specifically, as the polarization (P) within the layer changes, the composition (x) of the wurtzite group III nitride alloy changes, and because of the composition-polarization rate of change (k) and the classification velocity (v)_g) Both based on component (x) and component variation, so both component-polarization rate of change and fractionation speed will remain fixed or vary. For example, when forming a metal contact on top of a graded wurtzite group III nitride alloy layer, a variable polarization doping concentration profile (σ) is desired_P) Since in this case it is generally desirable that the doping concentration on top of the graded wurtzite group III nitride layer is as high as possible to reduce the contact resistance. Thus, depending on the composition (x), the composition-polarization rate of change (k) and the grading velocity (v) at a specific location within the thickness of the layer_g) Either or both will be variable compared to other locations within the thickness of the layer. In other words, the determined grading rate will be fixed or variable over the thickness of the formed graded wurtzite group III nitride alloy layer, depending on the determined variable polarization doping concentration profile and the determined variable composition-to-polarization rate of change.

Because the composition-polarization rate of change is based on the polarization of a particular composition of the wurtzite group III nitride alloy, the polarization of the wurtzite group III nitride alloy for any particular amount x must be determined. Layer P (A) as reflected in equation (5) below_xC_1-xN) is a spontaneous polarization P for a specific value of x_SP(x) And piezoelectric polarization P of the same value for x_PZ(x) The sum of (a) and (b).

p(A_xC_1-xN)＝P_SP(x)+P_PZ(x) (5)

Substituting equation (5) into equation (3) enables the composition-polarization change rate to be expressed by the following equation:

piezoelectric polarization P_PZ(x) Based on the elastic constant and piezoelectric constant for a particular value of x, it can be expressed by the following equation:

wherein e₃₁(x) And e₃₃(x) Is the piezoelectric constant in C/m of a specific composition of wurtzite group III nitride alloy in the layer²，C₁₃(x) And C₃₃(x) Is the elastic constant in GPa of the particular component of the wurtzite group III nitride alloy in the layer, and a _ under _ strain (x) is the lattice constant in GPa of the particular component of the wurtzite group III nitride alloy in the layer when the component is strainedAnd a is_relax(x) Is the lattice constant in units of the particular component of the wurtzite group III nitride alloy in the layer when the component is fully relaxedSubstituting equation (7) into equation (6) can result in the following equation:

thus, for a particular component xo, the component-polarization rate of change can be represented by the following equation:

it can be understood from equation (9) that particular wurtzite group III nitride alloys at different compositions can have different rates of polarization change. In addition, certain wurtzite group III nitride alloys can have different rates of polarization change under different strain conditions. In addition, wurtzite group III nitride alloys of the same or different composition can have different rates of polarization change.

Referring again to FIG. 2, depending on the device application, the material composition x can be selected from the initial composition x according to a value of κ (x) within the range represented by equation (9)_initLinearly or non-linearly graded into a final component x_init。

The spontaneous polarization P of a plurality of wurtzite group III nitride alloys will now be described in more detail_SP(x) Piezoelectric constant e₃₁(x) And e₃₃(x) And elastic constant C₁₃(x) And C₃₃(x) And (4) determining.

The spontaneous polarization of wurtzite aluminum gallium nitride (AlGaN) layers, wurtzite indium gallium nitride (InGaN) layers, wurtzite indium aluminum nitride (InAlN) layers, and wurtzite boron aluminum nitride (BAlN) layers can be determined using the following equation:

piezoelectric constant e of wurtzite AlGaN layer, wurtzite InGaN layer, wurtzite InAlN layer, wurtzite BAIN layer and wurtzite BGaN layer₃₁And e₃₃Can be determined using the following equation:

e₃₁(Al_xGa_1-xN)＝-0.0573x²-0.2536x-0.3582 (15)

e₃₃(Al_xGa_1-xN)＝0.3949x²+0.6324x+0.6149 (16)

e₃₁(In_xGa_1-xN)＝0.2396x²-0.4483x-0.3399 (17)

e₃₃(In_xGa_1-xN)＝-0.1402x²＋0.5902x+0.6080 (18)

e₃₁(In_xAl_1-xN)＝-0.0959x²+0.239x-0.6699 (19)

e₃₃(In_xAl_1-xN)＝0.9329x²-1.5036x+1.6443 (20)

e₃₁(B_xAl_1-xN)＝1.7616x²-0.9003x-0.6016 (21)

e₃₃(B_xAl_1-xN)＝-4.0355x²+1.6836x+1.5471 (22)

e₃₁(B_xGa_1-xN)＝0.9809x²-0.4007x-0.3104 (23)

e₃₃(B_xGa_1-xN)＝-2.1887x²+0.8174x+0.5393 (24)

spring constant C₁₃And C₃₃The laws of Vegard can be used to determine and the binary constants can be determined using the following equations, or they can be obtained by directly calculating the ternary constants.

