阅读说明：本技术 外延片及光电探测器芯片 (Epitaxial wafer and photoelectric detector chip ) 是由 孙博 赵泽平 焦晓飞 韩雪妍 刘建国 于 2021-08-27 设计创作，主要内容包括：本发明提供了一种外延片,包括：衬底(2)及依次层叠在所述衬底(2)表面的N型欧姆接触层(3)、收集层(5)、崖层(6)、过渡层、本征吸收层(9)、P型吸收层(10)、阻挡层(11)、P型欧姆接触层(12)；所述P型吸收层(10)在本征吸收层(9)指向阻挡层(11)的方向上掺杂浓度逐渐增大。本发明通过将吸收层设计为本征吸收层和P型渐变吸收层,在不降低响应度的前提下,提高了探测器的带宽和饱和特性；通过添加崖层,提高了吸收层的电场强度,提高了电子漂移速度,提高了探测器带宽和饱和特性；通过在InP材料和InGaAs材料之间添加InGaAsP过渡层,减小了电子在异质结交界处的堆积,提高了探测器带宽和饱和特性。(The invention provides an epitaxial wafer, comprising: the device comprises a substrate (2), and an N-type ohmic contact layer (3), a collection layer (5), a cliff layer (6), a transition layer, an intrinsic absorption layer (9), a P-type absorption layer (10), a barrier layer (11) and a P-type ohmic contact layer (12) which are sequentially stacked on the surface of the substrate (2); the doping concentration of the P-type absorption layer (10) is gradually increased in the direction of the intrinsic absorption layer (9) pointing to the barrier layer (11). According to the invention, the absorption layer is designed into the intrinsic absorption layer and the P-type gradual change absorption layer, so that the bandwidth and saturation characteristics of the detector are improved on the premise of not reducing the responsivity; by adding the cliff layer, the electric field intensity of the absorption layer is improved, the electron drift speed is improved, and the bandwidth and the saturation characteristic of the detector are improved; by adding the InGaAsP transition layer between the InP material and the InGaAs material, the accumulation of electrons at the junction of the heterojunction is reduced, and the bandwidth and the saturation characteristic of the detector are improved.)

1. An epitaxial wafer, comprising:

the device comprises a substrate (2), and an N-type ohmic contact layer (3), a collection layer (5), a cliff layer (6), a transition layer, an intrinsic absorption layer (9), a P-type absorption layer (10), a barrier layer (11) and a P-type ohmic contact layer (12) which are sequentially stacked on the surface of the substrate (2);

the doping concentration of the P-type absorption layer (10) is gradually increased in the direction of the intrinsic absorption layer (9) pointing to the barrier layer (11).

2. Epitaxial wafer according to claim 1, characterized in that the intrinsic absorption layer (9) is InGaAs and the intrinsic absorption layer (9) is doped with a low concentration, not more than 2.0 x 10¹⁶cm^-3。

3. Epitaxial wafer according to claim 1, characterized in that the material of the P-type absorption layer (10) is InGaAs, and the doping concentration of the P-type absorption layer (10) is not less than 1.0 x 10¹⁷cm^-3And is not higher than 1.0X 10¹⁹cm^-3。

4. Epitaxial wafer according to claim 1, characterized in that the ratio of the widths of the intrinsic absorber layer (9) and the P-type absorber layer (10) is a preset ratio at which the maximum broadband is obtained.

5. The epitaxial wafer according to claim 1, characterized in that the transition layers comprise a first transition layer (7) and a second transition layer (8), the first transition layer (7) being InGaAsP with a forbidden bandwidth of 1.1 μm, the second transition layer (8) being InGaAsP with a forbidden bandwidth of 1.4 μm, wherein the second transition layer (8) is close to the intrinsic absorption layer (9).

