Detailed Description
In practicing the present invention, it was discovered that In an InGaN/GaN quantum well laser structure having a stepped upper waveguide, the upper waveguide layer of the structure utilizes InxGa1-xN layer and InyGa1-yThe N layer replaces a common upper waveguide layer, so that the injection efficiency of a hole can be improved, the optical loss can be reduced, and the slope efficiency and the power conversion efficiency of the laser can be improved.
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
According to an embodiment of the present invention, there is provided an InGaN/GaN quantum well laser having a stepped upper waveguide, including: a lower waveguide layer; a multi-quantum well layer formed on the lower waveguide layer; and a stepped upper waveguide layer formed on the MQW layer;
wherein the stepped upper waveguide layer comprises: inxGa1-xN layer and InyGa1-yN layers; inxGa1-xN layer formed on the MQW layer, InyGa1-yAn N layer is formed on the InxGa1-xN layers; x and y respectively satisfy: x is more than or equal to 0.01 and less than or equal to 0.1, y is more than or equal to 0 and less than or equal to 0.015, and x is not equal to y.
The InGaN/GaN quantum well laser adopts the stepped upper waveguide layer to regulate and control the energy band, effectively reduces the obstruction of the electron barrier layer to hole transmission, improves the hole current density injected into the multiple quantum well layer, and improves the hole injection efficiency. In addition, the stepped upper waveguide layer is favorable for guiding the light field to approach to the InGaN/GaN quantum well, the light field distributed at the high-absorption P-type layer is reduced, and the optical loss is reduced, so that the threshold current and the slope efficiency are improved, and the InGaN/GaN quantum well laser with high photoelectric performance is obtained.
According to the embodiment of the invention, the total thickness of the stepped upper waveguide layer is 70-200 nm InxGa1-xThe thickness of the N layer is 20-80 nm, InyGa1-yThe thickness of N layer is 50-120 nm for guidingThe light field is close to the quantum well layer, the light field distributed at the high-absorption P-type layer is reduced, and the optical loss is reduced, so that the InGaN/GaN quantum well violet laser with high photoelectric property is obtained.
According to an embodiment of the present invention, the InGaN/GaN quantum well laser having a stepped upper waveguide further includes: a substrate; the buffer layer is formed on one surface of the substrate; a first confinement layer formed on the buffer layer and located between the buffer layer and the lower waveguide layer; an electron blocking layer formed on the stepped upper waveguide layer; a second confinement layer formed on the electron blocking layer; an ohmic contact layer formed on the second confinement layer; a first electrode (N-type electrode) formed on the other surface of the substrate far from the buffer layer; and a second electrode (P-type electrode) formed on the ohmic contact layer.
According to an embodiment of the present invention, the substrate is a GaN substrate or a sapphire substrate; the thickness of the substrate is 50-170 μm.
According to the embodiment of the invention, the buffer layer is a GaN layer, an InGaN layer or an AlGaN layer, the buffer layer is doped in an N type, the doping element is Si, and the doping concentration is 5 multiplied by 1017cm-3~9×1018cm-3(ii) a The thickness of the buffer layer is 0.5-2.5 μm.
According to an embodiment of the present invention, the first confinement layer is N-doped AlaGa1-aN layer, a is more than or equal to 0 and less than or equal to 0.15, doping element is Si, and doping concentration is 5 multiplied by 1017cm-3~8×1018cm-3(ii) a The thickness of the first confinement layer is 0.3 to 3 μm.
According to an embodiment of the present invention, the lower waveguide layer is InhGa1-hN layer or GaN layer, h is more than or equal to 0 and less than or equal to 0.02, InhGa1-hThe N layer or the GaN layer is doped or undoped in an N type, and when the lower waveguide layer is doped in an N type, the doped element is Si; the thickness of the lower waveguide layer is 50-150 nm.
According to an embodiment of the present invention, the multiple quantum well layer includes quantum well layers and quantum barrier layers alternately arranged.
According to an embodiment of the present invention, the quantum well layer is InbGa1-bN layer, b is more than or equal to 0.03 and less than or equal to 0.3, the number of quantum well layers is 2-5, and the quantum well layersThe thickness of the single layer is 1.5-7 nm; the quantum barrier layers are GaN layers, the number of the quantum barrier layers is 3-6, the thickness of a single layer of the quantum barrier layers is 10-15 nm, and the number of the quantum well layers is one less than that of the quantum barrier layers.
According to an embodiment of the present invention, the electron blocking layer is AlcGa1-cN layer or AldIn1-dC is more than or equal to 0.1 and less than or equal to 0.3, d is more than or equal to 0.75 and less than or equal to 0.95, the electron blocking layer is doped in a P type, the doping element is Mg, and the doping concentration is 1 multiplied by 1019cm-3~7×1020cm-3(ii) a The thickness of the electron blocking layer is 10-30 nm.
