Surface emitting laser

Abstract

The present invention provides a surface emitting laser capable of high-speed operation. The surface emitting laser (100) comprises: a substrate (20); a lower contact layer (122) disposed on the substrate (20); a table (30) of a semiconductor layer, on which a lower reflector layer (123), an active layer (124), an upper reflector layer (125) and an upper contact layer (127) are sequentially stacked; an annular electrode (41) disposed on the upper contact layer (127); a light exit window (31) for emitting electric The laser is on the inner side of the circular ring of the pole (41), and the upper reflector layer (125) has: a first region (141), including the electrode (41) and the area directly below the light exit window (31); and a second region (142), including the periphery of the first region (141) within the table (30) on which the first region (141) is set and the area on the outside of the table (30), and the concentration of protons in the first region (141) is lower than the concentration of protons in the second region (142).

Description

Technical Field

[0001] The present invention relates to surface emitting lasers. Background Art

[0002] A vertical cavity surface emitting laser (VCSEL) is a laser that has two mirror layers and an active layer sandwiched by the mirror layers on a semiconductor substrate and emits light in a vertical direction relative to the substrate surface of the semiconductor substrate. In a surface emitting laser, a mesa is formed on the active layer and the mirror layer, and a portion of the mirror layer of the mesa is selectively oxidized to form an oxide layer, thereby forming a current limiting structure. It is disclosed that in such a surface emitting laser, by injecting protons into the mesa region, parasitic capacitance is reduced, and high-speed operation can be achieved (Non-Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-33210

[0006] Non-patent literature

[0007] Non-patent document 1: Chang, C., et al., "Parasitic effects and design considerations of oxide-implanted VCSELs." IEEE Photonics Technology Letters, vol. 13, No. 12, Dec. 2001, pp. 1274-1276, XP-001076755 Summary of the invention

[0008] Problems to be solved by the invention

[0009] Further high-speed operation is required for surface emitting lasers.

[0010] Technical means to solve problems

[0011] According to one viewpoint of the present embodiment, the surface emitting laser comprises: a substrate; a lower contact layer disposed on the substrate; a table of a semiconductor layer, on which a lower reflector layer, an active layer, an upper reflector layer, and an upper contact layer are sequentially stacked on the lower contact layer; an annular electrode disposed on the upper contact layer; and a light exit window, which emits laser light from the inner side of the annular ring of the electrode. Furthermore, the upper reflector layer comprises: a first region including the electrode and the light exit window directly below; and a second region including the periphery of the first region in the table on which the first region is disposed and a region outside the table, wherein the concentration of protons in the first region is lower than the concentration of protons in the second region.

[0012] Effects of the Invention

[0013] According to the surface emitting laser of the present disclosure, high-speed operation is possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a top view of a surface emitting laser according to an embodiment of the present disclosure.

[0015] Figure 2 is a cross-sectional view of a surface emitting laser according to an embodiment of the present disclosure.

[0016] Figure 3 is a top view of a surface emitting laser 201 for comparison.

[0017] Figure 4 is a cross-sectional view of a surface emitting laser 201 for comparison.

[0018] Figure 5 is a top view of a surface emitting laser 202 for comparison.

[0019] Figure 6 is a cross-sectional view of a surface emitting laser 202 for comparison.

[0020] Figure 7 is a top view of a surface emitting laser 203 for comparison.

[0021] Figure 8 is a cross-sectional view of a surface emitting laser 203 for comparison.

[0022] Fig. 9 It is a diagram showing the parasitic capacitance and cutoff frequency of a surface emitting laser.

[0023] Fig.10 This is a process diagram (1) of a method for manufacturing a surface emitting laser according to an embodiment of the present disclosure.

[0024] Fig.11 This is a process diagram (2) of a method for manufacturing a surface emitting laser according to an embodiment of the present disclosure.

[0025] Fig.12 This is a process diagram (3) of a method for manufacturing a surface emitting laser according to an embodiment of the present disclosure.

[0026] Fig.13 This is a process diagram (4) of a method for manufacturing a surface emitting laser according to an embodiment of the present disclosure.

[0027] Fig.14 This is a process diagram (5) of a method for manufacturing a surface emitting laser according to an embodiment of the present disclosure.

[0028] Fig.15This is a process diagram (6) of a method for manufacturing a surface emitting laser according to an embodiment of the present disclosure.