6. The epitaxial wafer of claim 1, wherein the transition layer is doped with a low concentration of no more than 2.0 x 10¹⁶cm^-3。

7. Epitaxial wafer according to claim 1, characterized in that the material of the cliff layer (6) is InP, dopedThe concentration is more than 1.0 × 10¹⁷cm^-3Less than 1.0X 10¹⁸cm^-3。

8. Epitaxial wafer according to claim 1, characterized in that the material of the collector layer (5) and the barrier layer (11) is InP, the collector layer (5) is doped N-type and the barrier layer (11) is doped P-type.

9. The epitaxial wafer according to claim 1, characterized in that the material of the N-type ohmic contact layer (3) is InP doped in a manner of N-type doping with a doping concentration of not less than 1.0 x 10¹⁹cm^-3(ii) a The P-type ohmic contact layer (12) is made of InGaAs, the doping mode is P-type doping, and the doping concentration is not less than 1.0 multiplied by 10¹⁹cm^-3。

10. A photodetector chip using the epitaxial wafer according to any one of claims 1 to 9, wherein the photodetector chip comprises:

an epitaxial wafer;

the anti-reflection film (1) is formed on the opposite surface of the substrate (2) of the epitaxial wafer;

an N electrode (4) formed on the N-type ohmic contact layer (3) of the epitaxial wafer;

and the P electrode (14) is formed on the P type ohmic contact layer (12) of the epitaxial wafer.

Technical Field

The invention relates to the field of semiconductor devices, in particular to an epitaxial wafer and a photoelectric detector chip.

Background

With the continuous acceleration of the informatization process of the modern society, the communication capacity is increased in an explosive manner, the photoelectric detector is used as a core device in a link of an optical transmission system and is used for realizing the photoelectric conversion of signals, and the performance of the photoelectric detector directly determines the performance of the communication system. The large-capacity ultrahigh-speed optical communication system puts requirements on wide bandwidth, high responsivity and high saturation input on the photoelectric detector.

In a traditional single-row carrier detector (UTC-PD), an absorption layer is doped in a P type mode, the doping concentration is high, an electric field in the layer is extremely low, electrons mainly take low-speed diffusion motion as a main mode, and the reduction of the thickness of the absorption layer can cause the reduction of the responsivity, so that the high bandwidth and the high responsivity are difficult to achieve at the same time.

Disclosure of Invention

Technical problem to be solved

In view of this, the invention provides a new structure of an epitaxial wafer in a photodetector chip for the actual requirements of broadband high saturation input and high efficiency, and inserts an intrinsic absorption layer below a P-type absorption layer, thereby improving the electric field in the absorption layer, improving the electron drift velocity, and improving the bandwidth and saturation characteristics of the device while maintaining high responsivity.

(II) technical scheme

One aspect of the present invention provides an epitaxial wafer, including: the semiconductor device comprises a substrate 2, and an N-type ohmic contact layer 3, a collection layer 5, a cliff layer 6, a transition layer, an intrinsic absorption layer 9, a P-type absorption layer 10, a barrier layer 11 and a P-type ohmic contact layer 12 which are sequentially stacked on the surface of the substrate 2; the P-type absorption layer 10 has a doping concentration that gradually increases in a direction in which the intrinsic absorption layer 9 points toward the barrier layer 11.

Optionally, the intrinsic absorption layer 9 is InGaAs, and the intrinsic absorption layer 9 is doped at a low concentration, where the doping concentration is not greater than 2.0 × 10¹⁶cm^-3。

Optionally, the material of the P-type absorption layer 10 is InGaAs, and the doping concentration of the P-type absorption layer 10 is not less than 1.0 × 10¹⁷cm^-3And is not higher than 1.0X 10¹⁹cm^-3。

Alternatively, the width ratio of the intrinsic absorption layer 9 and the P-type absorption layer 10 is a preset ratio at which a maximum broadband can be obtained.

Optionally, the transition layers include a first transition layer 7 and a second transition layer 8, the first transition layer (7) is InGaAsP with a forbidden bandwidth of 1.1 μm, the second transition layer (8) is InGaAsP with a forbidden bandwidth of 1.4 μm, and the second transition layer 8 is close to the intrinsic absorption layer 9.

