Vertical cavity surface emitting laser and method for manufacturing the same

Abstract

The present application relates to the field of semiconductor laser, and particularly relates to a vertical cavity surface emitting laser and a preparation method thereof, the laser comprising a substrate; a buffer structure covering a surface of a germanium / silicon or germanium substrate, the buffer structure comprising: a nucleation layer in contact with the surface of the substrate, for providing nucleation points on the surface of the substrate; a first buffer layer covering the nucleation layer, for merging a three-dimensional island structure of the nucleation layer and forming a surface without anti-phase domains; a second buffer layer covering the first buffer layer, for providing a flat surface; a resonant cavity arranged on the buffer structure, comprising: a first Bragg mirror arranged on the second buffer layer, for reflecting light in the laser to form laser oscillation; a second Bragg mirror separated from the first Bragg mirror by an active layer, for reflecting light in the laser to form laser oscillation; the active layer for providing gain to generate laser; and an electrode arranged in the resonant cavity or in contact with the substrate, for current injection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor lasers, in particular to a vertical cavity surface emitting laser and a preparation method thereof. BACKGROUND

[0002] The resonant cavity of the vertical cavity surface emitting laser is not prepared by edge-emitting end face cleavage, but is formed by Bragg reflector, which makes the laser emit along the epitaxial direction of the material, that is, perpendicular to the substrate direction. Due to its advantages of high beam quality, single longitudinal mode lasing, low threshold current density, on-chip testing, easy two-dimensional array integration and the like, the vertical cavity surface emitting laser is widely used in optical interconnection, optical communication, face recognition, laser radar and the like.

[0003] The Bragg reflector (DBR) is generally composed of two kinds of media with different refractive indexes and optical thickness of one-fourth of the central wavelength of reflection, wherein the greater the refractive index difference between the two kinds of materials and the more the period logarithm, the higher the reflectivity. Because the volume of the active region of the VCSEL is small, the device has a high requirement for the reflectivity of the DBR. Under the current epitaxial material system, dozens or even hundreds of pairs are generally required, which makes the physical thickness of the VCSEL device several microns to tens of microns. In this case, the wafer of the epitaxial wafer will be warped due to the lattice mismatch stress and thermal stress introduced by the growth of the DBR. Such warping will lead to uneven growth of the entire wafer surface, and will also affect the subsequent photolithography process, so that the device processing batch is increased, the yield is reduced, and it is difficult to manufacture large array size devices.

[0004] Because the lattice constants of AlAs and GaAs are close, the refractive index difference is large, and the AlGaAs current limiting layer has a mature wet oxidation process, the GaAs-based VCSEL industry occupies the main market of VCSEL. However, there is still a 0.14% deviation in the lattice constants of AlAs and GaAs, and the stress accumulated in the several-micron AlGaAs DBR during the growth process leads to the warping of the GaAs-based VCSEL epitaxial wafer. In addition, the larger the size of the substrate, the more obvious the wafer warping, and these factors all limit the large-scale production of GaAs-based VCSEL. SUMMARY

[0005] Based on this, the present application provides a vertical cavity surface emitting laser and a preparation method thereof, which can improve the wafer warping problem of the GaAs-based vertical cavity surface emitting laser epitaxial wafer.

[0006] According to an aspect of the present application, a vertical cavity surface emitting laser is provided, comprising:

[0007] a substrate, the substrate being a germanium substrate or a germanium / silicon substrate;

[0008] a buffer structure covering the surface of the substrate, comprising:

[0009] a nucleation layer, in contact with the substrate surface, for providing nucleation sites on the surface of the substrate;

[0010] a first buffer layer, overlying the nucleation layer, for merging the three-dimensional island structure of the nucleation layer and forming a surface without anti-phase domains;

[0011] a second buffer layer, overlying the first buffer layer, for providing a flat surface;

[0012] a resonant cavity, disposed on the buffer structure, comprising:

[0013] a first Bragg mirror, disposed on the second buffer layer, for reflecting light within the laser to form a laser oscillation;

[0014] a second Bragg mirror, separated from the first Bragg mirror by an active layer, for reflecting light within the laser to form a laser oscillation;

[0015] an active layer, for providing gain to generate a laser;

[0016] an electrode, disposed within the resonant cavity or in contact with the substrate, for current injection.

[0017] According to an embodiment of the present application, the substrate is one of semi-insulating, n-doped or p-doped.

[0018] The substrate is either off-angle or on-angle.

[0019] According to an embodiment of the present application, the nucleation layer and the first buffer layer are III-V compound with lattice constant close to that of germanium.

[0020] The second buffer layer is GaAs material.

[0021] According to an embodiment of the present application, the vertical cavity surface emitting laser further comprises an electrode contact layer, in the case that the electrode is disposed within the resonant cavity, the electrode is disposed on the electrode contact layer, the electrode contact layer is in contact with the first Bragg mirror or the second Bragg mirror, for forming ohmic contact with the electrode.

[0022] According to an embodiment of the present application, the resonant cavity further comprises a current confinement layer, disposed on one side or both sides of the active layer, for forming a current confinement aperture to confine current injected into the active layer.

[0023] The current confinement aperture has a size of 1 to 20 microns.

[0024] According to an embodiment of the present application, the active layer is quantum dot or quantum well material composed of III-V compound;

[0025] The active layer has a light emission wavelength of 700-1550 nm;

[0026] The quantum well or quantum dot layer has a number of 1-30;

[0027] The active layer has an optical thickness of 1-10 times the central wavelength of the laser.

