Edge-emitting single-mode laser provided with oxidized aperture grating and preparation method therefor

Abstract

An edge-emitting single-mode laser provided with an oxidized aperture grating (211) and a preparation method therefor. The structure of the edge-emitting single-mode laser provided with an oxidized aperture grating (211) comprises, from top to bottom, 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). A waveguide mode of the edge-emitting single-mode laser provided with an oxidized aperture grating (211) is confined by the first oxide layer (114) and the second oxide layer (131) forming a single-mode light-emitting aperture (311). The oxidized aperture grating (211) is transmitted inwards by an external etched grating, thereby spontaneously forming periodic refractive index modulation. The formed oxidized aperture grating (211) is not sensitive to etching depth, and grating position does not change along with etching depth, thereby facilitating acquisition of a repeatable and stable grating coupling coefficient. The oxidized aperture grating (211) confines a current injection window, so that device current injection efficiency is high and leakage current is small, thereby improving the performance of the edge-emitting single-mode laser.

Description

An edge-emitting single-mode laser with an oxidized aperture grating and a method for preparing the same Technical Field

[0001] The present invention relates to the field of semiconductor technology, in particular to an edge-emitting single-mode laser of an oxidized aperture grating and a preparation method thereof. Background Art

[0002] In traditional industrial mass-produced single-mode lasers, after preparing the top grating, secondary epitaxy is used to complete the growth of the cap layer structure and the fabrication of the waveguide. The etched grating is often very close to the active area. Secondary epitaxy on the etched surface can easily lead to interface growth defects, forming non-radiative recombination centers, thereby reducing the laser's injection efficiency. For single-mode lasers with sidewall gratings, especially GaAs, GaSb, and GaN-based epitaxial structures without an etched cutoff layer, due to the etching load effect, the grating region has a large difference in etching rate from the planar waveguide during dry etching. This results in a large difference in etching depth between the grating region and the planar waveguide, leading to etching footing, and making it impossible to accurately control the ideal grating coupling coefficient. If deep etching is used, although a certain grating morphology can be obtained, the surface states in the exposed active area will form a large number of non-radiative recombination centers. For small devices with narrow ridge widths, surface recombination can be quite serious, degrading the device's threshold current performance.

[0003] Furthermore, the coupling strength of sidewall gratings is relatively weak. To achieve more stable single-mode performance, a first-order grating (feature size ~100nm) is typically used to provide sufficient feedback, but this also places higher demands on exposure accuracy and etching depth. For rectangular gratings, the grating coupling coefficient can be approximately considered inversely proportional to the grating order. If a third-order grating (feature size ~300nm) is used, the grating coupling coefficient drops to one-third of that of a first-order grating, failing to provide sufficient coupling strength and resulting in unstable single-mode output.

[0004] The prior art discloses a low-refractive-index medium-supported high-contrast grating surface-emitting laser, which is manufactured using epitaxial growth technology and semiconductor planar micro-nano processing technology. A high-contrast grating is processed and manufactured on a high-contrast grating layer to form a low-refractive-index-supported high-contrast grating surface-emitting laser structure. The high-contrast grating has a higher reflectivity and a wider reflection bandwidth than the upper DBR structure, and can provide sufficient reflectivity for laser lasing. The high reflectivity is beneficial to reducing the resonant cavity loss and lowering the device threshold current. The wide high-reflectivity bandwidth better matches the resonant cavity mode, reduces the difficulty of device processing and preparation, and facilitates device lasing. The low-refractive-index medium-supported high-contrast grating structure consists of two layers of dielectric film and has a thickness of only a few hundred nanometers, which effectively reduces the difficulty of device epitaxy compared to the 3μm-5μm of P-type DBR. This prior art has the problem of using traditional secondary epitaxy to prepare buried gratings, resulting in a large number of surface defect states after etching, forming a large number of non-radiative recombination centers, and reducing the laser injection efficiency.

[0005] Summary of the Invention

[0006] One of the purposes of the present invention is to provide an edge-emitting single-mode laser with an oxidized aperture grating; a second purpose is to provide a method for preparing an edge-emitting single-mode laser with an oxidized aperture grating, so as to achieve high device current injection efficiency and low leakage current, thereby improving the performance of the edge-emitting single-mode laser.

[0007] To achieve the above objectives, the present invention provides an edge-emitting single-mode laser with an oxidized aperture grating. The structure of the edge-emitting single-mode laser with an oxidized aperture grating includes, from top to bottom, a top electrode layer, a first contact layer, a first confinement layer, a first oxide layer, an active layer, a second oxide layer, a second confinement layer, a second contact layer, and a bottom electrode layer. The waveguide mode of the edge-emitting single-mode laser with an oxidized aperture grating is confined by a single-mode light-emitting aperture formed by the first oxide layer and the second oxide layer. The oxidized aperture grating is transmitted inward from an externally etched grating, spontaneously forming a periodic refractive index modulation.