C₁₃(B_xAl_1-xN)＝xC₁₃(BN)+(1-x)C₁₃(AlN) (25)

C₁₃(B_xGa_1-xN)＝xC₁₃(BN)+(1-x)C₁₃(GaN) (26)

C₁₃(Al_xGa_1-xN)＝xC₁₃(AlN)+(1-x)C₁₃(GaN) (27)

C₁₃(In_xGa_1-xN)＝xC₁₃(InN)+(1-x)C₁₃(GaN) (28)

C₁₃(In_xAl_1-xN)＝xC₁₃(InN)+(1x)C₁₃(AlN) (29)

C₃₃(B_xAl_1-xN)＝xC₃₃(BN)+(1-x)C₃₃(AlN)(30)

C₃₃(B_xGa_1-xN)＝xC₃₃(BN)+(1-x)C₃₃(GaN) (31)

C₃₃(Al_xGa_1-xN)＝xC₃₃(AlN)+(1-x)C₃₃(GaN) (32)

C₃₃(In_xGa_1-xN)＝xC₃₃(InN)+(1-x)C₃₃(GaN) (33)

C₃₃(In_xAl_1-xN)＝xC₃₃(InN)+(1-x)C₃₃(AlN) (34)

The lattice constants of wurtzite BAIN, wurtzite BGaN, wurtzite InAlN, wurtzite AlGaN and wurtzite InGaN can be calculated as follows:

FIG. 3 is wurtzite group III nitride ternary alloy A_xC_1-xComposition-polarization change rate κ (x)) of N as a function of composition x. As can be seen from the graph, the component-polarization change rate κ (x)) is different for different components x. The component-polarization change rate can be negative or positive for inducing free electrons or holes, respectively. Therefore, the selection of the correct range of grading components is very important for efficient polarization doping. The yeast is prepared from yeastThe line graph can be used in conjunction with or in place of the above equation to select wurtzite group III nitride ternary alloy a_xC_1-xN to obtain a specific composition-polarization change rate κ (x). Similarly, the graph can be used in conjunction with or in place of the above equation to select a particular composition-polarization change rate κ (x) to achieve wurtzite group III nitride ternary alloy a_xC_1-xN, a specific component x.

The method of fig. 1 provides specific composition-polarization rates of change and grading rates to achieve a selected polarization doping concentration profile. However, due to limitations in the techniques used to form graded wurtzite group III nitride alloy layers, specific composition-polarization rates and grading rates may not be achievable. In practice, sometimes no specific value of the polarization doping concentration profile is required. Instead, a range of values can also be used in some cases, while still achieving the desired effect. A method for employing a range of polarization doping concentration profiles according to an embodiment will now be described with reference to fig. 4, which is a flow chart of a method for forming a semiconductor device including a graded wurtzite group III nitride alloy layer on a second layer according to an embodiment.

First, a range of polarization doping concentration profiles for the graded wurtzite group III nitride alloy layer is selected based on the intended function of the semiconductor device (step 405). Next, based on the selected polarization doping concentration distribution range, a range of composition-polarization change rates of the graded wurtzite group III nitride alloy layer and a range of grading speeds of the graded wurtzite group III nitride alloy layer are determined (step 410). The range of composition-polarization change rates and the range of classification rates are based on the composition of the first element and the second element of the wurtzite group III nitride alloy. Next, using the composition-polarization change rate within the determined range of composition-polarization change rates and the grading speed within the determined range of grading speeds, the compositions of the first group III nitride element and the second group III nitride element of the wurtzite group III nitride alloy are adjusted based on the current position in the graded wurtzite group III nitride alloy layer from the second layer, forming a graded wurtzite group III nitride alloy layer having a polarization doping concentration distribution within the selected polarization doping concentration distribution range on the second layer (step 415).

Due to the relationship between the component-polarization change rate and the classification speed, as reflected in equation (2), any component-polarization change rate and classification speed cannot be arbitrarily selected from the range. Instead, each component-polarization rate of change in this range is associated with a staging speed in its own range.

