GaN-based laser chip and preparation method thereof

Abstract

The invention provides a GaN-based laser chip and a preparation method thereof. The GaN-based laser chip sequentially comprises an n-type electrode (20), a substrate (10), an n-type limiting layer (12), a lower waveguide layer (13), an active layer (14), an upper waveguide layer (15), an upper limiting layer and a p-type electrode (19) from bottom to top, wherein the upper limiting layer sequentially comprises a p-type limiting layer (16), a current expansion layer (17) and an air layer from bottom to top; passivation layers (18) are arranged on the two sides of the p-type limiting layer (16), the air layer is formed in the middle of the p-type electrode (19), and the orthographic projection of the p-type electrode (19) in the XY plane does not cover the orthographic projection of the p-type limiting layer (16) in the XY plane. According to the GaN-based laser chip disclosed by the invention, the p-type limiting layer (16), the current expansion layer (17) and the air layer jointly form the upper limiting layer, so that the light field limitation of the laser is increased, the mode loss of the laser is reduced, and the series resistance of the laser is reduced.

Description

Technical Field

[0001] The present disclosure relates to the technical field of semiconductor optoelectronic devices, and in particular to a GaN-based laser chip and a preparation method thereof. Background Art

[0002] GaN-based materials are called III-group nitride materials (including InN, GaN, AlN, InGaN, AlGaN, etc., with a bandgap range of 0.7~6.2eV). The spectrum covers the near-infrared to deep ultraviolet bands. It is considered to be the third-generation semiconductor after Si and GaAs, and has important application value in the field of optoelectronics. GaN lasers are composed of n-AlGaN, quantum wells, and p-AlGaN heterojunctions, in which p-AlGaN is not only a vacancy injection layer, but also a light confinement layer. In the GaN-based laser structure, the thickness of p-AlGaN is generally above 500nm to ensure a high light field confinement factor. However, due to the difficulty in activating p-AlGaN impurities and the high resistivity of p-AlGaN, the resistance of thick p-AlGaN layers is large. At the same time, thick p-AlGaN increases the stress of the epitaxial layer, and high-temperature growth of p-AlGaN will also cause thermal degradation of the quantum well, thereby limiting the performance of GaN-based lasers. Summary of the invention

[0003] In view of this, the first aspect of the present disclosure provides a GaN-based laser chip, characterized in that it includes, from bottom to top: an n-type electrode, a substrate, an n-type confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer and a p-type electrode; wherein the upper confinement layer includes, from bottom to top: a p-type confinement layer, a current spreading layer and an air layer; a passivation layer is provided on both sides of the p-type confinement layer, an air layer is formed in the middle of the p-type electrode, and the orthographic projection of the p-type electrode in the XY plane does not cover the orthographic projection of the p-type confinement layer in the XY plane.

[0004] According to an embodiment of the present disclosure, the material of the p-type confinement layer is AlGaN, the growth temperature is 900-1200° C., and the thickness is 50-200 nm; the p-type confinement layer is etched by ICP to form a ridge region.

[0005] According to an embodiment of the present disclosure, the material of the current spreading layer is ITO or other metal material with a refractive index lower than that of the p-type confinement layer, and the thickness is 10-100 nm; the current spreading layer is formed on the p-type confinement layer by evaporation.

[0006] According to an embodiment of the present disclosure, the material of the passivation layer is silicon dioxide or silicon nitride, and the thickness is the same as that of the p-type confinement layer; the passivation layer is formed on both sides of the ridge region of the p-type confinement layer by evaporation.

[0007] According to an embodiment of the present disclosure, the position of the p-type electrode corresponds to the position of the passivation layer; the p-type electrode and the n-type electrode are formed by evaporation.

[0008] According to the embodiments of the present disclosure, the active layer is a single quantum well structure or a multi-quantum well structure composed of a quantum well layer and a quantum barrier layer, and the light emission wavelength is 300 to 600 nm; the growth temperature of the active layer is 700 to 900°C; the material of the quantum well layer is one of AlGaN, GaN, InGaN or AlInGaN, and the material of the quantum barrier layer is one of AlGaN, GaN or InGaN.

