Semiconductor laser and preparation method thereof

Abstract

The invention provides a semiconductor laser and a preparation method thereof. The semiconductor laser comprises a lower limiting layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer and an upper limiting layer which are sequentially arranged in a stacked mode in the first direction. The band gap of the upper waveguide layer is gradually increased in the direction from the side, facing the active layer, of the upper waveguide layer to the side, deviating from the active layer, of the upper waveguide layer. The band gap of the upper limiting layer is gradually reduced in the direction from the side, facing the electron blocking layer, of the upper limiting layer to the side, deviating from the electron blocking layer, of the upper limiting layer; the conduction band of the electron blocking layer is higher than the conduction band of the upper waveguide layer and higher than the conduction band of the upper limiting layer, and the conduction band of the electron blocking layer has a band gap difference with the conduction band of the upper waveguide layer and the conduction band of the upper limiting layer. And the output power of the semiconductor laser is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a semiconductor laser and its fabrication method. Background Technology

[0002] Semiconductor lasers emit laser light through radiative recombination of electrons and holes in the active region, generating stimulated emission. Third-generation semiconductor gallium nitride (GaN) and its multi-element alloys, indium gallium nitride (InGaN) and aluminum gallium nitride (AlGaN), are crucial components of semiconductor laser diodes (LDs). GaN-based semiconductor laser diodes cover both blue and green light bands and have significant applications in laser displays, laser projection, laser cutting, underwater laser communication, and atomic clocks.

[0003] The output power of semiconductor lasers based on related technologies needs to be improved. Summary of the Invention

[0004] This application provides a semiconductor laser and a method for fabricating the same, thereby improving the output power of the semiconductor laser.

[0005] To address the aforementioned technical problems, this invention provides a semiconductor laser, comprising: a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer, and an upper confinement layer sequentially stacked along a first direction; wherein, from the side of the upper waveguide layer toward the active layer to the side away from the active layer, the bandgap of the upper waveguide layer increases; and from the side of the upper confinement layer toward the electron blocking layer to the side away from the electron blocking layer, the bandgap of the upper confinement layer decreases; wherein, the conduction band of the electron blocking layer is higher than the conduction band of the upper waveguide layer and higher than the conduction band of the upper confinement layer, and the conduction band of the electron blocking layer has a bandgap difference with the conduction band of the upper waveguide layer and the conduction band of the upper confinement layer, respectively.

[0006] Optionally, the upper waveguide layer contains an In component; the In component in the upper waveguide layer decreases from the side of the upper waveguide layer toward the active layer to the side away from the active layer.

[0007] Optionally, from the side of the upper waveguide layer toward the active layer to the side away from the active layer, the deceleration rate of the In component in the upper waveguide layer increases, or the In component in the upper waveguide layer decreases linearly, or the deceleration rate of the In component in the upper waveguide layer decreases.

[0008] Optionally, the In composition in the upper waveguide layer decreases from a first composition content to a second composition content in a direction from a side of the upper waveguide layer facing the active layer to a side of the upper waveguide layer facing away from the active layer; wherein the first composition content is 3% to 8%.

[0009] Optionally, the second composition content is 0.

[0010] Optionally, the upper confinement layer contains Al composition; the Al composition in the upper confinement layer decreases in a direction from a side of the upper confinement layer facing the electron blocking layer to a side of the upper confinement layer facing away from the electron blocking layer.

[0011] Optionally, the decreasing rate of the Al composition in the upper confinement layer increases in a direction from a side of the upper confinement layer facing the electron blocking layer to a side of the upper confinement layer facing away from the electron blocking layer, or the Al composition in the upper confinement layer decreases linearly, or the decreasing rate of the Al composition in the upper confinement layer decreases.

[0012] Optionally, the electron blocking layer contains Al composition; the Al composition in the upper confinement layer decreases from a third composition content to a fourth composition content in a direction from a side of the upper confinement layer facing the electron blocking layer to a side of the upper confinement layer facing away from the electron blocking layer; wherein the third composition content is less than the Al composition content of the electron blocking layer.

[0013] Optionally, the difference between the Al composition content of the electron blocking layer and the third composition content is 5% to 10% of the Al composition content of the electron blocking layer.

[0014] Optionally, the third composition content is 10% to 20%.

[0015] Optionally, the fourth composition content is 0.

[0016] Optionally, the Al composition content in the electron blocking layer is 10% to 30%.

[0017] Optionally, the band gap difference between the electron blocking layer and the upper confinement layer is 90meV to 185meV.

[0018] Optionally, the thickness of the upper waveguide layer is 50nm to 300nm, the thickness of the electron blocking layer is 5nm to 30nm, and the thickness of the upper confinement layer is 100nm to 200nm.