[0029] Explanation of symbols

[0030] 20 substrate

[0031] 30 countertops

[0032] 31 Light exit window

[0033] 32 slots

[0034] 41 p electrode

[0035] 42 Wiring

[0036] 43 p electrode pad

[0037] 51 n electrode

[0038] 52 Wiring

[0039] 53 n electrode pad

[0040] 100 Surface Emitting Lasers

[0041] 121 First lower DBR layer

[0042] 122 Lower contact layer

[0043] 123 Second lower DBR layer

[0044] 124 Active layer

[0045] 125 Upper DBR layer

[0046] 126 Current Limiting Structure

[0047] 126a Oxidation area

[0048] 126b Aperture area

[0049] 127 Upper contact layer

[0050] 128 High resistance area

[0051] 130 Insulation film

[0052] 131 first insulating film

[0053] 132 second insulating film

[0054] 133 Third insulating film

[0055] 141 First Area

[0056] 142 Second Area

[0057] 161, 162 Mask

[0058] 201, 202, 203 Surface emitting laser DETAILED DESCRIPTION

[0059] The following describes a method for implementing the method.

[0060] [Description of Embodiments of the Present Disclosure]

[0061] First, the embodiments of the present disclosure are listed and described. In the following description, the same or corresponding elements are given the same reference numerals, and the same description thereof will not be repeated.

[0062] [1] A surface emitting laser according to one embodiment of the present invention comprises a substrate, a lower contact layer arranged on the substrate, a table on which a semiconductor layer having a lower reflector layer, an active layer, an upper reflector layer, and an upper contact layer is sequentially stacked on the lower contact layer, an annular electrode arranged on the upper contact layer, and a light emitting window for emitting laser light from the inner side of the ring of the electrode, the upper reflector layer comprising a first region directly below the electrode and the light emitting window, a second region surrounding the first region within the table on which the first region is arranged, and a region outside the table, and the proton concentration of the first region is lower than the proton concentration of the second region.

[0063] This enables high-speed operation of the surface emitting laser.

[0064] [2] The upper reflector layer is doped with carbon as an impurity element, and in the second region, the concentration of protons is higher than the concentration of carbon.

[0065] This makes it possible to increase the resistance of the second region and realize high-speed operation of the surface emitting laser.

[0066] [3] In the above-mentioned first region, the concentration of protons is lower than the concentration of carbon.

[0067] This is because current needs to flow through the first region, and thus high resistance must be avoided.

[0068] [4] The proton concentration in the second region is 1×10 18 cm -3 Above and 1×10 20 cm -3 the following.

[0069] This makes it possible to increase the resistance of the second region and realize high-speed operation of the surface emitting laser.

[0070] [5] The surface emitting laser includes a first electrode pad connected to the upper contact layer and a second electrode pad connected to the lower contact layer, and the first electrode pad and the second electrode pad are provided on the second region.

[0071] By increasing the resistance of the portions below the first electrode pad and the second electrode pad, high-speed operation of the surface emitting laser can be achieved.

[0072] [Details of the embodiments of the present disclosure]

[0073] Hereinafter, one embodiment of the present disclosure will be described in detail, but the present embodiment is not limited thereto.

[0074] (Surface Emitting Laser)

[0075] based on Figure 1 and Figure 2 The surface emitting laser 100 of this embodiment will be described. Figure 1 is a top view of the surface emitting laser 100 of this embodiment. Figure 2 is along Figure 1 A cross-sectional view cut along the dashed line 1A-1B of FIG. The surface emitting laser 100 of the present embodiment has a first lower DBR (Distributed Bragg Reflector) layer 121, a lower contact layer 122, a second lower DBR layer 123, an active layer 124, an upper DBR layer 125, and an upper contact layer 127 formed in sequence on a substrate 20. In the present application, there is a case where the second lower DBR layer 123 or the first lower DBR layer 121 and the second lower DBR layer 123 are described as a lower reflector layer, and the upper DBR layer 125 is described as an upper reflector layer.

[0076] In the upper DBR layer 125, an oxidized region 126a is formed by oxidizing a portion of the multiple layers forming the upper DBR layer 125. By forming the oxidized region 126a, the unoxidized region becomes the aperture region 126b. Therefore, in the surface emitting laser, the current confinement structure 126 is formed by the oxidized region 126a and the aperture region 126b. The oxidized region 126a is formed by oxidizing from the peripheral portion of the mesa 30. The oxidized region 126a contains, for example, aluminum oxide (Al2O3) and has insulating properties, so it is not easy for current to flow through it compared to the aperture region 126b. Therefore, the aperture region 126b is easier for current to flow through than the oxidized region 126a, and becomes a current path. Therefore, by forming such a current confinement structure 126, efficient current injection can be performed. In the present embodiment, the diameter of the aperture region 126b is, for example, 7.5μm.