[0009] According to an embodiment of the present disclosure, the material of the substrate is one of gallium nitride, silicon carbide or silicon.

[0010] According to an embodiment of the present disclosure, the upper waveguide layer is a non-doped upper waveguide layer, and the material is one of InGaN, GaN or AlGaN; the growth temperature of the upper waveguide layer is higher than the growth temperature of the active layer.

[0011] According to an embodiment of the present disclosure, a non-doped GaN layer is further included between the substrate and the n-type confinement layer.

[0012] The second aspect of the present disclosure provides a preparation method of the GaN-based laser chip according to the above-mentioned method, comprising: S1, sequentially growing an n-type confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer and a p-type confinement layer on a substrate; S2, etching and removing the areas on both sides of the p-type confinement layer, vapor-depositing a passivation material on the surface of the etched sample, removing excess passivation material above the p-type confinement layer, and forming passivation layers on both sides; S3, vapor-depositing on the p-type confinement layer and the passivation layer to form a current spreading layer; S4, vapor-depositing a p-type electrode material, removing the p-type electrode material above the p-type confinement layer, exposing at least part of the current spreading layer to the air, and obtaining a p-type electrode; wherein the p-type confinement layer, the current spreading layer and the air layer together constitute an upper confinement layer; S5, vapor-depositing under the substrate to form an n-type electrode, and obtaining a GaN-based laser chip.

[0013] The GaN-based laser chip disclosed in the present invention utilizes a p-type confinement layer, a current expansion layer and an air layer to jointly constitute an upper confinement layer, thereby reducing the thickness of the p-type confinement layer and shortening the growth time of the p-type confinement layer, reducing the resistance of the laser, and reducing damage to the quantum well; and by introducing a low-refractive index current expansion layer and an air layer, the laser light field confinement is increased, thereby improving the output power and photoelectric conversion efficiency of the GaN-based laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0015] Figure 1 A schematic cross-sectional view of a GaN-based laser chip according to an embodiment of the present disclosure is shown;

[0016] Figure 2 The schematic diagram of the three-dimensional structure of the GaN-based laser chip according to the embodiment of the present disclosure is shown;

[0017] Figure 3 The flowchart of the method for preparing a GaN-based laser chip according to an embodiment of the present disclosure is schematically shown;

[0018] Description of Figure Numbers:

[0019] 10, substrate; 11, undoped GaN layer; 12, n-type confinement layer; 13, lower waveguide layer; 14, active layer; 15, upper waveguide layer; 16, p-type confinement layer; 17, current spreading layer; 18, passivation layer; 19, p-type electrode; 20, n-type electrode. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0021] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0022] Various directional words in the present disclosure, such as "front", "back", "left", "right", "up", "down", etc., are only for the convenience of description and are used to describe the relative position relationship between the various components, rather than to limit the present disclosure. Different product placement methods of the present disclosure may result in changes in the various directional descriptions.

[0023] The present disclosure provides a GaN-based laser chip, see Figure 1~Figure 2 , from bottom to top, it includes: an n-type electrode 20, a substrate 10, an n-type confinement layer 12, a lower waveguide layer 13, an active layer 14, an upper waveguide layer 15, an upper confinement layer and a p-type electrode 19; wherein, the upper confinement layer includes, from bottom to top, a p-type confinement layer 16, a current spreading layer 17 and an air layer; a passivation layer 18 is provided on both sides of the p-type confinement layer 16, an air layer is formed in the middle of the p-type electrode 19, and the orthographic projection of the p-type electrode 19 in the XY plane does not cover the orthographic projection of the p-type confinement layer 16 in the XY plane.