[0008] The present invention also provides a method for preparing an edge-emitting single-mode laser with an oxidized aperture grating, comprising the following steps:

[0009] S1. performing photolithography on a laser epitaxial substrate having an oxide layer structure, and obtaining a photoresist pattern for etching a grating after development;

[0010] S2, etching and stripping the photoresist pattern, wherein the etching depth exceeds the depth of the first contact layer, the first confinement layer, the first oxide layer, the active layer and the second oxide layer of the laser epitaxial structure in sequence, exposing the oxide layer window;

[0011] S3. Wet-oxidize the etched pattern obtained in S2 to form an oxidized aperture-limited waveguide and a Bragg grating structure with periodic oxidized apertures.

[0012] Preferably, the types of the edge-emitting single-mode laser include distributed feedback laser and distributed Bragg reflector laser.

[0013] Preferably, in step S1, the oxide layer comprises a double-layer structure, the oxide layers are grown on both sides of the active layer respectively, and the thickness of each oxide layer structure is 10 to 50 nm.

[0014] Preferably, in step S1, the photoresist pattern for etching the grating is a first-order or third-order grating, and the shapes of the grating teeth include rectangle, triangle and sawtooth.

[0015] Preferably, in step S2, the etching depth exceeds the second oxide layer.

[0016] Preferably, in step S3, the process parameters of the wet oxidation include process gas flow, pressure, concentration and sample temperature.

[0017] Preferably, in step S3, the structure of the oxidized aperture-limiting waveguide is determined by the oxidized length, and the size of the oxidized length is 1-3 um.

[0018] Preferably, 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 rectangular, triangular and sawtooth shapes.

[0019] Preferably, the wet oxidation process in step S3 is numerically simulated to obtain all quantitative parameters of the oxidized aperture grating, which are quantitatively used for analyzing and calculating the grating coupling coefficient of the single-mode laser.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention prepares a device structure that spontaneously forms a periodic oxidized aperture Bragg grating. The oxidized grating morphology is transferred to the center of a ridge waveguide through an externally etched grating. The formed oxidized grating is insensitive to the etching depth, and the grating position does not change with the etching depth, which is conducive to obtaining a repetitive and stable grating coupling coefficient. The device is suitable for laser material systems such as GaAs-based, GaSb-based and GaN-based lasers without an etched cutoff layer. The periodic oxidized aperture Bragg grating prepared by the present invention limits the current injection window, so that the device has high current injection efficiency and low leakage current. The light-emitting area of ​​the device is far away from the non-radiative recombination center deeply etched on the outside, which is conducive to improving the external quantum efficiency of the device. The periodic oxidized aperture Bragg grating prepared by the present invention has the effect of light confining the waveguide. The isotropic oxidation process makes the oxidized waveguide have lower scattering loss, which is conducive to improving the performance of edge-emitting single-mode lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 1 is a schematic flow chart of a method for preparing an edge-emitting single-mode laser with an oxidized aperture grating according to an embodiment of the present invention;

[0023] FIG2 is a schematic structural diagram of an edge-emitting single-mode laser of a double-layer oxidized aperture Bragg grating according to an embodiment of the present invention;

[0024] FIG3 is a schematic structural diagram of an edge-emitting single-mode laser of a single-layer oxidized aperture Bragg grating according to an embodiment of the present invention;

[0025] FIG4 is a schematic structural diagram of another single-layer oxidized aperture Bragg grating edge-emitting single-mode laser according to an embodiment of the present invention;

[0026] FIG5 is a schematic diagram of an oxidation grating forming process according to an embodiment of the present invention;

[0027] FIG6 is a SEM image of an etched grating and an oxidized grating according to an embodiment of the present invention;

[0028] 7 is a graph showing the variation of the oxidation grating length and duty cycle with oxidation depth obtained by numerical simulation according to an embodiment of the present invention;

[0029] 8 is a schematic diagram of the information flow of a method for manufacturing an edge-emitting single-mode laser with an oxidized aperture waveguide according to an embodiment of the present invention;

[0030] FIG9 is a schematic diagram of the structure of a common single-mode laser.

[0031] In the figure, 111 is the top electrode layer; 112 is the first contact layer; 113 is the first confinement layer; 114 is the first oxide layer; 121 is the active layer; 131 is the second oxide layer; 132 is the second confinement layer; 133 is the second contact layer; 134 is the bottom electrode layer; 211 is the oxidized aperture grating; and 311 is the light-emitting aperture. DETAILED DESCRIPTION

[0032] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present 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.