[0019] Optionally, the semiconductor laser further comprises: an ohmic contact layer located at a side of the upper confinement layer facing away from the electron blocking layer; and an additional optical confinement layer located at a side of the ohmic contact layer facing away from the upper confinement layer.

[0020] Optionally, the thickness of the additional optical confinement layer is 100-300 nm.

[0021] Optionally, the material of the additional optical confinement layer comprises any one of indium tin oxide and doped gallium zinc oxide.

[0022] The application further provides a preparation method of the semiconductor laser, comprising: forming a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer and an upper confinement layer which are sequentially stacked along a first direction; wherein the band gap of the upper waveguide layer increases from the side of the upper waveguide layer facing the active layer to the side of the upper waveguide layer away from the active layer; the band gap of the upper confinement layer decreases from the side of the upper confinement layer facing the electron blocking layer to the side of the upper confinement layer away from the electron blocking layer; wherein the conduction band of the electron blocking layer is higher than the conduction band of the upper waveguide layer and the conduction band of the upper confinement layer, and the conduction band of the electron blocking layer has a band gap difference with the conduction band of the upper waveguide layer and the conduction band of the upper confinement layer respectively.

[0023] The technical scheme has the following technical effects:

[0024] The semiconductor laser provided by the technical scheme is used for improving the electron overflow barrier and blocking the electron overflow in the active layer. Since the band gap of the upper waveguide layer increases from the side of the upper waveguide layer facing the active layer to the side of the upper waveguide layer away from the active layer, the band gap of the side of the upper waveguide layer close to the active layer is small, so that the potential barrier of the side of the upper waveguide layer close to the active layer to the hole is low, and the hole is easily injected from the upper waveguide layer to the active layer. The band gap of the side of the upper waveguide layer away from the active layer is large, so that the potential barrier of the side of the upper waveguide layer away from the active layer to the electron is high, and the electron overflow is better blocked. Since the band gap of the upper confinement layer decreases from the side of the upper confinement layer facing the electron blocking layer to the side of the upper confinement layer away from the electron blocking layer, the band gap of the side of the upper confinement layer away from the electron blocking layer is small, so that the potential barrier of the side of the upper confinement layer away from the electron blocking layer to the hole is low, and the hole is easily injected from the side of the upper confinement layer away from the electron blocking layer to the side of the upper confinement layer facing the electron blocking layer. The band gap of the side of the upper confinement layer close to the electron blocking layer is large, so that the potential barrier of the side of the upper confinement layer close to the electron blocking layer to the electron is high, and the electron overflow is better blocked. The conduction band of the electron blocking layer has a band gap difference with the conduction band of the upper waveguide layer and the conduction band of the upper confinement layer respectively, so that the band gap difference between the electron blocking layer and the upper confinement layer with gradually changing components compensates the interface charge between the electron blocking layer and the upper waveguide layer, a higher electron overflow barrier and a higher hole injection efficiency are obtained, and the internal light loss of the semiconductor laser is reduced. In summary, the light output efficiency and the output power are improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1is a structural schematic diagram of a semiconductor laser provided in an embodiment of the present application;

[0026] Figure 2 is a conduction band diagram of a semiconductor laser in an embodiment of the present application;

[0027] Figure 3 is a valence band diagram of a semiconductor laser in an embodiment of the present application;

[0028] Figure 4 is a schematic diagram of the variation of In component content in the upper waveguide layer in an embodiment of the present application;

[0029] Figure 5 is a schematic diagram of the variation of Al component content in the upper confinement layer in an embodiment of the present application;

[0030] Figure 6 shows the band diagrams of the semiconductor lasers in Example 1, Comparative Example 2 and Comparative Example 3;

[0031] Figure 7 shows the electron concentration distribution and the hole concentration distribution of the semiconductor lasers of Example 1, Comparative Example 2 and Comparative Example 3;

[0032] Figure 8 are the hole concentration spatial distribution map and the electron concentration spatial distribution map of the semiconductor lasers of Comparative Example 3 and Comparative Example 1;

[0033] Figure 9 is the band diagram near the upper waveguide layer of Comparative Example 3 and Comparative Example 1;

[0034] Figure 10 shows the output power-current (P-I) curve and the current-voltage (I-V) curve of the semiconductor laser in the test example and the laser in Comparative Example 3, respectively;

[0035] Figure 11 shows the band diagram of the semiconductor laser of Example 1 and Comparative Example 4, respectively, the interface charge concentration between the upper waveguide layer and the electron blocking layer, the hole concentration in the upper waveguide layer, and the influence of the third component content of the upper confinement layer on the hole concentration in the upper waveguide layer. DETAILED DESCRIPTION

[0036] It is found through research that reducing the hole injection barrier of the semiconductor laser is crucial for optimizing the performance of the semiconductor laser. The use of the Al component gradually varying p-AlGaN upper confinement layer can reduce the hole injection barrier and to a certain extent, can improve the hole injection efficiency.