[0028] According to an embodiment of the present application, the first Bragg mirror and the second Bragg mirror are both composed of two different components of AlGaAs, each layer having an optical thickness of 0.25λ;

[0029] The first Bragg mirror and the second Bragg mirror are semi-insulating Bragg mirrors or doped Bragg mirrors;

[0030] The doped Bragg mirror is of modulation doping or modulation doping combined with δ doping;

[0031] The p-type dopant source is beryllium or carbon, the n-type dopant source is silicon, and the gradually changing component has a thickness of 0-30 nm.

[0032] According to another aspect of the present application, a method for manufacturing the vertical cavity surface emitting laser is provided, comprising:

[0033] Growing a buffer structure on a substrate;

[0034] Growing a first Bragg mirror on the buffer structure;

[0035] Growing an active layer on the first Bragg mirror by co-evaporation and migration enhancement;

[0036] Growing a second Bragg mirror on the active layer;

[0037] Etching the laser;

[0038] Manufacturing electrodes on the electrode contact layer of the substrate or the first Bragg mirror, and on the electrode contact layer of the second Bragg mirror.

[0039] According to an embodiment of the present application, the method further comprises:

[0040] Growing a current limiting layer on the first Bragg mirror and / or on the active layer;

[0041] Obtaining an oxidation aperture on the current limiting layer by wet oxidation.

[0042] According to the embodiment of the present application, the growth method of the buffer structure comprises:

[0043] The substrate is pretreated;

[0044] A nucleation layer is grown;

[0045] A first buffer layer is grown;

[0046] A second buffer layer is grown.

[0047] According to the embodiment of the present application, the pretreatment of the substrate comprises:

[0048] The substrate is subjected to high-temperature annealing treatment in a V-atom-free atmosphere, and the substrate forms a double-atom step surface;

[0049] The annealing temperature is 550-750 DEG C, and the annealing time is 20-40 min.

[0050] Beneficial effects:

[0051] In order to improve the wafer warping problem of a GaAs-based vertical cavity surface emitting laser epitaxial wafer, the present application uses germanium, germanium / silicon substrate instead of the traditional GaAs substrate, and has a buffer structure with a three-layer structure of a nucleation layer, a first buffer layer and a second buffer layer, which can obtain a non-inversion domain, high crystal quality and GaAs buffer structure comparable to GaAs substrate. Since the germanium lattice constant is between GaAs and AlAs, growing multiple pairs of AlGaAs Bragg reflectors on the germanium substrate can obtain stress compensation, thereby improving the critical thickness of the AlGaAs Bragg reflector, the interface roughness and the reflectivity of the Bragg reflector under the same period, and providing the possibility for large-scale production of long-wavelength VCSELs.

[0052] The germanium substrate used in the present application has higher mechanical strength, larger wafer size, lower substrate price and fewer defects compared with the traditional GaAs substrate, so that the use of the germanium substrate to prepare the vertical cavity surface emitting laser can improve the wafer warping problem of the existing GaAs-based VCSEL due to the excessive epitaxial thickness, can be produced on a larger size substrate, reduces the device production cost, improves the device yield and manufactures larger VCSEL arrays.

[0053] Silicon and germanium are commonly used in transistor manufacturing and are fully compatible with CMOS technology. Therefore, integrating the germanium-based and germanium / silicon-based VCSEL with microelectronic devices to solve the problems such as power consumption and transmission rate of integrated circuits is a path to realize optoelectronic interconnection. Moreover, compared with GaAs, silicon and germanium are non-toxic, and the recycling technology is relatively mature, which makes the germanium-based and germanium / silicon-based VCSEL industry more environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 Preparation flowchart of vertical cavity surface emitting laser of the embodiment of the present application;

[0055] Figure 2 Structure diagram of germanium-based vertical cavity surface emitting quantum dot laser of sample 1 in the embodiment of the present application;

[0056] Figure 3 Structure diagram of germanium / silicon-based vertical cavity surface emitting quantum well laser of sample 2 in the embodiment of the present application;

[0057] Figure 4 Structure diagram of germanium-based vertical cavity surface emitting quantum well laser of sample 3 in the embodiment of the present application;

[0058] Figure 5 Structure diagram of germanium-based vertical cavity surface emitting quantum well laser of sample 4 in the embodiment of the present application;

[0059] Figure 6 Structure diagram of germanium-based vertical cavity surface emitting quantum well laser of sample 5 in the embodiment of the present application;

[0060] Figure 7 Structure diagram of germanium-based vertical cavity surface emitting quantum well laser of sample 6 in the embodiment of the present application.

[0061] In the figure:

[0062] 1 - substrate;

[0063] 2 - nucleation layer;

[0064] 3 - first buffer layer;

[0065] 4 - second buffer layer;

[0066] 5 - first Bragg mirror;

[0067] 6 - second Bragg mirror;

[0068] 7 - first electrode;

[0069] 8 - first current confinement layer;

[0070] 9 - active layer;

[0071] 10 - second current confinement layer;

[0072] 11 - second electrode;

[0073] 12 - second contact layer;

[0074] 13 - first contact layer. DETAILED DESCRIPTION

[0075] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to specific embodiments and with reference to the drawings.

