An edge-emitting single-mode laser of an oxidized aperture grating and a preparation method thereof

Abstract

The application relates to the technical field of semiconductors, and discloses an oxidized aperture grating edge-emitting single-mode laser and a preparation method thereof. The edge-emitting single-mode laser comprises a top electrode layer, a first contact layer, a first limiting layer, a first oxidation layer, an active layer, a second oxidation layer, a second limiting layer, a second contact layer and a bottom electrode layer. The waveguide mode of the oxidized aperture grating edge-emitting single-mode laser is limited by the first oxidation layer and the second oxidation layer to form a single-mode light-emitting aperture. The oxidized aperture grating is transferred from an external etched grating inwards, spontaneously forms a periodic refractive index modulation, and the oxidized grating topography is transferred from the external etched grating to the center of the ridge waveguide. The etching depth is not sensitive. The periodic oxidized aperture Bragg grating limits the current injection window, so that the device has high current injection efficiency and small leakage current. The isotropic oxidation process makes the oxidized waveguide have lower scattering loss, which is beneficial to improving the performance of the edge-emitting single-mode laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to an edge-emitting single-mode laser with an oxidized grating and a preparation method thereof. BACKGROUND

[0002] For the single-mode laser produced by traditional industrialization batch production, the growth of the cap layer structure and the fabrication of the waveguide are completed by using the secondary epitaxy after the preparation of the top grating. The etching grating distance from the active region is often very close. The surface after etching is subjected to secondary epitaxy again, which is easy to bring the growth defects of the interface, form the non-radiative recombination center, and thus reduce the injection efficiency of the laser. For the single-mode laser with the side-wall grating, especially the GaAs, GaSb, GaN-based epitaxial structure without etching stop layer, due to the etching load effect, the etching rate of the grating region is quite different from that of the planar waveguide during the dry etching process, which leads to a large difference between the etching depth of the grating region and the etching depth of the planar waveguide, resulting in the etching footing phenomenon and the inability to accurately control the ideal grating coupling coefficient. If deep etching is used, although the determined grating morphology can be obtained, the surface state of the exposed active region will form a large number of non-radiative recombination centers. For the small device with a narrow ridge width, the surface recombination can be quite serious, which deteriorates the threshold current performance of the device.

[0003] In addition, the coupling strength of the side-wall grating is relatively weak. In order to obtain more stable single-mode performance, a first-order grating (feature size ~ 100 nm) is usually used to provide sufficient feedback, but higher requirements are also put forward for the exposure accuracy and the etching depth. For the rectangular grating, the grating coupling coefficient can be approximately regarded as inversely proportional to the grating order. If a third-order grating (feature size ~ 300 nm) is used, the grating coupling coefficient will be reduced to one-third of the first-order grating, which cannot provide sufficient coupling strength, leading to unstable single-mode output of the device.

[0004] The prior art discloses a low-refractive-index medium support type high-contrast grating surface emitting laser, which is manufactured by using epitaxial growth technology and semiconductor plane micro-nano processing technology, and a high-contrast grating is processed on a high-contrast grating layer to form a low-refractive-index support type high-contrast grating surface emitting laser structure. The high-contrast grating has higher reflectivity and wider reflection bandwidth than the upper DBR structure, and can provide sufficient reflectivity for laser emission. High reflectivity is beneficial to reducing resonant cavity loss and lowering device threshold current. The low-refractive-index medium support type high-contrast grating structure is composed of two medium films and has a thickness of only several hundred nanometers, which effectively reduces epitaxial difficulty of the device compared with 3-5 mu m of the P-type DBR. The prior art has the problem of using a traditional secondary epitaxy to prepare a buried grating, and there are many surface defect states after etching, which form a large number of non-radiative recombination centers and reduce laser injection efficiency. SUMMARY

[0005] One of the purposes of the present application is to provide an oxidation aperture grating edge-emitting single-mode laser; the second purpose is to provide a preparation method of the oxidation aperture grating edge-emitting single-mode laser, so as to realize high current injection efficiency, small leakage current and improve the performance of the edge-emitting single-mode laser.