[0024] The GaN-based laser chip disclosed in the present invention has a new type of composite confinement layer, which is composed of a p-type confinement layer 16, a current expansion layer 17 and an air layer. Among them, the current expansion layer 17 has a low refractive index, but a large absorption, and the thickness of the current expansion layer 17 should not be too thick; while the air has a low refractive index and a small absorption. The new composite confinement layer can increase the laser light field confinement while reducing the laser mode loss and the series resistance of the laser. At the same time, the thickness of the p-type confinement layer 16 is thinned and the growth time is shortened, which can effectively reduce the problem of quantum well degradation caused by high-temperature baking, and improve the output power and photoelectric conversion efficiency of the GaN-based laser.

[0025] Based on the above embodiment, the material of the p-type confinement layer 16 is AlGaN, the growth temperature is 900-1200° C., and the thickness is 50-200 nm; the p-type confinement layer 16 is etched by ICP to form a ridge region.

[0026] The p-type confinement layer 16 is a part of the upper confinement layer, and acts as a hole injection layer and partially confines the light field in the laser chip. The growth temperature of the p-type confinement layer 16 within the above range is beneficial to reduce the resistivity of the p-AlGaN material and reduce the damage to the quantum well caused by high-temperature growth of p-AlGaN. The p-type confinement layer 16 is thinner than the p-type confinement layer of a conventional GaN-based laser (>500nm), and the purpose is to reduce the series resistance of the GaN-based laser by reducing the thickness of the high-resistance p-type confinement layer 16.

[0027] Based on the above embodiment, the material of the current spreading layer 17 is ITO or other metal material with a refractive index lower than that of the p-type confinement layer 16 , and the thickness is 10-100 nm; the current spreading layer 17 is formed on the p-type confinement layer 16 by evaporation.

[0028] The current spreading layer 17 is plated on the p-type confinement layer 16 by electron beam evaporation or magnetron sputtering, and acts as a part of the upper confinement layer and the current spreading layer. The current spreading layer 17 is a metal layer, and its resistivity is much lower than that of the p-type confinement layer 16. However, since the ITO layer has a large light absorption coefficient, the thickness of the ITO layer of this structure is relatively thin, generally 10-100 nm, to achieve good current spreading, increase the uniformity of the injected current, and reduce the absorption of the light field by the ITO layer, thereby reducing the mode loss of the device.

[0029] Based on the above embodiment, the material of the passivation layer 18 is silicon dioxide or silicon nitride, and the thickness is the same as that of the p-type confinement layer 16 ; the passivation layer 18 is formed on both sides of the ridge region of the p-type confinement layer 16 by evaporation.

[0030] The passivation layer 18 plays the role of passivation and supporting the current spreading layer 17. Before growing the silicon dioxide (SiO2) or silicon nitride (SiN) passivation layer 18, the p-type confinement layer 16 is first etched into a ridge region by the ICP method. The etching depth varies slightly according to the spot shape of the transverse film and the refractive index of the ridge region. The silicon dioxide (SiO2) or silicon nitride (SiN) passivation layer 18 is grown on the etched structure by the CVD method.

[0031] On the basis of the above embodiment, the position of the p-type electrode 19 corresponds to the position of the passivation layer 18; the p-type electrode 19 and the n-type electrode 20 are formed by evaporation.

[0032] The p-type electrode 19 is deposited on the current spreading layer 17 by electron beam evaporation or other methods. The characteristic of the p-type electrode 19 is that the position corresponding to the ridge region of the p-type confinement layer 16 is not covered by the p-type electrode 19, so that the air layer between the p-type electrode 19, the current spreading layer 17 and the p-type confinement layer 16 together constitute the upper confinement layer of the GaN-based laser. Since the refractive index of the current spreading layer 17 and the air layer is relatively low, a high light confinement factor can be achieved at a relatively thin thickness. At the same time, not covering the electrode above the ridge can effectively reduce the mode loss of the GaN laser caused by electrode absorption, thereby improving the laser's lasing characteristics. The injected current is injected into the current spreading layer 17 through the p-type electrode 19 to achieve current homogenization, and then injected into the active layer 14 through the etched p-type confinement layer 16 to achieve electrical injection luminescence.