The method of fig. 4 provides additional flexibility as compared to the method of fig. 1, in that the range of polarization doping concentration profiles provides a range of composition-polarization rates of change and grading rates from which selection can be made based on the particular technique used to form the graded wurtzite group III nitride alloy layer.

A large range of graded compositions may result in a graded wurtzite group III nitride alloy layer having a large lattice mismatch with the second layer, which may result in reduced performance of semiconductor devices having graded wurtzite group III nitride alloy layers. This may be due to the initial value of x being chosen too large resulting in a large fractionation component. Fig. 5A and 5B illustrate a method of solving this problem by adjusting the initial value of x.

First, a polarization doping concentration profile of the graded wurtzite group III nitride alloy layer is determined based on a product of a composition-polarization change rate of the graded wurtzite group III nitride alloy layer and a grading rate of the graded wurtzite group III nitride alloy layer (step 505). Next, the thickness of the graded wurtzite group III nitride alloy layer is determined (step 510). The graded wurtzite group III nitride alloy layer includes a first group III nitride element and a second group III nitride element.

Initial amounts of the first group III nitride element and the second group III nitride element used to form the graded wurtzite group III nitride alloy layer are then determined (step 515). Final amounts of the first group III nitride element and the second group III nitride element for forming the graded wurtzite group III nitride alloy layer are determined based on the polarization doping concentration profile, the thickness, and the initial amounts of the first group III nitride element and the second group III nitride element (step 520). If the final amounts of the first group III-nitride element and the second group III-nitride element are acceptable ("YES" path of decision step 525), the graded wurtzite group III-nitride alloy layer is formed using the initial amounts and the final amounts of the first group III-nitride element and the second group III-nitride element (step 530).

If the final amounts of the first group III-nitride element and the second group III-nitride element are not acceptable ("NO" path out of decision step 525), the initial amounts of the first group III-nitride element and the second group III-nitride element are adjusted (step 535). Adjusted final amounts of the first group III nitride element and the second group III nitride element for forming the graded wurtzite group III nitride alloy layer are determined based on the polarization doping concentration profile, the thickness, and the adjusted initial amounts of the first group III nitride element and the second group III nitride element (step 540). The graded wurtzite group III nitride alloy layer is formed such that portions of the graded wurtzite group III nitride alloy layer adjacent to the second layer have adjusted initial amounts of the first group III nitride element and the second group III nitride element and portions of the graded wurtzite group III nitride alloy layer furthest from the second layer have adjusted final amounts of the first group III nitride element and the second group III nitride element (step 545).

Although the discussion above refers to wurtzite group III nitride alloys, the discussion applies equally to wurtzite group III nitride binary compositions (e.g., AlN, GaN, etc.). Thus, any of the methods discussed above can be employed using the wurtzite group III nitride binary composition. Thus, reference to a wurtzite group III nitride composition or wurtzite group III nitride layer comprises such a composition or layer as an alloy or as a binary composition.

The discussion above relates to wurtzite ternary group III nitride alloys. One skilled in the art will recognize that wurtzite ternary group III nitride alloys may contain minor concentrations of additional elements. Trace concentrations of these additional elements occur due to contaminants or impurities that become part of the layer during the process of forming the graded wurtzite group III nitride alloy layer. These contaminants or impurities are usually less than0.1% of the total composition of the hierarchical wurtzite group III nitride ternary alloy layer. Furthermore, when an insignificant amount of other elements comprising other group III elements is present in addition to the two group III elements, the skilled person will also consider the hierarchical wurtzite group III nitride alloy as a ternary alloy. One skilled in the art would consider the element to be an insignificant amount at a concentration of 0.1% or less. Thus, for example, those skilled in the art will recognize that Al is included_xGa_1-x-yIn_yThe layer of N is a ternary alloy, where y ≦ 0.1% because it contains an insignificant amount of indium. Similarly, wurtzite group III nitride binary compositions can contain insignificant concentrations of additional elements while still being considered binary compositions.

The disclosed embodiments provide methods for forming graded wurtzite group III nitride alloy layers in semiconductor devices. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a thorough understanding of the claimed invention. However, it will be understood by those skilled in the art that various embodiments may be practiced without these specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed, including any devices or systems that make and use the subject matter and methods of performing any combination, to enable any person skilled in the art to practice the subject matter. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

Reference to the literature

[1] "Polarization-Induced Hole while Wide-Band-Gap UniaxialSemiconductor hybrids", Simon et al, SCIENCE, year 2010, month 01: 60-64.