[0077] The substrate 20 is, for example, a semiconductor substrate made of semi-insulating gallium arsenide (GaAs). A buffer layer made of GaAs or AlGaAs may be provided between the substrate 20 and the first lower DBR layer 121 .

[0078] The first lower DBR layer 121, the second lower DBR layer 123, and the upper DBR layer 125 are made of, for example, Al x Ga 1－x As (x = 0.16) and Al y Ga 1－y As (y = 0.9) is alternately stacked with an optical film thickness of λ / 4. The first lower DBR layer 121 is an i-type semiconductor layer, which is not doped with impurity elements. The second lower DBR layer 123 is an n-type semiconductor layer, for example, with a thickness of 7×10 17 cm -3 Above and 2×10 18 cm -3 The upper DBR layer 125 is a p-type semiconductor layer, for example, with a concentration of 1×10 18 cm -3 Above and 1×10 19 cm -3 Zinc (Zn) is doped as an impurity element at the following concentrations.

[0079] The lower contact layer 122 is made of, for example, n-type Al with a thickness of 400 nm. x Ga 1－x As (x = 0.1) is formed with 3×10 18 cm -3 The upper contact layer 127 is, for example, made of p-type Al with a thickness of 100 nm. x Ga 1－x As (x = 0.16) is formed with 1×10 19 cm -3 The concentration of Zn is doped as an impurity element.

[0080] The active layer 124 has, for example, alternately stacked In y Ga 1－y As layer (y = 0.107) and Al x Ga 1－x As layer (x = 0.3) formed of multiple quantum well (MQW: Multiple Quantum Well: multiple quantum well) structure, has optical gain. In addition, the substrate 20, the first lower DBR layer 121, the lower contact layer 122, the second lower DBR layer 123, the active layer 124, the upper DBR layer 125, and the upper contact layer 127 can also be formed of compound semiconductors other than the above.

[0081] The mesa 30 is formed by the second lower DBR layer 123, the active layer 124, the upper DBR layer 125, and the upper contact layer 127. Specifically, the second lower DBR layer 123, the active layer 124, the upper DBR layer 125, and the upper contact layer 127 around the area where the mesa 30 is formed are removed to form a groove 32, thereby forming the mesa 30 of the semiconductor layer. The height of the mesa 30 is, for example, greater than 4.5 μm and less than 5.0 μm, and the width of the upper surface is, for example, 30 μm. The active layer 124, the upper DBR layer 125, and the upper contact layer 127 are formed in the central part of the mesa 30, and the high resistance region 128 is formed in the peripheral part of the mesa 30.

[0082] An insulating film 130 is formed on the semiconductor layer including the upper surface and side surfaces of the mesa 30. The insulating film 130 is formed of silicon nitride (SiN) or silicon oxynitride (SiON). In this embodiment, the insulating film 130 is formed of a first insulating film 131, a second insulating film 132, and a third insulating film 133.

[0083] The p-electrode 41 is formed on the upper contact layer 127 on the upper surface of the mesa 30, and the n-electrode 51 is formed on the lower contact layer 122 exposed on the bottom surface of the groove 32. The p-electrode 41 on the upper surface of the mesa 30 is provided with a wiring 42 connected to the p-electrode pad 43, and the n-electrode 51 on the bottom surface of the groove 32 is provided with a wiring 52 connected to the n-electrode pad 53.

[0084] In this embodiment, the p-electrode 41 is formed of a film in which Ti / Pt / Au are stacked in this order. The n-electrode 51 is formed of, for example, a stacked film of gold (Au), germanium (Ge), and nickel (Ni). The wiring 42, the wiring 52, the p-electrode pad 43, and the n-electrode pad 53 are formed of, for example, a metal such as Au.

[0085] In the surface emitting laser of the present embodiment, a bonding wire or the like not shown is connected to the p-electrode pad 43 and the n-electrode pad 53, and current is injected into the surface emitting laser. The light emitted from the active layer 124 by the injection of current oscillates through the first lower DBR layer 121, the second lower DBR layer 123, and the upper DBR layer 125 forming the resonator, and is emitted from the light exit window 31 as laser light in the direction indicated by the dotted arrow. The light exit window 3 is formed on the inner side of the p-electrode 41 formed in a circular ring shape on the upper surface of the table 30. In the present embodiment, the diameter of the p-electrode 41 is larger than the diameter of the aperture region 126b.