Optionally, the transition layer is doped at a low concentration, wherein the doping concentration is not more than 2.0 × 10¹⁶cm^-3。

Optionally, the material of the cliff layer 6 is InP with a doping concentration greater than 1.0 × 10¹⁷cm^-3Less than 1.0X 10¹⁸cm^-3。

Optionally, the collection layer 5 and the barrier layer 11 are made of InP, the doping manner of the collection layer 5 is N-type doping, and the doping manner of the barrier layer 11 is P-type doping.

Optionally, the N-type ohmic contact layer 3 is made of InP and doped in an N-type manner, and the doping concentration is not less than 1.0 × 10¹⁹cm^-3(ii) a The P-type ohmic contact layer 12 is made of InGaAs, the doping mode is P-type doping, and the doping concentration is not less than 1.0 multiplied by 10¹⁹cm^-3。

In another aspect, the present invention provides a photodetector chip using the above epitaxial wafer, where the photodetector chip includes: an epitaxial wafer; an antireflection film 1 formed on the opposite surface of the substrate 2 of the epitaxial wafer; the N electrode 4 is formed on the N-type ohmic contact layer 3 of the epitaxial wafer; and the P electrode 14 is formed on the P-type ohmic contact layer 12 of the epitaxial wafer.

(III) advantageous effects

The invention has the following beneficial effects:

(1) by designing the absorption layer into the intrinsic absorption layer and the P-type gradient absorption layer, the bandwidth and saturation characteristics of the detector are improved on the premise of not reducing the responsivity.

(2) By adding the cliff layer, the electric field intensity of the absorption layer is improved, the electron drift speed is improved, and the bandwidth and the saturation characteristic of the detector are improved.

(3) By adding the InGaAsP transition layer between the InP material and the InGaAs material, the accumulation of electrons at the junction of the heterojunction is reduced, and the bandwidth and the saturation characteristic of the detector are improved.

(4) By polishing and thinning the back of the InP substrate and coating an antireflection film, the optical coupling efficiency is improved, and the responsivity of the detector is improved.

Drawings

Fig. 1 schematically shows a structural diagram of an epitaxial wafer and a photodetector chip provided by the present invention.

Fig. 2 schematically shows a process flow diagram of an epitaxial wafer and a photodetector chip provided by the present invention.

[ description of reference ]

1-an antireflection film;

2-a substrate;

a 3-N type ohmic contact layer;

4-N electrode;

5-a collector layer;

6-cliff layer;

7-a first transition layer;

8-a second transition layer;

9-intrinsic absorber layer;

a 10-P type absorption layer;

11-a barrier layer;

12-P type ohmic contact layer;

13-a passivation layer;

14-P electrode.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.

The invention provides an epitaxial wafer, and referring to fig. 1, fig. 1 shows a structure of the epitaxial wafer provided by the invention, which comprises: the semiconductor device comprises a substrate 2, and an N-type ohmic contact layer 3, a collection layer 5, a cliff layer 6, a transition layer, an intrinsic absorption layer 9, a P-type absorption layer 10, a barrier layer 11 and a P-type ohmic contact layer 12 which are sequentially stacked on the surface of the substrate 2. Wherein, the doping concentration of the P-type absorption layer 10 is gradually increased in the direction of the intrinsic absorption layer 9 pointing to the barrier layer 11.