[0076] Because the lattice constants of AlAs and GaAs are close, the refractive index difference is large, and AlGaAs has a mature wet oxidation process, the GaAs-based VCSEL industry currently occupies the main market of VCSEL. However, there is still a 0.14% deviation in the lattice constants of AlAs and GaAs, and the stress is continuously accumulated in the AlGaAs DBR in the growth process in the order of several microns, resulting in the warping of the GaAs-based VCSEL epitaxial wafer. In addition, the size of the substrate also affects the degree of wafer warping, so the largest substrate currently used by commercial GaAs-based VCSEL is 6 inches. These factors all limit the large-scale production of GaAs-based VCSEL. In addition, it is difficult to mass-produce VCSELs above 1100 nm on a GaAs substrate, because long-wavelength VCSELs require thicker DBR structures to match λ / 4, and the increase in epitaxial thickness will exacerbate wafer warping.

[0077] In addition, compared with traditional edge-emitting lasers, VCSELs have the properties of high-quality light beams, no need for cleaving to prepare cavity surfaces, on-chip testing, and easy two-dimensional array integration, and are considered to be suitable light sources for silicon-based optoelectronic integration technology to cope with the explosive growth of traffic in the big data era and the failure of traditional Moore's law. However, the traditional GaAs wafer will introduce arsenic contamination in the CMOS process, and GaAs-based VCSELs cannot be integrated with traditional silicon-based microelectronic devices in a mature CMOS process line.

[0078] Therefore, it is necessary to provide a vertical cavity surface emitting laser and a preparation method thereof, which can improve the problem of warping of the traditional GaAs-based vertical cavity surface emitting laser epitaxial wafer.

[0079] According to the overall inventive concept of one aspect of the present application, a vertical cavity surface emitting laser is provided, which comprises a substrate 1, a buffer structure, a resonant cavity and an electrode.

[0080] The substrate 1 is a germanium substrate 1 or a germanium / silicon substrate 1.

[0081] The buffer structure is covered on the surface of the substrate 1 and comprises a nucleation layer 2, a first buffer layer 3 and a second buffer layer 4. The nucleation layer 2 is in contact with the surface of the substrate 1 and is used to provide nucleation points on the surface of the substrate 1; the first buffer layer 3 is covered on the nucleation layer 2 and is used to form a surface without anti-phase domains; and the second buffer layer 4 is covered on the first buffer layer 3 and is used to provide a flat surface.

[0082] The resonant cavity is arranged on the buffer structure and comprises a first Bragg mirror 5, a second Bragg mirror 6 and an active layer 9.

[0083] The electrode is arranged in the resonant cavity or in contact with the substrate 1 and is used for current injection.

[0084] In order to improve the wafer warping problem of a conventional GaAs-based vertical cavity surface emitting laser epitaxial wafer, the germanium or germanium / silicon substrate 1 is used to replace the conventional GaAs substrate 1, the buffer structure has a three-layer structure of a nucleation layer, a first buffer layer and a second buffer layer, and a GaAs buffer structure with no reverse domain, high crystal quality and comparable GaAs substrate 1 can be obtained. Since the germanium lattice constant is between GaAs and AlAs, a plurality of pairs of AlGaAs Bragg mirrors can be grown on the germanium substrate 1 to obtain stress compensation, thereby improving the critical thickness of the AlGaAs Bragg mirror, the interface roughness and the reflectivity of the Bragg mirror under the same period, and providing the possibility for large-scale production of long-wavelength VCSELs.

[0085] The germanium or germanium / silicon substrate 1 used in the application has higher mechanical strength, larger wafer size, lower price and fewer defects than the conventional GaAs substrate 1, so that the use of the germanium or germanium / silicon substrate 1 to prepare the vertical cavity surface emitting laser can improve the wafer warping problem caused by the excessive epitaxial thickness of the existing GaAs-based VCSEL, can be produced on a larger size substrate 1, reduces the device production cost, improves the device yield and manufactures larger VCSEL arrays.

[0086] Silicon and germanium are commonly used in transistor manufacturing and are fully compatible with CMOS technology. Therefore, the integration of the germanium-based or germanium / silicon-based VCSEL and microelectronic devices to solve the problems such as power consumption and transmission rate of integrated circuits is a path to realize optoelectronic interconnection. And compared with GaAs, silicon and germanium are non-toxic, and the recycling technology is very mature, which makes the germanium-based or germanium / silicon-based VCSEL industry very friendly to the environment.

[0087] The buffer structure is arranged on the substrate 1 and is used for eliminating reverse domains and dislocations, obtaining a smooth surface and a GaAs with high crystal quality.

[0088] According to the embodiment of the application, the substrate 1 is one of semi-insulating, n-type doped or p-type doped, and the substrate 1 can be a germanium substrate 1 or a germanium / silicon substrate 1 with or without an offset angle.

[0089] Based on the characteristic that VCSEL preparation does not need cavity surface cleavage, in the application, GaAs-based VCSEL is prepared by using a bias angle germanium substrate or a bias angle germanium / silicon substrate. The advantage is that a double-atom step can be easily obtained on the substrate surface by annealing pretreatment, the difficulty of heteroepitaxy between the polar mismatch materials is greatly reduced without changing the device preparation process, and the generation of the reverse phase domain at the interface can be completely suppressed.

[0090] According to the embodiment of the application, the nucleation layer 2 and the first buffer layer 3 are III-V compound with a lattice constant close to that of germanium.

[0091] The second buffer layer 4 is GaAs material.

