阅读说明：本技术 高效率氧化型垂直共振腔面发射激光器及其制造方法 (High-efficiency oxidized vertical resonant cavity surface emitting laser and manufacturing method thereof ) 是由 李亨株 于 2019-07-05 设计创作，主要内容包括：本发明涉及一种垂直共振腔面发射激光器(VCSEL)及其制造方法,更详细而言,涉及一种发射峰值波长为860nm的激光的高效率氧化型垂直共振腔面发射激光器及其制造方法。本发明的氧化型垂直共振腔面发射激光器的特征在于,上部电极和上部分布式布拉格反射器之间具有导电性电流扩散层,所述导电性电流扩散层使具有860±10nm的峰值波长的激光透射。(The present invention relates to a Vertical Cavity Surface Emitting Laser (VCSEL) and a method of manufacturing the VCSEL, and more particularly, to a high-efficiency oxidized VCSEL that emits laser light having a peak wavelength of 860nm and a method of manufacturing the VCSEL. The oxidized vertical cavity surface emitting laser according to the present invention is characterized in that a conductive current diffusion layer that transmits laser light having a peak wavelength of 860 ± 10nm is provided between the upper electrode and the upper distributed bragg reflector.)

1. An oxidized vertical cavity surface emitting laser characterized by having a conductive current diffusion layer between an upper electrode and an upper distributed Bragg reflector, the conductive current diffusion layer transmitting laser light having a peak wavelength of 860 + -10 nm.

2. An oxidized vertical cavity surface emitting laser according to claim 1 wherein said conductive current spreading layer is a non-oxidizing barrier layer.

3. An oxidized vertical cavity surface emitting laser according to claim 2 wherein said non-oxidizing barrier layer is an aluminum-free layer.

4. An oxidized vertical cavity surface emitting laser according to claim 1, wherein said current diffusion layer is a GaP layer.

5. An oxidized VCSEL according to claim 1 wherein the GaP layer contains a metal and/or a non-metal dopant.

6. The oxidized vertical cavity surface emitting laser according to claim 5, wherein said dopant is one or more selected from the group consisting of magnesium, zinc and carbon.

7. An oxidized vertical cavity surface emitting laser according to claim 5, wherein said GaP layer has a thickness of 1 μm or more.

8. The oxidized VCSEL of claim 1, comprising a lower electrode, a substrate, a lower DBR, an active layer, an upper DBR, an upper electrode, and an oxide layer.

9. An oxidized vertical cavity surface emitting laser according to claim 8 wherein said active layer is comprised of GaAs quantum wells and AlGaAs quantum barrier layers.

10. An oxidized vertical cavity surface emitting laser according to claim 8, wherein the thickness of said GaP layer is 3 μm.

11. An oxidized vertical cavity surface emitting laser according to claim 8 wherein said oxide layer is located between layers of the upper p-DBR.

12. The oxidized VCSEL of claim 8, wherein the oxidized VCSEL operates at 10 to 40mA current.

13. An oxidized vertical cavity surface emitting laser according to claim 8 wherein said upper electrode is a transparent electrode selected from Indium Tin Oxide (ITO), ZnO or AZO.

14. The oxidized VCSEL of claim 8, further comprising an anti-reflection layer on the current spreading layer of the oxidized VCSEL.

Technical Field

The present invention relates to a Vertical Cavity Surface Emitting Laser (VCSEL) and a method of manufacturing the VCSEL, and more particularly, to a high-efficiency oxidized VCSEL that emits laser light having a peak wavelength of 860nm and a method of manufacturing the VCSEL.

Background

A general Vertical Cavity Surface Emitting Laser (VCSEL) has a low efficiency as compared with a conventional edge Emitting Laser parallel to a substrate, but can be used in the field of a conventional light Emitting diode since it emits Laser light in a direction perpendicular to the substrate, and thus has a high marketability.

As shown in fig. 1, this vertical cavity surface emitting laser 10 has a lower electrode 1, a substrate 2, a lower Distributed Bragg Reflector (DBR) 3, an active layer 4, a current window (current window)5 for emitting resonant laser light, an oxide layer 6 formed in a manner to surround the current window, an upper Distributed Bragg Reflector 7 formed on the upper surfaces of both the current window 5 and the oxide layer 6, and a columnar structure in which an upper electrode 8 is laminated. A trench (trench)9 is formed around the laser beam, and the laser beam is emitted from the upper portion.