[0086] In the present embodiment, the high resistance region 128 is not formed in the region directly below the p-electrode 41 and the light exit window 31, but is formed in the region other than the region directly below the p-electrode 41 and the light exit window 31. In the present application, in the upper DBR layer 125, the region directly below the p-electrode 41 and the light exit window 31 is described as the first region 141, and the peripheral portion of the mesa 30 other than the first region 141, the region directly below the p-electrode pad 43 and the n-electrode pad 53, etc. are described as the second region 142. Therefore, the high resistance region 128 is formed in the second region 142, and the active layer 124, the upper DBR layer 125, and the upper contact layer 127 are formed in the first region 141.

[0087] The high resistance region 128 is formed by injecting protons (H) into the upper DBR layer 125. + ) is formed. Therefore, the proton concentration of the second region 142 is higher than that of the first region 141. The proton concentration of the second region 142 is 1×10 18 cm -3 Above and 1×10 20 cm -3 In addition, the upper DBR layer 125 is 6×10 17 cm -3 ~4×10 18 cm -3 The concentration of C (carbon) is doped as an impurity element at a concentration of 1.1777 W / m2. Therefore, in the second region 142, the concentration of protons is higher than the concentration of C, and in the first region 141, the concentration of protons is lower than the concentration of C.

[0088] (Range and Characteristics of High Resistance Region 128)

[0089] Next, the surface emitting lasers 201 to 203 having different high resistance regions 128 were studied.

[0090] like Figure 3 and Figure 4 As shown, the surface emitting laser 201 has a high resistance region 128 formed in the region except for the entire mesa 30 and the vicinity of the outer side of the groove 32 around the mesa 30. In addition, Figure 3 is a top view of the surface emitting laser 201, Figure 4 is along Figure 3 A cross-sectional view of the device cut off by the single-dot chain line 3A-3B.

[0091] like Figure 5 and Figure 6 As shown, the surface emitting laser 202 has a high resistance region 128 formed in the region except for the region directly below the p-electrode 41 and the light exit window 31 and the region directly below the p-electrode pad 43 and the n-electrode pad 53. Figure 5 is a top view of the surface emitting laser 202, Figure 6 is along Figure 5 A cross-sectional view of the device cut off by the single-dot chain line 5A-5B.

[0092] like Figure 7 and Figure 8 As shown, the surface emitting laser 203 has a high resistance region 128 formed in the region except for the entire mesa 30 and the vicinity of the outer side of the groove 32 including the periphery of the mesa 30, and the region directly below the p-electrode pad 43 and the n-electrode pad 53. Figure 7 is a top view of the surface emitting laser 203, Figure 8 is along Figure 7 A cross-sectional view of the device cut off by the single-dot chain line 7A-7B.

[0093] Fig. 9 2 is a diagram showing parasitic capacitance and cutoff frequency in surface emitting lasers 100, 201, 202, and 203. The parasitic capacitance of the surface emitting laser 100 in this embodiment is about 340 fF, and the cutoff frequency is about 19.6 GHz. In contrast, the parasitic capacitance of the surface emitting laser 201 is about 420 fF, and the cutoff frequency is about 15.2 GHz. In addition, the parasitic capacitance of the surface emitting laser 202 is about 550 fF, and the cutoff frequency is about 11.8 GHz. The parasitic capacitance of the surface emitting laser 203 is about 630 fF, and the cutoff frequency is about 10.1 GHz.

[0094] Therefore, the surface emitting laser 100 in the present embodiment has a higher cutoff frequency than the surface emitting lasers 201 , 202 , and 203 , and thus can operate at a high speed.

[0095] (Method for manufacturing surface-emitting laser)

[0096] Next, based on Figure 10 to Figure 15 A method for manufacturing the surface emitting laser in this embodiment will be described.

[0097] First, if Fig.10As shown, a first lower DBR layer 121, a lower contact layer 122, a second lower DBR layer 123, an active layer 124, an upper DBR layer 125, and an upper contact layer 127 are epitaxially grown in sequence on a wafer-state substrate 20. Specifically, the semiconductor layers of the first lower DBR layer 121, the lower contact layer 122, the second lower DBR layer 123, the active layer 124, the upper DBR layer 125, and the upper contact layer 127 are formed by a metal organic vapor phase growth (MOCVD: Metal Organic Chemical Vapor Deposition: metal organic chemical vapor deposition) method or a molecular beam epitaxy (MBE: Molecular Beam Epitaxy: molecular beam epitaxy) method or the like.