[0092] According to the embodiment of the application, the nucleation layer 2 and the first buffer layer 3 can be GaAs, AlAs, InGaP, InAlP material.

[0093] According to the embodiment of the application, the vertical cavity surface emitting laser further comprises an electrode contact layer, in the case that an electrode is arranged in the resonant cavity, the electrode is arranged on the electrode contact layer, the electrode contact layer is in contact with the first Bragg mirror 5 or the second Bragg mirror 6, and is used to form ohmic contact with the electrode.

[0094] According to the embodiment of the application, the first Bragg mirror 5 and the second Bragg mirror 6 are both composed of two different components AlGaAs, and each layer has an optical thickness of 0.25λ.

[0095] The first Bragg mirror 5 and the second Bragg mirror 6 can be semi-insulating or doped.

[0096] The doped Bragg mirror can be modulation doped or a combination of modulation doped and delta doped.

[0097] The p-type doping source can be beryllium or carbon, the n-type doping source can be silicon, and the thickness of the component gradient can be 0-30nm.

[0098] According to the embodiment of the application, the first Bragg mirror 5 and the second Bragg mirror 6 further comprise a current diffusion layer, the current diffusion layer is added with an optical thickness of an integer multiple of λ in the GaAs layer in the Bragg mirror, and is used as a channel for current injection into the active layer 9, so as to reduce the resistance of the first Bragg mirror 5 and the second Bragg mirror 6.

[0099] According to the embodiment of the application, the AlGaAs with low Al component is increased according to the decrease of the working wavelength of the laser, so as to reduce the loss caused by the optical absorption of AlGaAs, and the AlGaAs with high Al component is lower than the current limiting layer AlGaAs.

[0100] According to the embodiment of the present application, the resonant cavity further comprises a current limiting layer arranged on one side or both sides of the active layer 9, for forming a current limiting aperture to limit the current injected into the active layer 9.

[0101] The size of the current limiting aperture is 1-20 microns.

[0102] According to the embodiment of the present application, the aperture of the current limiting layer is an oxidation aperture, and the current limiting layer of the oxidation aperture can be multi-layered, which can be divided into an oxide aperture layer and a deep oxidation layer, both of which are AlGaAs materials, wherein the oxide aperture layer has a higher Al component than the deep oxidation layer.

[0103] According to the embodiment of the present application, the active layer 9 is quantum dot or quantum well material composed of III-V compound; the active layer 9 has a light emitting wavelength of 700-1550 nm; the number of quantum well and quantum dot layers is 1-30; and the optical thickness of the active layer 9 is 1-10 times of the wavelength.

[0104] According to the embodiment of the present application, the material system of the active layer 9 can be AlGaAs / GaAs, InGaAs / GaAs, InAlGaP / GaAs, InGaAsN / GaAs, InGaAsSb / GaAs, etc.

[0105] Figure 1 The figure shows the preparation process of the vertical cavity surface emitting laser according to the embodiment of the present application.

[0106] As Figure 1 shown, according to another aspect of the present application, a method for preparing a vertical cavity surface emitting laser is provided, comprising:

[0107] S100: growing a buffer structure on a substrate 1;

[0108] S200: growing a first Bragg reflector 5 on the buffer structure;

[0109] S300: growing an active layer 9 on the first Bragg reflector 5 by co-evaporation and migration enhancement;

[0110] S400: growing a second Bragg reflector 6 on the active layer 9;

[0111] S500: etching the laser;

[0112] S600: preparing electrodes on the electrode contact layer of the substrate 1 or the first Bragg reflector 5, and on the electrode contact layer of the second Bragg reflector 6.

[0113] According to an embodiment of the present application, the etching in the laser in S500 comprises: etching the mesa on the laser material in sequence, and the mesa of the laser is prepared by dry etching or wet etching.

[0114] According to an embodiment of the present application, before S500, it can further comprise: growing a current confinement layer on the first Bragg reflector 5 and / or the active layer 9.

[0115] The oxide aperture is obtained on the current confinement layer by wet oxidation.

[0116] According to an embodiment of the present application, the electrode in S600 comprises the first electrode 7 and the second electrode 11, and the electrode is prepared by sputtering, electron beam evaporation or thermal evaporation.

[0117] According to an embodiment of the present application, after growing the current confinement layer, it can further comprise: preparing a passivation layer and a light exit.

[0118] According to an embodiment of the present application, in S100, the growth method of the buffer structure comprises:

[0119] S101: pretreating the substrate 1;

[0120] S102: growing a nucleation layer 2;

[0121] S103: growing a first buffer layer 3;

[0122] S104: growing a second buffer layer 4.

[0123] According to an embodiment of the present application, in S101, the pretreatment of the substrate 1 comprises:

[0124] high-temperature annealing the substrate 1 in an atmosphere without group V atoms, so that the substrate 1 forms a double-atom step surface; wherein the annealing temperature is 550-750 ℃, and the annealing time is 20-40 min.

[0125] According to an embodiment of the present application, S102 comprises: growing the nucleation layer 2 at a low rate by using a migration enhanced epitaxy method, the preset layer of the nucleation layer 2 is group V or group III atoms, the growth temperature is 200-400 ℃, the growth rate is 0.1-0.4 μm / h, the V / III value is 10-30, and the thickness is 10-100 atomic monolayers.