Typically, the trench 9 is a circular trench and is formed by a dry etching (dry etching) technique. The oxide layer 6 is formed by oxidizing the peripheral portion of the current window 5 by the oxidizing agent injected through the trench 9, and the remaining central portion which is not oxidized forms the current window 5, and the diameter of the current window is adjusted by adjusting the oxidation time. Also, the upper and lower DBRs are applied to the upper and lower portions of the active layer through an epitaxial (epitaxial) process. In VCSELs emitting light of 800 to 1000nm, Al is generally used_xGa_1-xAs/Al_yGa_1-yAs(0.8<x<1，0<y<0.2) DBR of a laminated structure.

Therefore, in the manufacturing process, a current window (oxide aperture), an upper DBR and a lower DBR are necessary for resonance laser characteristics, but there is a problem in that since the materials used in these two are the same material, the uppermost portion of the upper p-DBR is oxidized (oxidation) together with the current window in the oxidation process for forming the current window, and thus a probability of generation of defects is high. The oxidation process is to implant H₂O vapor and using Al as a current window by high-temperature water vapor_0.98Ga_0.02Al of As layer reacts to produce Al_xO_yProcedure of layer, but from Al_xGa_1-xAs/Al_yGa_1-yThe upper and lower DBRs of As contain Al, and thus a portion of them are oxidized together.

Fig. 2 (a) shows an SEM image of a DBR damage form occurring during oxidation, and when p-metal (p-metal) is applied to a DBR damaged sample, phenomena such as electrode peeling (peeling) and uneven current injection (efficiency reduction) occur thereafter. Fig. 2 (b) shows the shape of the current window, the black stripe shape being a trench (recess) region, the middle region being a column region emitting light, and the brighter portion being an oxidized portion. The central dark circular portion is the light emitting area where light is directly emitted, which can also be labeled as an aperture (aperture) in a VCSEL.

In the conventional VCSEL, a large amount of heat is generated in the element when a high current is applied due to the resonance characteristic, and thus, breakage of the element due to the application of the high current often occurs, and thus a low current capable of preventing the breakage of the element is injected. Therefore, the diffusion effect of the current injected into the electrode cannot be expected. As a result, the current emitted from the upper electrode disposed along the edge of the upper DBR cannot be sufficiently diffused and cannot uniformly pass through the current window of the central portion, thereby reducing efficiency.

KR10-2018-0015630 publication (WO 2016/198282) discloses an oxidized VCSEL having a peak wavelength of 850nm, and discloses a method of forming a plurality of oxide layers in various forms inside an upper DBR to improve the oxidized VCSEL. With this method, the nonuniformity of the reflectivity of the upper DBR is mainly caused during the manufacturing process, and a complicated problem is caused in the process of oxidation reprocessing or the like for generating a plurality of current windows.

In addition, the scheme of making the current emitted from the upper electrode uniformly pass through the current window of the central portion is as follows: a transparent ITO layer is formed on the entire upper DBR so that the current emitted from the ring electrode is uniformly supplied to the central portion through the ITO, but in this case, an expensive transparent electrode is required, and it is difficult to avoid a problem that the yield is extremely lowered in the ITO formation process.

Disclosure of Invention

Technical problem to be solved

The technical problem to be solved by the present invention is to provide a method capable of preventing damage to an upper DBR during a manufacturing process of an oxide Vertical Cavity Surface Emitting Laser (VCSEL).

Another technical problem to be solved by the present invention is to provide a method of manufacturing an oxidized type vertical cavity surface emitting laser by inducing a stable current flow and diffusion from an upper electrode of the vertical cavity surface emitting laser to a light emitting region of an active region.

Another technical problem to be solved by the present invention is to prevent damage of the upper DBR during oxidation of the oxidized vcsel and to induce stable current flow and diffusion from the upper electrode to the light emitting region while providing a highly conductive barrier layer transparent to the light source emitted by the oxidized vcsel.

Another technical problem to be solved by the present invention is to cover the upper DBR in the oxidized vertical cavity surface emitting laser to prevent damage of the upper DBR during oxidation and induce stable current flow and diffusion from the upper electrode to the light emitting region, while providing a thickness that significantly improves the efficiency of the vertical cavity surface emitting laser in a highly conductive barrier layer that is transparent to the light source emitted by the oxidized vertical cavity surface emitting laser.