In an embodiment of the present invention, the thickness of the substrate 2 is not less than 200 μm, and InP material is used, so as to increase the conductivity, the substrate 2 can be doped with N-type with low concentration, the doping concentration is 1.0 × 10¹⁶cm^-3。

The intrinsic absorption layer 9 and the P-type absorption layer 10 are both InGaAs, and the total thickness of the intrinsic absorption layer 9 and the P-type absorption layer 10 is 200-1000 nm. The intrinsic absorption layer 9 is doped at a low concentration to increase its conductivity, the doping concentration being not more than 2.0X 10¹⁶cm^-3The doping concentration is low and can still be approximately regarded as an intrinsic absorption layer. The doping mode of the P-type absorption layer 10 is P-type gradual doping, the doping concentration is gradually increased from the intrinsic absorption layer 9 to the barrier layer 11, and the doping concentration is not less than 1.0 multiplied by 10¹⁷cm^-3And is not higher than 1.0X 10¹⁹ cm^-3. In the P-type absorption layer, effective carriers are electrons, the electrons perform diffusion motion in the P-type absorption layer, and in the intrinsic absorption layer, the effective carriers are electrons and holes and perform drift motion under the action of an electric field. The gradual doping can generate a built-in electric field in the P-type absorption layer, and the bandwidth and the saturation characteristic are improved.

The width ratio of the intrinsic absorption layer 9 and the P-type absorption layer 10 is a preset ratio, and a maximum broadband can be obtained at the preset ratio. I.e. in case the absorption layer is fixed, i.e. the responsivity is fixed, the maximum bandwidth can be obtained by adjusting the ratio of the intrinsic absorption layer 9 and the P-type absorption layer 10.

The transition layer is two-layer, and the one deck transition layer that is close to cliff layer is first transition layer 7, and the material is InGaAsP, Q1.1, and the one deck transition layer that is close to intrinsic absorption layer is second transition layer 8, and the material is InGaAsP, Q1.4, and every layer thickness is 10 ~ 20 nm. The transition layer is doped at low concentration, with the doping concentration not greater than 2.0 × 10¹⁶cm^-3. By adding an InGaAsP transition layer between the InP material and the InGaAs material, the electron concentration at the heterojunction interface is reducedAnd accumulation improves the bandwidth and saturation characteristics of the detector. Wherein InGaAsP Q1.1 and InGaAsP Q1.4 represent different compositions of InGaAsP, and Q1.4 and Q1.1 respectively represent forbidden band widths of 1.4 μm and 1.1 μm. The components of the four elements of InGaAsP can be calculated according to the forbidden bandwidth.

The cliff layer 6 is made of InP with the thickness of 30-60 nm and the doping concentration of more than 1.0 multiplied by 10¹⁷cm^-3Less than 1.0X 10¹⁸cm^-3. The ionization donor after the cliff layer 6 is exhausted generates space positive charge, so that the electric field intensity of the transition layer and the absorption layer is increased, the accumulation of electrons in the depletion region is reduced, and the bandwidth and the saturation characteristic of the detector are improved.

The collection layer 5 and the barrier layer 11 are made of InP, the collection layer 5 is doped in an N-type manner, and the barrier layer 11 is doped in a P-type manner. The N-type ohmic contact layer 3 is made of InP and doped in N-type manner with a doping concentration of not less than 1.0 × 10¹⁹ cm^-3(ii) a The P-type ohmic contact layer 12 is made of InGaAs, the doping mode is P-type doping, and the doping concentration is not less than 1.0 × 10¹⁹cm^-3。

The invention also provides a photoelectric detector chip applying the epitaxial wafer, and referring to fig. 1, the photoelectric detector chip comprises: an epitaxial wafer; an antireflection film 1 formed on the opposite surface of the substrate 2 of the epitaxial wafer; the N electrode 4 is formed on the N-type ohmic contact layer 3 of the epitaxial wafer; and the P electrode 14 is formed on the P-type ohmic contact layer 12 of the epitaxial wafer. In an embodiment of the present invention, a manufacturing process of a photodetector chip is as follows:

growing an epitaxial wafer on the substrate 2;

etching from the direction of the P-pole ohmic contact layer 12 to the substrate 2 to the N-pole ohmic contact layer 3 to form a P-stage mesa as shown in FIG. 1;

etching from the direction of the N-pole ohmic contact layer 3 to the substrate 2 to form N mesas as shown in FIG. 1;

a silicon dioxide passivation layer 13 grows on the N-pole ohmic contact layer 3, the P-pole ohmic contact layer 12 and the side wall of the P platform;

opening an electrode window on the passivation layer 13, and manufacturing a P electrode 14 and an N electrode 4;

carrying out annealing alloy treatment on the P electrode 14 and the N electrode 4;

and polishing the back surface of the substrate 2 to thin and grow an antireflection film 1.