According to an embodiment of the invention, the second confinement layer is AleGa1-eN layer, e is more than or equal to 0.03 and less than or equal to 0.09, the second limiting layer is doped in P type, the doping element is Mg, and the doping concentration is 3 multiplied by 1018cm-3~8×1019cm-3The thickness of the second limiting layer is 0.3 to 3 μm.
According to the embodiment of the invention, the ohmic contact layer is a GaN layer, the ohmic contact layer is doped in a P type, the doping element is Mg, and the doping concentration is 2 multiplied by 1019cm-3~3×1020cm-3(ii) a The thickness of the ohmic contact layer is 0.07-0.25 μm.
According to an embodiment of the present invention, there is also provided a method for manufacturing the InGaN/GaN quantum well laser having the stepped upper waveguide, including the following steps: manufacturing a lower waveguide layer; manufacturing a multi-quantum well layer on the lower waveguide layer; manufacturing a stepped upper waveguide layer on the multi-quantum well layer; wherein, the step-shaped upper waveguide layer manufactured on the multiple quantum well layer comprises: in formation on MQW layerxGa1-xN layers; inxGa1-xIn is formed on the N layeryGa1-yN layers, x and y respectively satisfy: x is more than or equal to 0.01 and less than or equal to 0.1, y is more than or equal to 0 and less than or equal to 0.015, and x is not equal to y.
According to the embodiment of the invention, the growth temperature of the upper waveguide layer is 700-1100 ℃.
According to an embodiment of the present invention, the above preparation method further includes: manufacturing a buffer layer on one surface of a substrate; manufacturing a first limiting layer on the buffer layer; manufacturing a lower waveguide layer on the first limiting layer; manufacturing an electron blocking layer on the stepped upper waveguide layer; manufacturing a second limiting layer on the electron blocking layer; manufacturing an ohmic contact layer on the second limiting layer; manufacturing a first electrode on the other surface of the substrate far away from the buffer layer; and manufacturing a second electrode on the ohmic contact layer.
According to an embodiment of the present invention, there is also specifically provided a method for manufacturing an InGaN/GaN quantum well laser, including the steps of:
step 1: reducing the substrate in a hydrogen atmosphere to clean the surface thereof;
step 2: with trimethyl gallium, trimethyl indium, trimethyl aluminium and ammonia (NH)3) Respectively providing Ga, In, Al and N sources for a precursor, and growing an N-type GaN, InGaN or AlGaN buffer layer on a substrate;
and step 3: h on the N-type buffer layer2As a carrier gas, growing an N-type A1GaN lower confinement layer (first confinement layer) at a high temperature;
and 4, step 4: h on the N-type AlGaN lower confinement layer2Or N2As carrier gas, epitaxially growing a GaN or InGaN lower waveguide layer;
and 5: growing InGaN/GaN multi-quantum well layer on the GaN or InGaN lower waveguide layer at the same temperature, wherein the growth temperature is 700-900 ℃, the quantum well layer is an InGaN layer, and N is used as2As a carrier gas; the quantum barrier layer is a GaN layer and is H2As a carrier gas;
step 6: epitaxially growing a step-shaped upper waveguide layer on the InGaN/GaN multi-quantum well layer at the growth temperature of 700-1100 ℃, and specifically comprising growing In on the InGaN/GaN quantum well layerxGa1-xAn N upper waveguide layer with a thickness of 20-80 nm; inxGa1-xGrowing In on the N upper waveguide layeryGa1-yN upper waveguide layer, thickness is 50 ~ 120nm, and x, y satisfy respectively: x is more than or equal to 0.01 and less than or equal to 0.1, y is more than or equal to 0 and less than or equal to 0.015, and x is not equal to y;
and 7: growing an A1GaN or AlInN electron blocking layer on the step-shaped waveguide layer at a high temperature by taking N2 as a carrier gas;
and 8: h on AlGaN or AIInN electron blocking layer2As a carrier gas, a P-type AlGaN upper confinement layer (second) is grown at high temperatureA confinement layer);
and step 9: h on the P-type AlGaN upper confinement layer2As carrier gas, growing a P-type GaN ohmic contact layer at high temperature;
step 10: evaporating an N-type electrode on the lower surface of the substrate by adopting a magnetron sputtering technology;
step 11: and (4) evaporating a P-type electrode on the upper surface of the P-type GaN ohmic contact layer by adopting a magnetron sputtering technology.
The technical solution of the present invention will be described in detail below with reference to specific examples. It should be noted that the following specific examples are only for illustration and are not intended to limit the invention.
Example 1
As shown in fig. 1, the InGaN/GaN quantum well laser with stepped upper waveguide grown by Metal Organic Chemical Vapor Deposition (MOCVD) includes: the semiconductor device comprises an N-type electrode 1, a substrate 2, an N-type buffer layer 3, an N-type lower limiting layer (first limiting layer) 4, a lower waveguide layer 5, a multi-quantum well layer 6, a stepped upper waveguide layer 7 (which is not intentionally doped), a P-type electron blocking layer 8, a P-type upper limiting layer (second limiting layer) 9, a P-type ohmic contact layer 10 and a P-type electrode 11.