[0033] On the basis of the above embodiments, the active layer 14 is a single quantum well structure or a multi-quantum well structure composed of a quantum well layer and a quantum barrier layer, and the light emission wavelength is 300nm~600nm; the growth temperature of the active layer 14 is 700~900℃; the material of the quantum well layer is one of AlGaN, GaN, InGaN or AlInGaN, and the material of the quantum barrier layer is one of AlGaN, GaN or InGaN.

[0034] The active layer 14 is a quantum well light-emitting layer structure, which is grown on the undoped lower waveguide layer 13 to achieve light-emitting effect.

[0035] Based on the above embodiments, the material of the substrate 10 is one of gallium nitride, silicon carbide or silicon.

[0036] The n-type electrode 20 is deposited on the substrate 10 by electron beam evaporation or other methods, and serves as the negative electrode of the entire GaN-based laser chip.

[0037] On the basis of the above embodiment, the upper waveguide layer 15 is a non-doped upper waveguide layer, and the material is one of InGaN, GaN or AlGaN; the growth temperature of the upper waveguide layer 15 is higher than the growth temperature of the active layer 14 .

[0038] The non-doped upper waveguide layer 15 is grown on the active layer 14. The non-doped upper waveguide layer 15 is generally made of InGaN, GaN or AlGaN material, and its growth temperature is generally higher than that of the active layer 14, for example, 750-1100°C.

[0039] On the basis of the above embodiment, a non-doped GaN layer 11 is further included between the substrate 10 and the n-type confinement layer 12 .

[0040] The non-doped GaN layer 11 is grown on the substrate 10 and serves as a template for subsequent material growth. The n-type confinement layer 12 is grown on the non-doped GaN layer 11. The material of the n-type confinement layer 12 is AlGaN, the growth temperature is 1000-1200°C, and the thickness is 0.5-1μm. The non-doped lower waveguide layer 13 is grown on the n-type confinement layer 12. The refractive index difference between the AlGaN lower confinement layer and the non-doped lower waveguide layer is used to confine the light in the waveguide layer.

[0041] The present disclosure also provides a method for preparing the GaN-based laser chip according to the above, referring to Figure 3 , including: S1, sequentially growing an n-type confinement layer 12, a lower waveguide layer 13, an active layer 14, an upper waveguide layer 15 and a p-type confinement layer 16 on a substrate 10; S2, etching and removing the areas on both sides of the p-type confinement layer 16, evaporating a passivation material on the surface of the etched sample, removing excess passivation material above the p-type confinement layer 16, and forming a passivation layer 18 on both sides; S3, evaporating on the p-type confinement layer 16 and on the passivation layer 18 to form a current spreading layer 17; S4, evaporating a p-type electrode material, removing the p-type electrode material above the p-type confinement layer 16, exposing at least part of the current spreading layer 17 to the air, and obtaining a p-type electrode 19; wherein the p-type confinement layer 16, the current spreading layer 17 and the air layer together constitute an upper confinement layer; S5, evaporating under the substrate 10 to form an n-type electrode 20, and obtaining a GaN-based laser chip.

[0042] Specifically, it includes:

[0043] (1) A non-doped GaN layer 11 is grown on a substrate 10 to serve as a template for subsequent material growth.

[0044] (2) An n-type confinement layer 12 is grown on the non-doped GaN layer 11. The material is AlGaN. The growth temperature is 1000-1200°C and the thickness is 0.5-1 μm.

[0045] (3) An undoped lower waveguide layer 13 is grown on the n-type confinement layer 12, and the light is confined in the waveguide layer by utilizing the refractive index difference between the AlGaN lower confinement layer and the undoped lower waveguide layer.