Technical scheme

In order to solve the above problems, the present invention provides an oxidized Vertical Cavity Surface Emitting Laser (VCSEL) characterized in that a conductive current diffusion layer that transmits laser light having a peak wavelength of 860 ± 10nm (hereinafter referred to as "peak wavelength of 860 nm") is provided between an upper electrode and an upper distributed bragg reflector.

In the present invention, laser light is understood to have a wavelength with a full width at half maximum (FHWM) of less than 5 nm.

In the present invention, the current diffusion layer is preferably a non-oxidizing barrier (barrier) layer to cover the upper DBR layer during the oxidation of the vertical cavity surface emitting laser, thereby preventing damage during the oxidation.

In the embodiment of the present invention, the current diffusion layer may be an aluminum-free (Al free) layer containing no aluminum (Al) component to prevent oxidation by water vapor, and more preferably may be a conductive GaP layer having relatively high transparency to laser light having a peak wavelength of 860nm to improve the efficiency of the oxidized vertical cavity surface emitting laser when stacked.

In the present invention, the GaP layer may contain a metal or non-metal dopant in order to improve conductivity. The metal dopant may be, for example, magnesium (Mg), zinc (Zn), and the non-metal dopant may be carbon (C).

In the present invention, the current diffusion layer preferably has a thickness of 1 μm or more so that the current supplied to the active layer can be sufficiently diffused. If the thickness is small, the diffusion of current is insufficient, and thus the efficiency improvement of the oxidized VCSEL due to the introduction of the current diffusion layer is weak. In the present invention, the thickness of the current diffusion layer is preferably increased to a thickness (saturation thickness) at which there is no efficiency improvement effect due to saturation without increasing the thickness. In embodiments of the present invention, the saturation thickness may be 3 μm with a current window (current window) having a diameter of 10 μm.

In the invention, the oxidized vcsel may include a lower electrode, a substrate, an upper Distributed Bragg Reflector (Distributed Bragg Reflector), an active layer, an upper Distributed Bragg Reflector, an upper electrode, and an oxide layer.

In the present invention, the active layer of the vertical cavity surface emitting laser is an active layer capable of emitting light having a peak wavelength of 850 ± 10nm (hereinafter referred to as a peak wavelength of 850 nm). In one embodiment of the invention, the active layer may comprise GaAs quantum wells and AlGaAs quantum barrier layers.

In the present invention, the upper distributed bragg reflector and the lower distributed bragg reflector are respectively configured to reflect light emitted from the active layer upward and downward to resonate.

In the present invention, the upper DBR and the lower DBR may be DBRs in which a pair of reflective layers consisting of a high refractive layer and a low refractive layer are repeatedly stacked so as to be able to reflect light emitted from the active layer.

In the embodiment of the present invention, the lower DBR may use 30 or more pairs of n-DBRs, preferably 40 pairs of n-DBRs, so that light reflected by the active layer and the upper DBR can be substantially completely reflected, and in order to increase the light emission possibility, the upper DBR may be 5 to 10 pairs less than the lower DBR, preferably 20 to 25 pairs of p-DBRs.

In one embodiment of the present invention, the upper and lower distributed bragg reflectors may be Al having a high refractive index_xGa_1-xAs layer (0.8)<x<1) And Al having a low refractive index_yGa_1-yAs layer (0)<y<0.2) Distributed Bragg Reflectors (DBR) of an alternately repeating stacked structure.

In the present invention, the oxidized layer is composed of an oxidizing substance, and may be a layer in which a region oxidized for resonance and a non-oxidized region coexist. The oxide layer may be Al_zGa_1-zAs(0.95<z is less than or equal to 1) to be easily oxidized by high-temperature water vapor. The oxide layer is oxidized from the edge to the center portion and may be composed of a ring-shaped oxide layer and an inner center circular-shaped current window.

In the present invention, the diameter of the center circle of the oxide layer forming the current window needs to be narrow enough to emit laser light, and may preferably be 10 μm or less.

In the present invention, the oxide layer may be located on the upper portion of the active layer, preferably, may be located inside the upper p-DBR so as not to affect the active layer, may preferably be located between layers constituting the p-DBR, and more preferably may be located at the lower end of the upper p-BDR, for example, between the 1 st and 2 nd pairs of the lower end of the upper DBR, and may have a thickness of 30 to 100 nm.