[0034] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0035] Furthermore, in the description of the present invention, unless otherwise specified, “plurality” means two or more.

[0036] Example 1

[0037] As shown in FIG2 , an edge-emitting single-mode laser with an oxidized aperture grating according to a preferred embodiment of the present invention comprises, from top to bottom, 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 the oxidized aperture grating is confined by a single-mode light-emitting aperture 311 formed by the first oxide layer 114 and the second oxide layer 131. The oxidized aperture grating 211 is transmitted inward from the external etched grating, spontaneously forming a periodic refractive index modulation.

[0038] Example 2

[0039] As shown in FIG1 , FIG8 , and FIG9 , a method for preparing an edge-emitting single-mode laser with an oxidized aperture grating includes the following steps:

[0040] S1. performing photolithography on a laser epitaxial substrate having an oxide layer structure, and obtaining a photoresist pattern for etching a grating after development;

[0041] S2, etching and stripping the photoresist pattern, wherein the etching depth exceeds the depth 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, exposing the oxide layer window, but precise cutoff is not required;

[0042] S3. The etched pattern obtained in S2 is wet oxidized. Due to the isotropic oxidation rate, the morphology of the etched grating is transferred inward, and the composition of the oxidized structural material changes, with a certain refractive index difference, thereby spontaneously forming an oxidized aperture-limited waveguide and a Bragg grating structure with a periodic oxidized aperture.

[0043] Types of edge-emitting single-mode lasers include, but are not limited to, distributed feedback lasers (DFB) and distributed Bragg reflector lasers (DBR).

[0044] A thin layer of the same high-aluminum composition is grown on each side of the active layer 121 of the laser epitaxial structure. After etching the external grating structure to expose the end face of the oxide layer, an isotropic wet oxidation process is performed to obtain a periodic oxide grating and waveguide structure that spontaneously forms inside the device. The prepared oxide aperture window can serve as both a current-limiting and optical-limiting window, eliminating surface recombination, reducing current leakage, and improving the device's current injection efficiency. At the same time, the oxide grating can provide additional coupling strength for the waveguide mode, compensating for the weak coupling strength of third-order and higher-order gratings, reducing the exposure process precision requirements while providing high-quality single-mode stable output.

[0045] Example 3

[0046] In step S1 , the oxide layer includes but is not limited to a double-layer structure. The oxide layers are grown on both sides of the active layer 121 , and the thickness of each oxide layer structure is 10-50 nm.

[0047] In step S1 , the photoresist pattern for etching the grating is a first-order or third-order grating, and the shapes of the grating teeth include but are not limited to rectangle, triangle and sawtooth.

[0048] In step S2 , the etching depth exceeds the second oxide layer 131 , but does not need to be precisely cut off, which has the functions of reserving the electrode mesa and transmitting the periodic grating.

[0049] In step S3 , the process parameters of the wet oxidation include process gas flow rate, pressure, concentration, and sample temperature, etc., to control the oxidation rate of the multi-component compound with a high Al component.

[0050] In step S3, the structure of the oxidized aperture-limiting waveguide is determined by the oxidized length, which is typically 1-3 μm.

[0051] In step S3, the morphology of the Bragg grating structure with periodic oxidized apertures is determined by the etched grating in step S1, including but not limited to rectangular, triangular and sawtooth shapes.

[0052] The wet oxidation process in step S3 is numerically simulated to obtain all quantitative parameters of the oxidized aperture grating, which are quantitatively used for analyzing and calculating the grating coupling coefficient of the single-mode laser. The numerical simulation process is implemented using a code program.

[0053] Compared with traditional single-mode sidewall grating lasers, the present invention is not affected by deep etching defects, does not require precise control of etching depth, and is applicable to a variety of material systems without etched cutoff layers. In addition, it makes up for the problem of insufficient high-order grating coupling strength. The oxidized aperture simultaneously plays the role of current limitation, waveguide limitation and grating coupling, thereby improving current injection efficiency, reducing waveguide loss and providing grating feedback, and preparing high-performance oxidized aperture-limited edge-emitting single-mode devices.