According to the invention, the back surface of the substrate 2 is polished and thinned and the antireflection film 2 is coated, so that the optical coupling efficiency is improved, and the responsivity of the detector is improved.

In an embodiment of the present invention, the structure of the epitaxial wafer is:

firstly, an N-electrode ohmic contact layer 3 is grown on an InP substrate 2, the material is InP, the thickness is 100nm, the doping type is N-type doping, the impurity is silicon, the doping concentration is 1.0 multiplied by 10¹⁹cm^-3。

A collecting layer 5 is grown, the material is InP, the thickness is 400nm, the doping type is N-type doping, the impurity is silicon, and the doping concentration is 1.0 multiplied by 10¹⁶cm^-3。

Growing a cliff layer 6, which is made of InP and has a thickness of 50nm, is doped with N-type impurity, silicon and a doping concentration of 4.0 × 10¹⁷cm^-3。

Growing two transition layers, one layer near the cliff layer is made of InGaAsP and Q1.1, the other layer is made of InGaAsP and Q1.4, the thicknesses of the two layers are both 15nm, the doping type is N-type doping, the impurity is silicon, and the doping concentration is 1.0 multiplied by 10¹⁶cm^-3。

Growing an intrinsic absorption layer 9 of InGaAs with a thickness of 200nm, N-type doping, silicon as impurity and a doping concentration of 1.0 × 10¹⁶cm^-3。

A P-type absorption layer 10 is grown. The material is InGaAs with a thickness of 400nm, the doping type is P-type doping, the impurity is Zn, and the doping concentration is 5.0 × 10¹⁷cm^-3～2.0×10¹⁸cm^-3The doping concentration increases gradually from the intrinsic absorber layer 9 towards the barrier layer 11.

Growing a barrier layer 11 made of InP with a thickness of 100nm, doping with P-type dopant, zinc as impurity and a doping concentration of 1.5 × 10¹⁸cm^-3。

Growing a P-type ohmic contact layer 12 of the materialInGaAs with a thickness of 50nm, a P-type doping type, Zn as impurity, and a doping concentration of 2.0 × 10¹⁹cm^-3。

Alternatively, the above structure can be fabricated by using an MOCVD method.

In another embodiment of the present invention, as shown in fig. 2, the process flow of the photodetector chip is as follows:

1. cleaning epitaxial wafer and mask

The method comprises heating trichloroethylene in water bath for 10min, heating with acetone in water bath for 5min (2 groups), heating with ethanol in water bath for 5min (2 groups), repeatedly washing with deionized water until organic matter is removed, and blowing with nitrogen gas. If the surfaces of the epitaxial wafer and the mask have organic matters which are difficult to remove, an oxygen plasma photoresist removing method can be adopted.

2. Growing SiO₂Mask film

SiO deposition by PECVD method₂And the thickness is 600 nm.

3. Photoetching to form P-stage shape

And forming glue masking on the P electrode table top, wherein glue is arranged on the P electrode table top, no glue is arranged in the rest areas, and the glue thickness is 2 um.

ICP etching P bench

Firstly, transferring the pattern to SiO by HF wet etching₂And etching the layer by using silicon dioxide as a mask by adopting an ICP (inductively coupled plasma) method until the N-pole ohmic contact layer 3 is formed.

5. Growing SiO₂Mask film

SiO deposition by PECVD (plasma enhanced chemical vapor deposition)₂And the thickness is 600 nm.