[0006] In order to achieve the above purpose, the present application provides an oxidation aperture grating edge-emitting single-mode laser, which comprises, from top to bottom, a top electrode layer, a first contact layer, a first limiting layer, a first oxidation layer, an active layer, a second oxidation layer, a second limiting layer, a second contact layer and a bottom electrode layer. The waveguide mode of the oxidation aperture grating edge-emitting single-mode laser is limited by the first oxidation layer and the second oxidation layer to form a single-mode light emitting aperture. The oxidation aperture grating is formed by inward transmission of an external etched grating and self-formation of a periodic refractive index modulation.

[0007] The present application also provides a preparation method of the oxidation aperture grating edge-emitting single-mode laser, which comprises the following steps:

[0008] S1. Photoetching is performed on a laser epitaxial substrate with an oxidation layer structure, and a photoresist pattern of an etched grating is obtained after development;

[0009] S2. Etching and photoresist removal are performed on the photoresist pattern, and the etching depth exceeds the depths of the first contact layer, the first limiting layer, the first oxidation layer, the active layer and the second oxidation layer of the laser epitaxial structure in sequence, and an oxidation layer window is exposed;

[0010] S3. Wet oxidation is performed on the etched pattern obtained in S2 to form an oxidation aperture limiting waveguide and a periodic oxidation aperture Bragg grating structure.

[0011] Preferably, the type of the edge-emitting single-mode laser includes a distributed feedback laser and a distributed Bragg reflection laser.

[0012] Preferably, in step S1, the oxide layer includes a double-layer structure, and the oxide layer is respectively grown on both sides of the active layer, and the thickness of each layer of the oxide layer structure is 10-50 nm.

[0013] Preferably, in step S1, the photoresist pattern of the etched grating is a first-order or third-order grating, and the grating tooth shape includes a rectangle, a triangle and a sawtooth shape.

[0014] Preferably, in step S2, the etching depth exceeds the second oxide layer.

[0015] Preferably, in step S3, the process parameters of the wet oxidation process include a process gas flow, a pressure, a concentration and a sample temperature.

[0016] Preferably, in step S3, the structure of the oxidized aperture-limited waveguide is determined by an oxidation length, and the size of the oxidation length is 1-3 um.

[0017] Preferably, in step S3, the morphology of the periodic oxidized aperture Bragg grating structure is determined by the etched grating in step S1, and includes a rectangle, a triangle and a sawtooth shape.

[0018] Preferably, the wet oxidation process in step S3 is numerically simulated to obtain all the quantitative parameters of the oxidized aperture grating, which are quantitatively used for grating coupling coefficient analysis and calculation of the single-mode laser.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] The present application prepares a device structure in which a periodic oxidized aperture Bragg grating is formed spontaneously, the oxidation grating morphology is transmitted to the center of the ridge waveguide through the external etched grating, the formed oxidation grating is not sensitive to the etching depth, the grating position does not change with the etching depth, which is beneficial to obtain a repeatedly stable grating coupling coefficient, and is suitable for GaAs-based, GaSb-based and GaN-based laser material systems without etching stop layer; the periodic oxidized aperture Bragg grating prepared by the present application limits the current injection window, so that the device has high current injection efficiency and small leakage current, and the device light-emitting region is far away from the external deep etching non-radiation recombination center, which is beneficial to improve the external quantum efficiency of the device; the periodic oxidized aperture Bragg grating prepared by the present application has the effect of light-limited waveguide, and the isotropic oxidation process makes the oxidation waveguide have lower scattering loss, which is beneficial to improve the performance of the edge-emitting single-mode laser. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a flowchart of a preparation method of an edge-emitting single-mode laser of an oxidized-aperture grating according to an embodiment of the present application;

[0022] Figure 2 is a structural diagram of an edge-emitting single-mode laser of a double-layer oxidized-aperture Bragg grating according to an embodiment of the present application;