[0054] As shown in Figures 3, 4, 5, 6, and 7, Figure 3 is a schematic diagram of the edge-emitting single-mode laser structure of a single-layer oxidized aperture Bragg grating according to an embodiment of the present invention; Figure 4 is a schematic diagram of the edge-emitting single-mode laser structure of another single-layer oxidized aperture Bragg grating according to an embodiment of the present invention; Figure 5 is a schematic diagram of the oxidized grating formation process according to an embodiment of the present invention, with the left side being a top view of the etched grating defined by the lithography in S1. After the wet oxidation process, the high-aluminum component layer undergoes an isotropic oxidation reaction to form an insulating low-refractive-index oxide, as shown in the shaded area in the figure. Simultaneously, a high-aluminum component layer / oxide grating structure is spontaneously formed in the longitudinal direction; Figure 6 is an SEM image of the etched grating and the oxidized grating according to an embodiment of the present invention, corresponding to the right schematic diagram in Figure 5; Figure 7 is a graph of the oxidized grating length and duty cycle as a function of oxidation depth, obtained by numerical simulation according to an embodiment of the present invention. The oxidation depth is the abscissa, which can be controlled by the wet oxidation process time. The dual y-axis curves represent the duty cycle of the oxidized grating and the protrusion length of the oxidized grating, respectively, with different curves corresponding to the results under different etched grating duty cycles.

[0055] The working process of the present invention is:

[0056] S1. performing photolithography on a laser epitaxial substrate having an oxide layer structure, and obtaining a photoresist pattern for etching a grating after development;

[0057] S2, etching and stripping the photoresist pattern, wherein the etching depth exceeds the depth 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, exposing the oxide layer window, but precise cutoff is not required;

[0058] S3. The etched pattern obtained in S2 is wet oxidized. Due to the isotropic oxidation rate, the morphology of the etched grating is transferred inward, and the composition of the oxidized structural material changes, with a certain refractive index difference, thereby spontaneously forming an oxidized aperture-limited waveguide and a Bragg grating structure with a periodic oxidized aperture.

[0059] In summary, the embodiments of the present invention provide an edge-emitting single-mode laser with an oxidized aperture grating and a method for preparing the same. The laser is insensitive to etching depth and is applicable to a variety of material systems without an etched cutoff layer. The advantages are a simple preparation process, no need for secondary epitaxy, and good repeatability. In addition, the periodic Bragg oxide grating produced by the present invention has good electrical and optical confinement for the waveguide mode: the light-emitting region is far away from the deeply etched non-radiative recombination center, which improves the external quantum efficiency of the device and provides sufficient grating feedback strength. The present invention provides important design ideas and performance improvements in the field of semiconductor lasers.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. An edge-emitting single-mode laser with an oxidized aperture grating, characterized in that, The structure of the edge-emitting single-mode laser with an oxidized aperture grating includes, from top to bottom, 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 oxidized aperture grating is limited by the single-mode light-emitting aperture (311) formed by the first oxide layer (114) and the second oxide layer (131). The oxidized aperture grating (211) is transferred inward from an externally etched grating, and periodic refractive index modulation is spontaneously formed.

2. A method for preparing an edge-emitting single-mode laser with an oxidized aperture grating, characterized in that, The steps include: S1. Perform photolithography on a laser epitaxial substrate with an oxide layer structure, and after development, obtain a photoresist pattern of an etched grating. S2. Etch and remove the photoresist pattern. The etching depth successively exceeds 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, exposing the oxide layer window. S3. Perform wet oxidation on the etched pattern obtained in S2 to form an oxidized aperture-confined waveguide and a Bragg grating structure with periodic oxidized apertures.

3. The preparation method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, characterized in that, The types of the edge-emitting single-mode lasers include distributed feedback lasers and distributed Bragg reflector lasers.

4. The manufacturing method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, characterized in that, In step S1, the oxide layer includes a double-layer structure. 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.

5. The manufacturing method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, characterized in that, In step S1, the photoresist pattern of the etched grating is a first-order or third-order grating, and the grating tooth shapes include rectangle, triangle, and sawtooth.

6. The preparation method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, wherein, In step S2, the etching depth exceeds the second oxide layer (131).

7. The preparation method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, characterized in that, In step S3, the process parameters of the wet oxidation include process gas flow rate, pressure, concentration, and sample temperature.

8. The manufacturing method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, characterized in that, In step S3, the structure of the oxidized aperture-confined waveguide is determined by the oxidation length, and the size of the oxidation length is 1 - 3 μm.

9. The manufacturing method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, wherein, In step S3, the morphology of the Bragg grating structure with periodic oxidized apertures is determined by the etched grating in step S1, and includes rectangle, triangle, and sawtooth.

10. The preparation method of an edge-emitting single-mode laser with an oxidized aperture grating according to claim 2, wherein, Perform numerical simulation on the wet oxidation process in step S3 to obtain all the quantization parameters of the oxidized aperture grating, which are quantitatively used for the analysis and calculation of the grating coupling coefficient of the single-mode laser.

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