[0046] (4) An active layer 14 is grown on the undoped lower waveguide layer 13, and the light emission wavelength thereof is between 300 and 600 nm. The active layer 14 is a single quantum well structure or a multi-quantum well structure consisting of a quantum well layer and a quantum barrier layer, wherein the quantum well layer is made of AlGaN or GaN or InGaN or AlInGaN material, and the quantum barrier layer is made of AlGaN or GaN or InGaN, and the growth temperature of the quantum well region is between 700 and 900°C.

[0047] (5) A non-doped upper waveguide layer 15 is grown on the active layer 14. The non-doped upper waveguide layer 15 is generally made of InGaN, GaN or AlGaN material. Its growth temperature is generally higher than the growth temperature of the active layer 14, generally 750-1100°C.

[0048] (6) A p-type confinement layer 16 is grown on the undoped upper waveguide layer 15. The material is AlGaN. The growth temperature is 900-1200°C and the thickness is between 50 and 200 nm. This layer is part of the upper confinement layer. This layer is thinner than the thickness of the p-type confinement layer of a conventional GaN-based laser (>500 nm). The purpose is to reduce the series resistance of the GaN-based laser by reducing the thickness of the high-resistance p-type confinement layer. After this step is completed, the epitaxial process of the entire structure is completed.

[0049] (7) After the epitaxial wafer undergoes photolithography, etching and other process steps, the AlGaN material on both sides is removed and the ridge region of the laser is prepared.

[0050] (8) A silicon dioxide or silicon nitride passivation layer 18 is deposited on both sides and above the p-type confinement layer 16 by photolithography, electron beam evaporation or magnetron sputtering. The thickness of the passivation layer 18 is the same as that of the p-type confinement layer 16, and plays the role of passivation and supporting the current spreading layer 17. The silicon dioxide passivation material above the ridge region of the p-type confinement layer 16 is removed by a stripping method to obtain the passivation layer 18.

[0051] (9) The current spreading layer 17 is deposited on the p-type confinement layer 16 and the passivation layer 18 by electron beam evaporation or magnetron sputtering. The material is ITO or other metal materials with a refractive index smaller than that of the p-type confinement layer 16. The ITO current spreading layer is a metal layer, and its resistivity is much lower than that of the p-type confinement layer 16. However, since the ITO layer has a large light absorption coefficient, the thickness of the ITO layer of this structure is relatively thin, generally 10~100nm, to achieve good current spreading, increase the uniformity of the injected current, and at the same time reduce the ITO layer's absorption of the light field, thereby reducing the device's mode loss.

[0052] (10) The p-type electrode 19 is deposited on the current spreading layer 17 by photolithography, electron beam evaporation and other methods. The p-type electrode material above the ridge region is removed by a debonding method to obtain the final patterned p-type electrode 19. At this time, a portion of the current spreading layer 17 is directly exposed to the air. The air layer between the p-type electrode 19, the current spreading layer 17 and the p-type confinement layer 16 together constitute the upper confinement layer of the GaN-based laser. Since the refractive index of the current spreading layer 17 and the air layer is low, a high light confinement factor can be achieved at a relatively thin thickness. At the same time, the p-type confinement layer 16 is not covered with electrode material, which can effectively reduce the mode loss of the GaN laser caused by electrode absorption, thereby improving the laser's lasing characteristics. The injected current is injected into the current spreading layer 17 through the p-type electrode 19 to achieve current homogenization, and then injected into the active layer 14 through the etched p-type confinement layer 16 to achieve electrical injection luminescence.

[0053] (11) An n-type electrode 20 is deposited on the substrate by electron beam evaporation or other methods to serve as the negative electrode of the entire GaN-based laser chip.

[0054] The GaN-based laser chip disclosed in the present invention uses a p-type confinement layer, a current expansion layer and an air layer to form an upper confinement layer. On the one hand, the thickness of the p-type confinement layer can be reduced and its growth time can be shortened, thereby reducing the series resistance of the laser. At the same time, the shortened growth time can also reduce the damage to the quantum well and improve the crystal quality of the GaN-based laser. On the other hand, the introduction of a thin current expansion layer and an air layer with a low refractive index can increase the laser light field confinement, reduce the absorption loss of light by the metal electrode, and ultimately improve the output power and photoelectric conversion efficiency of the GaN-based laser.