[0023] Figure 3 is a structural diagram of an edge-emitting single-mode laser of a single-layer oxidized-aperture Bragg grating according to an embodiment of the present application;

[0024] Figure 4 is a structural diagram of an edge-emitting single-mode laser of another single-layer oxidized-aperture Bragg grating according to an embodiment of the present application;

[0025] Figure 5 is a schematic diagram of an oxidized grating forming process according to an embodiment of the present application;

[0026] Figure 6 is a SEM image of an etched grating and an oxidized grating according to an embodiment of the present application;

[0027] Figure 7 is a graph of the length and duty cycle of an oxidized grating varying with the oxidation depth according to an embodiment of the present application;

[0028] Figure 8 is a flowchart of a preparation method of an edge-emitting single-mode laser of an oxidized-aperture waveguide according to an embodiment of the present application;

[0029] Figure 9 is a structural diagram of a common single-mode laser.

[0030] In the figure, 111 is a top electrode layer; 112 is a first contact layer; 113 is a first confinement layer; 114 is a first oxidation layer; 121 is an active layer; 131 is a second oxidation layer; 132 is a second confinement layer; 133 is a second contact layer; 134 is a bottom electrode layer; 211 is an oxidized-aperture grating; and 311 is an out-coupling aperture. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application will be further described in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not used to limit the scope of the present application.

[0032] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] Example 1

[0036] like Figure 2 As shown, a preferred embodiment of the present invention provides an edge-emitting single-mode laser with an oxide aperture grating. The structure of the edge-emitting single-mode laser with an oxide aperture grating, from top to bottom, includes a top electrode layer 111, a first contact layer 112, a first confinement layer 113, a first oxide layer 114, an active layer 121, a second oxide layer 131, a second confinement layer 132, a second contact layer 133, and a bottom electrode layer 134. The waveguide mode of the edge-emitting single-mode laser with an oxide aperture grating is confined by the single-mode output aperture 311 formed by the first oxide layer 114 and the second oxide layer 131. The oxide aperture grating 211 is transmitted from the external etched grating inward, spontaneously forming periodic refractive index modulation.

[0037] Example 2

[0038] like Figure 1 , Figure 8 , Figure 9 As shown, a method for fabricating an edge-emitting single-mode laser with an oxide aperture grating includes the following steps:

[0039] S1. Photolithography is performed on a laser epitaxial substrate with an oxide layer structure, and the photoresist pattern of the etched grating is obtained after development.

[0040] S2, etching and removing the photoresist pattern, the etching depth exceeds the first contact layer 112, the first confinement layer 113, the first oxide layer 114, the active layer 121 and the second oxide layer 131 of the laser epitaxial structure in turn, and the oxide layer window is exposed, but it does not need to be accurately cut off;

[0041] S3, wet oxidation of the etching pattern obtained in S2, due to the isotropic oxidation rate, the morphology of the etching grating is transmitted inward, the composition of the oxidized structure material changes, and there is a certain refractive index difference, so that the oxidized aperture restriction waveguide and the periodic oxidized aperture Bragg grating structure are spontaneously formed.

[0042] The types of edge-emitting single-mode lasers include but are not limited to distributed feedback lasers (DFB) and distributed Bragg reflector lasers (DBR).

[0043] A thin layer of the same high aluminum component is grown on both sides of the active layer 121 of the laser epitaxial structure. After etching the external grating structure and exposing the oxide layer end face, a periodic oxidation grating and waveguide structure are spontaneously formed inside the device by performing an isotropic wet oxidation process. The prepared oxidation aperture window can simultaneously act as a current limiting and optical limiting window, eliminating surface recombination, reducing current leakage, and improving the current injection efficiency of the device. At the same time, the oxidation grating can provide additional coupling strength for the waveguide mode, making up for the weakness of the third-order and higher-order grating coupling strength, reducing the precision requirement of the exposure process, and providing high-quality single-mode stable output.