6. Photoetching to form N-stage shape

And forming glue masking on the N electrode table top, wherein glue is arranged on the N electrode table top, no glue is arranged in the rest areas, and the glue thickness is 2 um.

ICP etching N platform

Pattern transfer to SiO using HF wet etch₂The layer is etched by an ICP (inductively coupled plasma) method using silicon dioxide as a mask until the substrate 2 is etched.

HF SiO removal₂

With HF + NH₄F+H₂Removing SiO by O (3: 6: 10) proportioning liquid₂Putting the slices into a polytetrafluoroethylene flower basket, putting proportioning liquid for corrosion for 20-30s, and observing whether the surface color is completely processed. And (4) cleaning according to the step 1 after the corrosion is finished.

9. Growing SiO₂Passivation layer

Respectively cleaning the surface of a sample by using trichloroethylene, acetone and ethanol according to the step 1, removing a damage layer caused by dry etching by using a freezing point grating bromine solution after drying by using nitrogen, soaking for 20min by using ammonium sulfide with the concentration of more than 8%, washing by using deionized water, drying by using nitrogen, cleaning according to the step 1 to remove residual ammonium sulfide passivation solution, immediately growing a layer of SiO (silicon dioxide) passivation solution by using PECVD (plasma enhanced chemical vapor deposition), and blow-drying₂And the thickness is 350 nm.

10. Making electrode windows

The contact electrodes include a P electrode 14 and an N electrode 4. Firstly, positive glue is adopted to photoetch the electrode window pattern, so that no glue is arranged at the electrode window, and glue is arranged in other areas. By HF + NH₄F+H₂And removing the passivation layer at the electrode window by using O (3: 6: 10) corrosive liquid to expose the ohmic contact surface of the electrode.

11. Making metal electrodes

And after the last step, the photoresist is reserved, an electrode metal Ti/Au alloy is grown in a magnetron sputtering mode, and the metal electrode is prepared by soaking and stripping acetone.

12. Annealed alloy

Rapid annealing of the alloy is required to provide good ohmic contact between the semiconductor and the metal, increasing adhesion. The temperature was 390 ℃ for 40 s.

13. Polishing and thinning the back

And thinning the back surface of the device to 200 mu m, and then polishing by using grinding fluid. After the steps are finished, the polished surface of the sample is very smooth, and the surface relief of the polished surface measured by a step profiler is less than 5 microns, so that the expected requirement is met.

14. Back growth antireflection film 1

Adopting PECVD equipment to grow the material with the refractive index of 2200nm thick SiN_xThe film is used to reduce the reflectance of the polished surface, which is expected to be less than 1%. By SiH₄And NH₃As a reaction gas. The deposition conditions were: the substrate temperature was 250 ℃, the pressure in the reaction chamber was 102Pa, and the rf power was 15W.

15. Back preparation positioning window

Plasma dry etching is used to remove excess SiN_xA circular ring is formed to indicate the incident position of the backlight.

The epitaxial wafer and the photoelectric detector chip provided by the invention have the following beneficial effects:

(1) by designing the absorption layer into the intrinsic absorption layer and the P-type gradient absorption layer, the bandwidth and saturation characteristics of the detector are improved on the premise of not reducing the responsivity.

(2) By adding the cliff layer, the electric field intensity of the absorption layer is improved, the electron drift speed is improved, and the bandwidth and the saturation characteristic of the detector are improved.

(3) By adding the InGaAsP transition layer between the InP material and the InGaAs material, the accumulation of electrons at the junction of the heterojunction is reduced, and the bandwidth and the saturation characteristic of the detector are improved. Meanwhile, the InP material and the InGaAs material also have the following advantages: in the photoelectric effect, InGaAs can respond well to light of 1550nm wavelength, 1550nm is a communication wavelength, and InP and InGaAs are lattice-matched to a high degree.

(4) By polishing and thinning the back of the InP substrate and coating an antireflection film, the optical coupling efficiency is improved, and the responsivity of the detector is improved.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.