[0055] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A GaN-based laser chip, characterized in that: The device comprises, from bottom to top, an n-type electrode (20), a substrate (10), an n-type confinement layer (12), a lower waveguide layer (13), an active layer (14), an upper waveguide layer (15), an upper confinement layer and a p-type electrode (19); The upper confinement layer comprises, from bottom to top, a p-type confinement layer (16), a current spreading layer (17) and an air layer; passivation layers (18) are provided on both sides of the p-type confinement layer (16); the air layer is formed in the middle of the p-type electrode (19); and the orthographic projection of the p-type electrode (19) in the XY plane does not cover the orthographic projection of the p-type confinement layer (16) in the XY plane.

2. The GaN-based laser chip according to claim 1, characterized in that: The material of the p-type confinement layer (16) is AlGaN, the growth temperature is 900-1200°C, and the thickness is 50-200nm; The p-type confinement layer (16) is etched by ICP to form a ridge-shaped region.

3. The GaN-based laser chip according to claim 1, characterized in that: The material of the current spreading layer (17) is ITO or other metal materials with a refractive index lower than that of the p-type limiting layer (16), and the thickness is 10-100 nm; The current spreading layer (17) is formed on the p-type limiting layer (16) by evaporation.

4. The GaN-based laser chip according to claim 1, characterized in that: The material of the passivation layer (18) is silicon dioxide or silicon nitride, and the thickness is the same as that of the p-type confinement layer (16); The passivation layer (18) is formed on both sides of the ridge region of the p-type confinement layer (16) by evaporation.

5. The GaN-based laser chip according to claim 1, characterized in that: The position of the p-type electrode (19) corresponds to the position of the passivation layer (18); The p-type electrode (19) and the n-type electrode (20) are formed by evaporation.

6. The GaN-based laser chip according to claim 1, characterized in that: The active layer (14) is a single quantum well structure or a multi-quantum well structure composed of a quantum well layer and a quantum barrier layer, and the light emission wavelength is 300-600 nm; the growth temperature of the active layer (14) is 700-900° C.; The material of the quantum well layer is one of AlGaN, GaN, InGaN or AlInGaN, and the material of the quantum barrier layer is one of AlGaN, GaN or InGaN.

7. The GaN-based laser chip according to claim 1, characterized in that: The material of the substrate (10) is one of gallium nitride, silicon carbide or silicon.

8. The GaN-based laser chip according to claim 6, characterized in that: The upper waveguide layer (15) is a non-doped upper waveguide layer, and the material is one of InGaN, GaN or AlGaN; The growth temperature of the upper waveguide layer (15) is higher than the growth temperature of the active layer (14).

9. The GaN-based laser chip according to claim 1, characterized in that: A non-doped GaN layer (11) is also included between the substrate (10) and the n-type confinement layer (12).

10. A method for preparing a GaN-based laser chip according to any one of claims 1 to 9, characterized in that: include: S1, sequentially growing an n-type confinement layer (12), a lower waveguide layer (13), an active layer (14), an upper waveguide layer (15), and a p-type confinement layer (16) on a substrate (10); S2, etching to remove the areas on both sides of the p-type restriction layer (16), evaporating a passivation material on the surface of the etched sample, removing excess passivation material above the p-type restriction layer (16), and forming a passivation layer (18) on both sides; S3, performing evaporation deposition on the p-type confinement layer (16) and the passivation layer (18) to form a current spreading layer (17); S4, evaporating a p-type electrode material, removing the p-type electrode material above the p-type limiting layer (16), exposing at least a portion of the current spreading layer (17) to air, and obtaining a p-type electrode (19); wherein the p-type limiting layer (16), the current spreading layer (17) and the air layer together constitute an upper limiting layer; S5, performing vapor deposition under the substrate (10) to form an n-type electrode (20) to obtain a GaN-based laser chip.

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