[0044] Embodiment three

[0045] In step S1, the oxide layer includes but is not limited to a double-layer structure, and the oxide layer is grown on both sides of the active layer 121. The thickness of each oxide layer structure is 10-50 nm.

[0046] In step S1, the photoresist pattern of the etching grating is a first-order or third-order grating, and the grating tooth shape includes but is not limited to a rectangle, a triangle and a sawtooth shape.

[0047] In step S2, the etching depth exceeds the second oxide layer 131, but it does not need to be accurately cut off, which has the effect of reserving the electrode mesa and transmitting the periodic grating.

[0048] In step S3, the process parameters of wet oxidation include process gas flow, pressure, concentration and sample temperature, etc., which control the oxidation rate of the multi-component compound with high Al component.

[0049] In step S3, the structure of the oxidized aperture waveguide is determined by the oxidation length, and the typical size of the oxidation length is 1-3 um.

[0050] In step S3, the morphology of the Bragg grating structure of the periodic oxidized aperture is determined by the etched grating in step S1, including but not limited to rectangle, triangle and sawtooth.

[0051] The wet oxidation process in step S3 is numerically simulated to obtain all the quantitative parameters of the oxidized aperture grating, which is quantitatively used for the grating coupling coefficient analysis and calculation of the single-mode laser. The numerical simulation process is realized by a code program.

[0052] Compared with the traditional single-mode side wall grating laser, the present application is not affected by the etching defect, does not need to accurately control the etching depth, and is suitable for a variety of material systems without etching stop layer. In addition, the problem of insufficient high-order grating coupling strength is solved, the oxidized aperture simultaneously plays the roles of current limiting, waveguide limiting and grating coupling, thereby improving the current injection efficiency, reducing the waveguide loss and providing grating feedback, and preparing a high-performance oxidized aperture limited edge-emitting single-mode device.

[0053] As shown in Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , wherein Figure 3 is a schematic diagram of an edge-emitting single-mode laser structure of a single-layer oxidized aperture Bragg grating according to an embodiment of the present application; Figure 4 is a schematic diagram of another edge-emitting single-mode laser structure of a single-layer oxidized aperture Bragg grating according to an embodiment of the present application; Figure 5 is a schematic diagram of an oxidized grating formation process according to an embodiment of the present application, the left side is a top view of the etched grating defined by photolithography in S1, after the wet oxidation process, the isotropic oxidation reaction of the high aluminum component layer occurs, forming an insulating low refractive index oxide, as shown in the shaded part in the figure, and a grating structure of the high aluminum component layer / oxide is also spontaneously formed in the longitudinal direction; Figure 6 is a SEM diagram of the etched grating and the oxidized grating according to an embodiment of the present application, corresponding to the right schematic diagram in Figure 5 ; Figure 7 is a graph of the oxidized grating length and duty cycle varying with the oxidation depth obtained by numerical simulation according to an embodiment of the present application, the oxidation depth is the abscissa, which can be controlled by the process time of the wet oxidation, the double-y-axis curves respectively represent the duty cycle of the oxidized grating and the protruding length of the oxidized grating, and different curves correspond to the results under different etched grating duty cycles.

[0054] The working process of the present application is as follows:

[0055] S1, photoetching is performed on a laser epitaxial substrate with an oxidation layer structure, and after development, a photoetching glue pattern of etching grating is obtained;

[0056] S2, etching and glue removal are performed on the photoetching glue pattern, the etching depth exceeds the depths of the first contact layer 112, the first limiting layer 113, the first oxidation layer 114, the active layer 121 and the second oxidation layer 131 of the laser epitaxial structure in turn, and an oxidation layer window is exposed, but accurate cutoff is not required;

[0057] S3, wet oxidation is performed on the etching pattern obtained in S2, due to the isotropic oxidation rate, the morphology of the etching grating is transmitted inward, the composition of the oxidized structure material is changed, and a certain refractive index difference is generated, so that an oxidation aperture grating, an oxidation aperture restriction waveguide and a periodic oxidation aperture Bragg grating structure are spontaneously formed.