In the embodiment of the invention, the oxidized vertical resonant cavity surface emitting laser can work under the current of 10-40 mA, preferably can work in the range of 25-35 mA, and most preferably can work in the range of 30-35 mA. When the current is 10mA or less, no laser light is generated, and when the current exceeds 40mA, no laser light having a peak wavelength of 860nm is generated due to the influence of heat generation.

In the present invention, the upper electrode may have a ring shape so as not to shield light emitted, and may be preferably selected from Indium Tin Oxide (ITO), ZnO, or AZO, and more preferably may be a multi-layer electrode composed of Au/Pt/Ti. In one embodiment, the thickness of the electrode may be about 2 μm or so.

In the present invention, the oxidized vertical cavity surface emitting laser may further include an antireflection layer to be able to prevent reflection of emitted light. The anti-reflection layer may be between the current diffusion layer and the upper electrode and cover the current diffusion layer. Also, the anti-reflection layer may be positioned at an uppermost portion of the oxide VCSEL and cover upper portions of the upper electrode and the current diffusion layer.

In an embodiment of the present invention, the anti-reflection layer may be made of SiN_xOr Si_xO_yThe composition can be grown to a thickness of about 100 to 500nm and used. The thickness is preferably 150 to 400nm, and more preferably 200 to 300 nm.

One aspect of the present invention provides a method of manufacturing an oxidized Vertical Cavity Surface Emitting Laser (VCSEL), wherein a GaP layer having a thickness of 1 μm or more is formed between an upper electrode and an upper DBR in an oxidized vertical cavity surface emitting laser having a peak wavelength of 860 nm.

Advantageous effects

The present invention provides a new barrier layer/current diffusion layer which can protect the upper DBR during oxidation, improve the current flow, and transmit light of an 860nm vcsel.

The oxidized Vertical Cavity Surface Emitting Laser (VCSEL) having a GaP barrier layer according to the present invention can improve electrode protection and current flow of an 860nm VCSEL having an oxidized aperture (oxidation aperture), achieve an improvement of light efficiency of up to 40%, and can confirm an optimized range of efficiency between a highly conductive substance used and the oxidized aperture of the VCSEL.

Drawings

Fig. 1 is a view showing a cross-sectional view of a conventional oxide VCSEL.

Fig. 2 (a) is a diagram showing an SEM image of a DBR breakage state occurring during oxidation, and fig. 2 (b) shows a shape of a current window (current window), a black stripe shape is a trench (recess) region, a middle region is a column region emitting light, and a brighter portion is an oxidized portion.

Fig. 3 shows the layer structure of a VCSEL emitting laser light of a peak wavelength of 860nm in which a highly conductive GaP barrier layer fabricated by an MOCVD system is used.

Fig. 4 (a) is a separated type cross-sectional view showing a layer structure of an oxidized VCSEL according to an embodiment of the present invention, and fig. 4 (b) shows a distribution of light emitted by an active layer and light of a resonant laser light (a local peak) is a resonance peak).

Fig. 5 is a graph showing the emission intensity (emission intensity) at 20mA for (a) a VCSEL without GaP of comparative example 1, (b) a VCSEL with GaP thickness of 1 μm of example 1, (c) a VCSEL with GaP thickness of 3 μm of example 2, and (d) a VCSEL with GaP thickness of 6 μm of example 3.

Fig. 6 shows a side SEM image, current injection path, and light emission pattern of VCSELs without GaP layers and 860nm VCSELs using GaP barrier layers of various thicknesses.

Fig. 7 is a graph showing curves of the VCSEL having the GaP layer thickness of 1 μm, 3 μm, and 6 μm according to comparative example 1 (general VCSEL) and examples 1 to 3 when a current of 0 to 50mA is applied, in which fig. 7 (a) is an I-V curve, and fig. 7 (b) is an I-L curve.

Fig. 8 is a graph showing current-voltage characteristics of a GaP layer and an AlGaAs layer.

Description of the reference numerals

100: oxidized Vertical Cavity Surface Emitting Laser (VCSEL)

110: lower electrode

120: substrate

130: lower DBR

140: active layer

150: upper DBR

160: GaP layer

170: upper electrode

180: oxide layer

Detailed Description

The present invention will be described in detail below with reference to examples. The following examples are intended to illustrate the invention, but not to limit it.