[0126] According to an embodiment of the present application, S103 comprises: growing the first buffer layer 3 at a low rate and a low V / III value by using a co-evaporation epitaxy method, the growth temperature of the first buffer layer 3 is 300-500 ℃, the growth rate is 0.1-0.4 μm / h, the V / III value is 5-20, and the thickness is 50-300 nm.

[0127] According to the embodiment of the present application, S104 comprises: growing the second buffer layer 4 by using the co-evaporation method, the growth temperature is 580-640℃, the growth rate is 0.5-2.0 μm / h, the V / III value is 10-25, and the thickness is 300-1000 nm.

[0128] According to the embodiment of the present application, in S200, growing the first Bragg mirror 5 on the buffer structure comprises: the AlGaAs layer growth temperature is 580-630℃, the growth rate is 0.2-1.0 μm / h, and the V / III value is 10-40.

[0129] According to the embodiment of the present application, S200-S400 further comprise growing the electrode contact layer, the electrode contact layer can comprise the first contact layer 13 and the second contact layer 12, the first contact layer 13 is used to separate the first electrode 7 and the first Bragg mirror 5 or the second Bragg mirror 6, the second contact layer 12 is used to separate the second electrode 11 and the second Bragg mirror 6, the GaAs layer growth condition range and the high-temperature buffer are consistent when growing the electrode contact layer, the n-type doping atom is silicon, the doping concentration is 1-10×10 18 cm -3 The p-type doping atom is beryllium or carbon, and the doping concentration is 1-10×10 18 cm -3 .

[0130] According to the embodiment of the present application, in S300, the current limiting layer is grown on one side or both sides of the active layer 9, the current limiting layer can comprise the first current limiting layer 8 and the second current limiting layer 10, and the current limiting layer can be AlGaAs material; the Al component of the current limiting layer is higher than that of the high-Al-component AlGaAs material in the Bragg mirror, and the growth condition is consistent with that of the Bragg mirror.

[0131] The active layer 9 is grown by using the co-evaporation and migration enhancement method; the active layer 9 adopts the multi-layer quantum dot or quantum well structure, the number is 1-30, the growth temperature is 360-530℃, and the optical thickness of the active layer 9 is 1-10λ.

[0132] Based on the characteristic that the VCSEL preparation does not need the cavity surface cleavage, the GaAs-based VCSEL can be prepared by using the off-angle germanium substrate 1 or the off-angle germanium / silicon substrate 1. The advantage is that the double-atom steps can be easily obtained on the surface of the substrate 1 by annealing pretreatment, the difficulty of heteroepitaxy between the polar mismatch materials is greatly reduced without changing the device preparation process, and the generation of the reverse phase domain at the interface can be completely suppressed.

[0133] The technical solutions of the present application are described in detail below by using the preferred embodiments. It should be noted that the specific embodiments below are only used for example and do not limit the present application.

[0134] Preparation of Sample 1

[0135] Figure 2 Ge-based vertical cavity surface emitting quantum dot laser structure diagram in Sample 1 in the embodiment of the present application.

[0136] As shown in Figure 5 the present application provides a Ge-based vertical cavity surface emitting quantum dot laser with a working wavelength of 1310 nm band, and the specific preparation method is as follows:

[0137] A semi-insulating germanium substrate 1 with a (100) crystal surface and a <110> crystal direction of 6° off-angle is selected, and a GaAs buffer layer is grown by molecular beam epitaxy. After the substrate 1 is loaded into a molybdenum holder and then into a sample chamber, the sample is first transferred to a buffer chamber for pre-evacuation treatment, and the substrate 1 is raised to 490°C and kept for 2 hours, mainly to remove impurity gases adsorbed on the surface of the germanium substrate 1. After the pre-evacuation program is completed, the sample is transferred to a growth chamber for annealing treatment, and the substrate 1 is raised to 680°C and kept for 30 minutes and then rapidly cooled, mainly to obtain a double-atom step on the surface of the germanium substrate 1, thereby eliminating the anti-phase domains generated by epitaxially growing polar GaAs material on the non-polar germanium substrate 1. In addition, all the shutters in this process are in a closed state, mainly to provide an ideal surface for the next step of growing a monolayer Ga pre-layer and to prevent interdiffusion of group V elements and the substrate 1; after the sample is cooled to 315°C and kept for 10 minutes, the main purpose is to stabilize and uniform the temperature of the substrate 1.

[0138] A nucleation layer 2 is grown by migration-enhanced epitaxy, and the growth rate of this step is as slow as possible. In this case, the growth rate of GaAs selected is 0.1 μm / h, and the V / III value is 17. During the growth process, the Ga shutter is first opened for 10 seconds to obtain a Ga pre-layer of one layer atom monolayer on the germanium surface; the Ga shutter is closed for 10 seconds; the As shutter is opened for 10 seconds and closed for 10 seconds; the cycle is repeated ten times, at which time the line-shaped stripes are changed to dots from the reflection high-energy electron diffraction instrument. The main purpose of this process is to inhibit the interdiffusion of Ga, As and Ge atoms while improving the migration length of Ga and As atoms at a lower growth temperature, thereby growing nucleation points with uniform size.

[0139] The substrate 1 is heated to 420°C, and a 100 nm thick GaAs first buffer layer 3 is grown at a rate of 0.1 μm / h by co-evaporation, and the V / III value is 12, mainly to promote the self-annihilation of anti-phase domains on the germanium substrate 1. During the growth process, the point-shaped stripes are changed to line-shaped stripes from the reflection high-energy electron diffraction instrument, and the reconstruction is (2×4), indicating that the grown GaAs changes from the initial three-dimensional island structure to a planar structure, and the anti-phase domains have been self-annihilated.