[0058] In summary, the embodiment of the present application provides an edge-emitting single-mode laser with an oxidation aperture grating and a preparation method thereof, which is not sensitive to etching depth, is suitable for a variety of material systems without etching cutoff layer, and has the advantages of simple preparation process, no secondary epitaxy and good repeatability. In addition, the periodic Bragg oxidation grating manufactured by the present application has good electrical and optical restrictions on waveguide modes: the light-emitting area is far away from the non-radiative recombination center of deep etching, the external quantum efficiency of the device is improved, and sufficient grating feedback strength is provided. The present application provides an important design idea and performance improvement for the field of semiconductor lasers.

[0059] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the technical field, several improvements and replacements can be made without departing from the technical principles of the present application, and these improvements and replacements should also be considered as the protection scope of the present application.

Claims

1. An edge-emitting single-mode laser of an oxidized hole diameter grating, characterized by, The structure of the oxide-aperture grating edge-emitting single-mode laser from top to bottom comprises a top electrode layer (111), a first contact layer (112), a first confinement layer (113), a first oxide layer (114), an active layer (121), a second oxide layer (131), a second confinement layer (132), a second contact layer (133), and a bottom electrode layer (134), the waveguide mode of the oxide-aperture grating edge-emitting single-mode laser is limited by the first oxide layer (114) and the second oxide layer (131) to form a single-mode light-emitting aperture (311), and the oxide-aperture grating (211) is formed by inward transmission of an external etching grating and spontaneous formation of a periodic refractive index modulation. The preparation method of the edge-emitting single-mode laser is characterized in that the method comprises the following steps: S1, performing photoetching on a laser epitaxial substrate with an oxide layer structure, and obtaining an etching grating photoresist pattern after development; S2, etching and removing the photoresist pattern, the etching depth exceeding the depths of the first contact layer (112), the first confinement layer (113), the first oxide layer (114), the active layer (121), and the second oxide layer (131) of the laser epitaxial structure in sequence, and exposing an oxide layer window; S3, performing wet oxidation on the etching pattern obtained in S2 to form an oxide-aperture limited waveguide and a Bragg grating structure of a periodic oxide aperture; S4, performing numerical simulation on the wet oxidation process in step S3 to obtain all quantitative parameters of the oxide-aperture grating, which are used for quantitative grating coupling coefficient analysis and calculation of the single-mode laser.

2. The method of claim 1, wherein the oxidizing is performed by using a solution of hydrogen peroxide. The type of the edge-emitting single-mode laser comprises a distributed feedback laser and a distributed Bragg reflection laser.

3. The method of claim 1, wherein the oxidizing is performed by using a solution of hydrogen peroxide (H202) and sulfuric acid (H2S04) with a concentration of 30% and 98%, respectively. In step S1, the oxide layer comprises a double-layer structure, and the oxide layers are respectively grown on both sides of the active layer (121), and the thickness of each oxide layer structure is 10-50 nm.

4. The method of claim 1, wherein the method further comprises: In step S1, the photoresist pattern of the etching grating is a first-order or third-order grating, and the grating tooth shape comprises a rectangle, a triangle, and a sawtooth shape.

5. The method of claim 1, wherein the method further comprises: In step S2, the etching depth exceeds the second oxide layer (131). ​ 6. The method of claim 1, wherein the method further comprises: In step S3, the process parameters of the wet oxidation process comprise process gas flow, pressure, concentration, and sample temperature.

7. The method of claim 1, wherein the method further comprises: forming a first cladding layer on the substrate; forming a second cladding layer on the first cladding layer; and forming a third cladding layer on the second cladding layer. In step S3, the structure of the oxide-aperture limited waveguide is determined by an oxidation length, and the size of the oxidation length is 1-3 um.

8. The method of claim 1, wherein the method further comprises: In step S3, the morphology of the Bragg grating structure of the periodic oxide aperture is determined by the etching grating in step S1, and comprises a rectangle, a triangle, and a sawtooth shape.

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