[0098] In addition, the upper DBR layer 125 includes Al for forming the oxidized region 126a of the current confinement structure 126. x Ga 1－x As layer (0.95≤x≤1.0) Thereafter, the first insulating film 131 is formed on the upper contact layer 127 by, for example, a plasma CVD (Chemical Vapor Deposition) method.

[0099] Next, if Fig.11 As shown, a mask 161 is formed on the first insulating film 131, and protons are injected to form a high resistance region 128. The ion injection depth is, for example, 3.5 μm or less, and the high resistance region 128 is formed by injecting protons into the upper contact layer 127, the upper DBR layer 125, and the active layer 124 in the region where the mask 161 is not provided. In addition, protons are not injected into the portion covered by the mask 161.

[0100] Next, if Fig.12 As shown, after the mask 161 is removed by an organic solvent or the like, another mask 162 is formed. The mask 162 is larger than the mask 161 and covers the region where protons are not injected and a portion of the high resistance region 128. Then, in the region where the mask 162 is not formed, the high resistance region 128 and the second lower DBR layer 123 are removed by dry etching until the lower contact layer 122 is exposed, thereby forming a groove 32. Thus, the terrace 30 is formed. In this dry etching, for example, an inductively coupled plasma reactive ion etching (ICP-RIE: Inductively Coupled Plasma Reactive Ion Etching) device is used. Then, the mask 162 is removed by an organic solvent or the like.

[0101] Next, if Fig.13As shown, for example, by heating to a temperature of about 400° C. in a water vapor atmosphere, the Al in the upper DBR layer 125 is oxidized from the side surface of the mesa 30. x Ga 1－x As layer (0.9≤x≤1.0) is formed to form an oxidized region 126a. The oxidized region 126a is formed by adjusting the heating time until the aperture region 126b of the unoxidized portion surrounded by the oxidized region 126a reaches a predetermined size. Thereafter, dry etching is performed to remove from the upper contact layer 127 to the first lower DBR layer 121, thereby forming a groove for element isolation (not shown) with a depth of, for example, 8.0 μm.

[0102] Next, if Fig.14 As shown, the second insulating film 132 is formed by, for example, a plasma CVD method, and further, openings are formed in the second insulating film 132 at the upper surface portion of the mesa 30 and the bottom surface portion of the groove 32 .

[0103] Next, if Fig.15 As shown, a third insulating film 133 is formed, and an opening is formed in a part of the upper surface portion of the mesa 30 and the bottom surface portion of the groove 32 in the third insulating film 133. Then, by forming a resist pattern and forming a film by vacuum evaporation, a p-electrode 41 is formed on the upper contact layer 127, and an n-electrode 51 is formed on the lower contact layer 122. Then, an ohmic contact is obtained by performing a heat treatment.

[0104] Thereafter, the wiring 42 is formed on the p-electrode 41 and the third insulating film 133, and the wiring 52 is formed on the n-electrode 51 and the third insulating film 133 by plating or the like. Thus, the p-electrode pad 43 electrically connected to the p-electrode 41 via the wiring 42 and the n-electrode pad 53 electrically connected to the n-electrode 51 via the wiring 52 are formed. Thereafter, the wafer-like substrate 20 is divided to form a chip-shaped surface emitting laser.

[0105] Through the above-described steps, the surface emitting laser of the present embodiment can be manufactured.

[0106] Although the embodiments have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope described in the claims.

Claims

1. A surface emitting laser, comprising: substrate; A lower contact layer is disposed on the substrate; a mesa of a semiconductor layer, wherein a lower reflector layer, an active layer, an upper reflector layer and an upper contact layer are sequentially stacked on the lower contact layer; a ring-shaped electrode disposed on the upper contact layer; and The light exit window emits the laser light from the inner side of the electrode ring. The upper reflector layer comprises: a first region including the electrode and directly below the light exit window; and a second region including the periphery of the first region in the table on which the first region is disposed and a region outside the table. The concentration of protons in the first region is lower than the concentration of protons in the second region, The upper mirror layer is doped with carbon as an impurity element, In the second region, the concentration of protons is higher than that of carbon. In the first region, the concentration of protons is lower than the concentration of carbon.

2. The surface emitting laser according to claim 1, wherein The proton concentration in the second region is 1×10 18 cm -3 Above and 1×10 20 cm -3 the following.

3. The surface emitting laser according to claim 1 or 2, wherein: The surface emitting laser has: A first electrode pad connected to the upper contact layer; and A second electrode pad is connected to the lower contact layer, The first electrode pad and the second electrode pad are disposed on the second region.

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