[0140] Substrate 1 is heated to 600°C and a 400 nm thick GaAs second buffer layer 4 is grown at a rate of 0.7 μm / h with a V / III ratio of 17. The main purpose is to grow a high quality GaAs surface. The three-step growth process results in an atomically flat surface, a low interfacial interdiffusion, a single domain, and a high crystal quality GaAs epitaxial layer, which is a prerequisite for the realization of a vertical cavity surface emitting laser.

[0141] Substrate 1 temperature is kept constant and a 33.5 pair GaAs / Al 0.9 Ga 0.1 As first Bragg mirror 5 is grown, where the Al 0.9 Ga 0.1 As layer is grown at a rate of 0.22 μm / h with a V / III ratio of 14 to obtain a flat Al 0.9 Ga 0.1 As surface; the GaAs layer is grown with the second buffer layer 4 growth conditions; and the optical thickness of each layer of material is 0.25 λ. The DBR material grown on the three-step buffer layer has a flat surface and a similar reflectivity spectrum to the DBR grown on the GaAs substrate 1.

[0142] Substrate 1 temperature is kept constant and a 1.75 λ optical thickness first contact layer 13 is grown with n-type doping using the second buffer layer 4 growth conditions, with a silicon doping source at a source temperature of 1020°C and a doping concentration of 1.5 x 10 18 cm -3 ;

[0143] Substrate 1 temperature is kept constant and a 0.25 λ optical thickness Al 0.98 Ga 0.02 As current confinement layer is grown at a rate of 0.2 μm / h; it is usually placed at the field antinode of the optical standing wave in the VCSEL cavity in order to minimize the optical scattering loss due to the oxide layer.

[0144] Substrate 1 temperature is reduced to 490°C and a 2 λ optical thickness quantum dot active layer 9 is grown, which includes three groups of InAs / GaAs quantum dots, where each group of quantum dots is composed of three quantum dot layers, and is located at the standing wave antinode position in order to increase the optical and material interaction to obtain high optical gain. The quantum dots are 2.7 atomic monolayers thick InAs grown at a rate of 0.06 monolayers per second, where 1.9 monolayers are co-evaporated and 0.8 monolayers are separated; this is followed by the growth of 5 nm In 0.15 Ga 0.85 As and 45 nm GaAs, respectively.

[0145] Substrate 1 temperature is increased to 600°C and a 0.25 λ optical thickness Al 0.98 Ga 0.02As the current confinement layer 10, the growth rate is 0.2 μm / h;

[0146] The substrate 1 temperature remains unchanged, and the second contact layer 1212 is grown by 1.75λ, using the growth conditions of the second buffer layer 4, while p-type doping is performed, the doping source is beryllium, the source furnace temperature is 680°C, and the doping concentration is 2x10 18 cm -3

[0147] The substrate 1 temperature remains unchanged, and 24 pairs of GaAs / Al 0.9 Ga 0.1 As the second Bragg reflector 6, the growth conditions are consistent with those of the first Bragg reflector 5; the thickness of the entire device epitaxial structure is about 14.5 μm, although the lattice adaptation of AlGaAs and GaAs is small, but due to the large thickness of the device epitaxial and the repeated growth of the DBR structure, the wafer warping of the epitaxial wafer will occur; because the germanium lattice constant is between GaAs and AlAs, the stress introduced by the AlGaAs DBR is balanced, and the high mechanical strength of the germanium substrate 1 is also much higher than that of GaAs; These characteristics improve the uniformity of the germanium-based VCSEL epitaxial wafer, and the wafer warping is also much lower than that of the epitaxial wafer with the same structure of the GaAs substrate 1.

[0148] The first photolithography is performed on the epitaxial material, and the second contact layer 12 is exposed by wet etching; H3PO4-H2O2-H2O solution is used to etch the second Bragg reflector 6 to the second contact layer 12 above the active layer 9; H3PO4-H2O2-H2O solution with a volume ratio of 1:1:6 is used for normal temperature etching, and the average etching speed is about 16 nm / s; Because the second Bragg reflector 6 is alternately grown by GaAs layer and Al 0.9 Ga 0.1 As layer, during the wet etching process, the periodic change of the color of the sample surface will be observed, so the number of color changes can be used to determine the logarithm and depth of the etched DBR; continue to use standard photolithography process, continue to use H3PO4-H2O2-H2O solution with a volume ratio of 1:1:6 to etch the mesa, and etch to the first contact layer 13;

[0149] Oxidation apertures are obtained by wet oxidation; under the conditions of N2 flow of 1 L / min, water temperature of 95°C, and furnace temperature of 580°C, the oxidation rate is about 1.5 μm / min, and oxidation apertures with a diameter of 6 μm are prepared; in order to improve the interface quality between the oxide and GaAs, after the wet oxidation is completed, the temperature remains unchanged, and in-situ annealing is performed for 20 min in N2 atmosphere;

[0150] Thermal deposition of silicon dioxide (SiO2) passivation film;

[0151] The second electrode 11 and the light outlet on the upper mesa and the first electrode 7 on the lower mesa are made of TiPtAu and AuGeNiAu respectively by thermal evaporation through multiple standard photolithography processes, and in order to form a good ohmic contact between the sample and the electrode, rapid annealing at 400℃ for 100s is performed in N2 atmosphere.