The preparation method of the InGaN/GaN quantum well laser with the stepped upper waveguide comprises the following steps:
the N-type electrode 1 is Ti/Al/Ti/Au;
the substrate 2 is a GaN substrate with a thickness of 50 μm, and reduction treatment is performed on the substrate in a hydrogen atmosphere to clean the surface of the substrate; taking trimethyl gallium, trimethyl indium, trimethyl aluminum and ammonia (NH3) as precursors, respectively providing Ga, In, Al and N sources, growing an N-type buffer layer 3 on a substrate 2 at the growth temperature of 980 ℃, wherein the N-type buffer layer 3 is a GaN layer with the thickness of 2 mu m and the doping concentration of Si of 6 multiplied by 1017cm-3;
H on the N-type buffer layer 32As a carrier gas, an N-type lower limiting layer is grown at high temperature, the N-type lower limiting layer is an AlGaN layer, the thickness of the AlGaN layer is 1.5 mu m, and the doping concentration of Si is 5 multiplied by 1018cm-3The content of the Al component is 0.09;
on the N-type lower limiting layer 4 with N2As a carrier gas, the lower waveguide layer 5 is epitaxially grown,the lower waveguide layer 5 is InhGa1-hThe N layer is 100nm thick, the In component content is 0.012, and the N layer is not doped;
on the lower waveguide layer 5 with H2As a carrier gas, a multiple quantum well layer 6 was epitaxially grown at 900 deg.c, the multiple quantum well layer 6 being an InGaN/GaN layer In which two In were presentbGa1-bN quantum well sandwiched between three GaN quantum barriers, InbGa1-bThe In component of the N quantum well is 0.15, the thickness of the N quantum well is 4.5nm, the number of well layers is 2, the thickness of the GaN quantum barrier is 13nm, and the number of well layers is 3;
growing an unintentionally doped step-shaped upper waveguide layer 7 on the multiple quantum well layer 6 at the growth temperature of 700-1100 ℃, wherein In close to the quantum wellxGa1-xThe In component In the N layer was 0.025, the thickness was 60nm, InyGa1-yThe In component In the N layer is 0.005, and the thickness is 110 nm;
on the stepped upper waveguide layer 7 with H2As a carrier, growing a P-type electron blocking layer 8 at 1000 ℃, wherein the P-type electron blocking layer 8 is an AlGaN electron blocking layer, and the doping concentration of Mg is 7 multiplied by 1020cm-3The thickness is 15 nm;
h on the P-type electron blocking layer 82As a carrier, a P type upper confinement layer 9 (second confinement layer) was grown at 1200 deg.C, the P type upper confinement layer 9 being an AlGaN upper confinement layer having a thickness of 0.55 μm, an Al composition of 0.07, and a Mg doping concentration of 3X 1018cm-3;
H on the P-type upper confinement layer 92As a carrier, a P-type ohmic contact layer 10 was grown at 1100 deg.c, the P-type ohmic contact layer 10 was a GaN ohmic contact layer with a thickness of 0.12 μm and a Mg doping concentration of 3 × 1020cm-3;
And (3) evaporating a P-type electrode 11 on the P-type ohmic contact layer 10 by adopting a magnetron sputtering technology, wherein the P-type electrode is made of Pd/Pt/Au materials, and the manufacturing of the InGaN/GaN quantum well laser is completed.
Fig. 2 is a schematic structural view of the stepped upper waveguide layer 7. The step-shaped upper waveguide layer contains In along the epitaxial growth directionxGa1-xN layer 7a, InyGa1-yAnd an N layer 7 b. In which the In composition of the InGaN layer 7a was 0.025 and the thickness was 60 nm. InyGa1-yThe In composition of the N layer was 0.005 and the thickness was 110 nm.
Fig. 3 is a graph showing the relationship between the power and current of the InGaN/GaN quantum well laser having the stepped upper waveguide and the laser having the conventional upper waveguide in this embodiment. As can be seen from fig. 3, the laser with the stepped upper waveguide has a lower threshold current and higher output power than the laser with the conventional upper waveguide (i.e., single-component InGaN upper waveguide), and the slope efficiency is significantly greater than that of the violet laser with the conventional upper waveguide.
It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, mentioned in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure. The shapes and dimensions of the components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of embodiments of the present disclosure. Furthermore, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.
Furthermore, the word "comprising" does not exclude the presence of materials or steps having the same or similar functions, which are not listed in a claim. The word "a" or "an" preceding a structural element does not exclude the presence of multiple layers of structural elements having the same or similar function.
It should also be noted that unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be varied or rearranged as desired. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
The above-described embodiments of the present disclosure are not intended to limit the scope of the present disclosure. Any other corresponding changes and modifications made according to the technical idea of the present disclosure should be included in the protection scope of the claims of the present disclosure.