[0152] Sample 2:

[0153] Figure 3 The structure diagram of the Ge / Si-based vertical cavity surface emitting quantum well laser in sample 2 in the embodiment of the present application is shown.

[0154] As shown in Figure 3 Sample 2 provides a Ge / Si-based vertical cavity surface emitting quantum well laser with a working wavelength of 980nm. The structure adopts an external contact electrode, which reduces the difficulty of making the electrode compared with an internal contact electrode. Due to the defects at the Ge / GaAs interface, the lower electrode layer placed on the back of the substrate 1 will deteriorate the performance of the laser, and the lower electrode in the external electrode of the present patent is placed between the first buffer layer 3 and the first Bragg reflector 5. The Bragg reflector is inside the electrode, so the DBR needs to be modulated and doped and the interface composition needs to be gradually changed to reduce the resistance and free carrier absorption loss. The growth of Ge / Si-based 980nm vertical cavity surface emitting quantum well laser material and device fabrication are as follows:

[0155] A nucleation layer 2, a first buffer layer 3, a second buffer layer 4, a first Bragg reflector 5, a second Bragg reflector 6, an active layer 9, a first current limiting layer 8, a second current limiting layer 10, a first contact layer 13 and a second contact layer 12 are sequentially grown on the semi-insulating Ge / Si substrate 1 by metal organic chemical vapor deposition method;

[0156] The upper and lower mesas are obtained by standard lithography and dry etching through inductively coupled reactive ion etching, and the etching gas is selected as Cl2 and BCl3, and the etching rate is 4.5nm / s. During the etching process, the etching process is precisely controlled in situ by monitoring the reflection intensity of the He laser;

[0157] An oxidation limiting layer is formed by wet oxidation;

[0158] A passivation layer is prepared by benzocyclobutene (BCB) planarization technology, which aims to reduce the parasitic capacitance formed by the overlap of the p-type pad contact metal and the n-type bottom contact layer;

[0159] The second electrode 11 is prepared by electron beam evaporation and peeling process;

[0160] The first electrode 7 is prepared by thermal deposition method, and annealing alloying is performed;

[0161] The light outlet is prepared.

[0162] Sample 3:

[0163] Figure 4 is a structure diagram of a germanium-based vertical cavity surface emitting quantum well laser in sample 3 in the embodiment of the present application.

[0164] As shown in Figure 3 , sample 3 provides a germanium-based vertical cavity surface emitting quantum well laser with a center wavelength in the 850 nm band. The structure adopts an "outer-inner" contact electrode, which, compared with the contact mode of the previous two electrodes, reduces the difficulty of manufacturing the electrode while avoiding the problem of p-type DBR free carrier absorption. The material growth and device fabrication of the germanium-based 850 nm vertical cavity surface emitting quantum well laser are as follows:

[0165] A nucleation layer 2, a first buffer layer 3, a second buffer layer 4, a lower Bragg reflector, an active layer 9, a first current limiting layer 8, a second current limiting layer 10, a first contact layer 13 and a second contact layer 12 are sequentially grown on the n-type germanium substrate 1 by molecular beam epitaxy;

[0166] The upper and lower mesas are obtained by standard lithography and wet etching,

[0167] The first current limiting layer 8 and the second current limiting layer 10 are obtained by wet oxidation;

[0168] A silicon nitride (Si3N4) passivation layer is deposited by plasma-enhanced chemical vapor deposition technology;

[0169] The electrode port and the light output port are prepared by standard lithography, and the second electrode 11 and the first electrode 7 are prepared by sputtering process.

[0170] Sample 4

[0171] Figure 5 is a structure diagram of a germanium-based vertical cavity surface emitting quantum well laser in sample 4 in the embodiment of the present application.

[0172] As shown in Figure 5 , sample 4 provides a germanium-based vertical cavity surface emitting quantum well laser with a center wavelength in the 795 nm band. The structure adopts a non-coplanar electrode, which is a commonly used electrode structure for commercial GaAs-based lasers. The material growth and device fabrication of the germanium-based 795 nm vertical cavity surface emitting quantum well laser are as follows:

[0173] A nucleation layer 2, a first buffer layer 3, a second buffer layer 4, a lower Bragg reflector, an active layer 9, a first current limiting layer 8, a second current limiting layer 10, a second contact layer 12 are sequentially grown on the n-type germanium substrate 1 by molecular beam epitaxy;

[0174] The current limiting layer is etched by standard lithography and wet etching to obtain the mesa;

[0175] The wet oxidation obtains the current limiting layer;

[0176] The electrode port and the light outlet are prepared by standard photolithography, and the electrode second electrode 11 is prepared by sputtering method process.

[0177] The germanium substrate 1 is thinned and polished, the first electrode 7 is prepared by evaporation method, and then alloying treatment is performed to complete device production.

[0178] Sample 5:

[0179] Figure 6 It is a structure diagram of a germanium-based vertical cavity surface emitting quantum well laser in sample 5 in the embodiment of the present application.

[0180] As shown in the figure, Figure 5 Sample 5 provides a germanium-based vertical cavity surface emitting quantum well laser with a central wavelength in the 1550 nm band. The material growth and device production of the germanium-based 1550 nm vertical cavity surface emitting quantum well laser are as follows:

[0181] The nucleation layer 2, the first buffer layer 3, the second buffer layer 4, the lower Bragg reflector, the active layer 9, the first current limiting layer 8, the second current limiting layer 10, and the second contact layer 12 are sequentially grown on the germanium substrate 1 by molecular beam epitaxy.

[0182] The upper and lower mesas are obtained by standard photolithography and wet etching.

[0183] The first current limiting layer 8 and the second current limiting layer 10 are obtained by wet oxidation.

[0184] The electrode port and the light outlet are prepared by standard photolithography, and the electrode second electrode 11 is prepared by sputtering method process.

[0185] The germanium substrate 1 is thinned and polished, the first electrode 7 is prepared by evaporation method, and then alloying treatment is performed to complete device production.

[0186] Sample 6:

[0187] Figure 7 It is a structure diagram of a germanium-based vertical cavity surface emitting quantum well laser in sample 6 in the embodiment of the present application.

[0188] As shown in the figure, Figure 7 Sample 6 of the present application provides a germanium-based vertical cavity surface emitting quantum well laser with a central wavelength in the 1310 nm band. The material growth and device production of the germanium-based 1310 nm vertical cavity surface emitting quantum well laser are as follows:

[0189] The nucleation layer 2, the first buffer layer 3, the second buffer layer 4, the lower Bragg reflector, the active layer 9, the first current limiting layer 8, the second current limiting layer 10, and the first contact layer 13 are sequentially grown on the p-type germanium substrate 1 by molecular beam epitaxy.

[0190] The upper and lower platforms are obtained by standard photolithography and wet etching,

[0191] The first current limiting layer 8 and the second current limiting layer 10 are obtained by wet oxidation.

[0192] The electrode port and the light outlet are prepared by standard photolithography, and the first electrode 7 and the second electrode 11 are prepared by sputtering process.

[0193] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A vertical-cavity surface-emitting laser, comprising: The substrate is a germanium substrate or a germanium / silicon substrate; A buffer structure, covering the surface of the substrate, includes: A nucleation layer, in contact with the surface of the substrate, is used to provide nucleation sites on the surface of the substrate; A first buffer layer, covering the nucleation layer, is used to merge the three-dimensional island structure of the nucleation layer and form a surface without antiphase domains; A second buffer layer, covering the first buffer layer, is used to provide a smooth surface; A resonant cavity, disposed on the buffer structure, includes: A first Bragg reflector, located on the second buffer layer, is used to reflect light from the laser to form laser oscillations. The second Bragg reflector, separated from the first Bragg reflector by an active layer, is used to reflect light from the laser to form laser oscillations. The active layer, a quantum dot material composed of III-V group compounds, is used to provide gain for laser generation; Electrodes, disposed within the resonant cavity, are used for current injection.

2. The vertical-cavity surface-emitting laser according to claim 1, wherein, The substrate is doped in one of the following ways: semi-insulating, n-type doped, or p-type doped. The substrate may be angled or non-angled.

3. The vertical-cavity surface-emitting laser according to claim 1, wherein, The nucleation layer and the first buffer layer are III-V group compounds that are close to the lattice constant of germanium; The second buffer layer is made of GaAs material.

4. The vertical-cavity surface-emitting laser according to claim 1, wherein, It also includes an electrode contact layer. When the electrode is disposed in the resonant cavity, the electrode is disposed in the electrode contact layer. The electrode contact layer is in contact with the first Bragg reflector or the second Bragg reflector to form an ohmic contact with the electrode.

5. The vertical-cavity surface-emitting laser according to claim 1, wherein, The resonant cavity also includes a current limiting layer disposed on one or both sides of the active layer to form a current limiting aperture and limit the current injected into the active layer; The size of the current-limiting aperture is 1 to 20 micrometers.

6. The vertical-cavity surface-emitting laser according to claim 1, wherein, The emission wavelength of the quantum dot active layer is 700-1550 nm; The number of quantum dot layers is 1 to 30; The optical thickness of the active layer is 1 to 10 times λ, where λ is the center wavelength of the laser.

7. The vertical-cavity surface-emitting laser according to claim 1, wherein, Both the first and second Bragg reflectors are composed of alternating AlGaAs with two different compositions, with each layer having an optical thickness of 0.25λ. The first Bragg reflector and the second Bragg reflector are semi-insulating Bragg reflectors or doped Bragg reflectors; The doping type of the doped Bragg mirror is modulation doping or a combination of modulation doping and delta doping. The p-type doping source is beryllium or carbon, and the n-type doping source is silicon. The thickness of the composition-gradient doping is 0~30nm.

8. A method for manufacturing a vertical-cavity surface-emitting laser according to any one of claims 1-7, comprising: Growing buffer structures on a substrate; A first Bragg mirror is grown on the buffer structure; A quantum dot active layer was grown on the first Bragg mirror via co-evaporation and migration enhancement. A second Bragg mirror is grown on the active layer; Etching is performed on the laser; Electrodes are fabricated on the substrate or the electrode contact layer of the first Bragg reflector, and on the electrode contact layer of the second Bragg reflector.

9. The method according to claim 8, wherein, Also includes: A current-limiting layer is grown on the first Bragg reflector and / or the active layer; Oxidized pores are obtained on the current-limiting layer by wet oxidation.

10. The method according to claim 8, wherein, The method for growing the buffer structure includes: Pre-treat the substrate; Nucleation layer growth; Growth of the first buffer layer; A second buffer layer is grown.

Images