[0037] However, the semiconductor laser with the single application Al component graded p-AlGaN upper confinement layer without considering the upper waveguide layer and electron blocking layer design has the problem of low hole injection efficiency, and thus is not practical. This is because the application Al component graded p-AlGaN upper confinement layer is not carefully considered the electron overflow barrier, the hole injection barrier and the polarization electric field of the heterojunction interface. Therefore, the size of the electron overflow barrier and the hole injection barrier and the polarization electric field of the heterojunction interface need to be considered comprehensively in the semiconductor laser structure design. The band gap difference between the upper confinement layer and the upper waveguide layer is large, and the steep heterojunction interface has a polarization electric field, which makes the induced charge at the interface hinder the hole injection. In the semiconductor laser with the application Al component graded p-AlGaN upper confinement layer, if the electron blocking layer is not set, it is easy to cause the insufficient electron overflow barrier in the semiconductor laser, and the interface charge between the p-AlGaN upper confinement layer and the upper waveguide layer cannot be compensated, thereby causing the problem of low hole injection efficiency of the semiconductor laser. In summary, the hole injection efficiency of the semiconductor laser is low, and the output power is low.

[0038] On this basis, the technical scheme of the present application provides a semiconductor laser and a preparation method thereof, which improves the hole injection efficiency and improves the output power.

[0039] The technical scheme of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0041] In the description of the application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be mechanically connected, can be electrically connected; can be directly connected, can be indirectly connected through an intermediate medium, can be internal communication of two elements, can be wireless connection, or can be wired connection. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0042] In addition, the technical features involved in the different embodiments of the application described below can be combined with each other as long as there is no conflict.

[0043] An embodiment of the present application provides a semiconductor laser, referring to Figure 1 、 Figure 2 and Figure 3 , comprising:

[0044] a lower confinement layer, a lower waveguide layer 5, an active layer 6, an upper waveguide layer 7, an electron blocking layer 8 and an upper confinement layer 9 are sequentially stacked in a first direction;

[0045] Wherein, from the side of the upper waveguide layer 7 facing the active layer 6 to the side away from the active layer 6, the band gap of the upper waveguide layer 7 increases; from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side away from the electron blocking layer 8, the band gap of the upper confinement layer 9 decreases;

[0046] Wherein, the conduction band of the electron blocking layer 8 is higher than the conduction band of the upper waveguide layer 7 and the conduction band of the upper confinement layer 9, and the conduction band of the electron blocking layer 8 has a band gap difference with the conduction band of the upper waveguide layer 7 and the conduction band of the upper confinement layer 9, respectively.

[0047] In the embodiment, the electron blocking layer 8 is used to improve the electron overflow barrier and block the electron overflow in the active layer 6. Since the band gap of the upper waveguide layer 7 increases from the side of the upper waveguide layer 7 facing the active layer 6 to the side of the upper waveguide layer 7 away from the active layer 6, the band gap of the side of the upper waveguide layer 7 close to the active layer 6 is small, so that the side of the upper waveguide layer 7 close to the active layer 6 has a low potential barrier to holes, facilitating the injection of holes from the upper waveguide layer 7 to the active layer 6. The band gap of the side of the upper waveguide layer 7 away from the active layer 6 is large, so that the side of the upper waveguide layer 7 away from the active layer 6 has a high potential barrier to electrons, better blocking the electron overflow. Since the band gap of the upper confinement layer 9 decreases from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 away from the electron blocking layer 8, the band gap of the side of the upper confinement layer 9 away from the electron blocking layer 8 is small, so that the side of the upper confinement layer 9 away from the electron blocking layer 8 has a low potential barrier to holes, facilitating the injection of holes from the side of the upper confinement layer 9 away from the electron blocking layer 8 to the side of the upper confinement layer 9 facing the electron blocking layer 8, the band gap of the side of the upper confinement layer 9 close to the electron blocking layer 8 is large, so that the side of the upper confinement layer 9 close to the electron blocking layer 8 has a high potential barrier to electrons, better blocking the electron overflow. The conduction band of the electron blocking layer 8 has a band gap difference with the conduction band of the upper waveguide layer 7 and the conduction band of the upper confinement layer 9, respectively, so that the band gap difference between the electron blocking layer and the compositionally-graded upper confinement layer compensates for the interface charge between the electron blocking layer and the upper waveguide layer, achieving a higher electron overflow barrier, a higher hole injection efficiency, and a lower internal optical loss of the semiconductor laser. In summary, the light extraction efficiency and the output power are improved.

[0048] In one embodiment, the upper confinement layer 9 and the lower confinement layer have opposite conduction types. For example, the upper confinement layer 9 has a p-type conduction type, and the lower confinement layer has an n-type conduction type.

[0049] In one embodiment, the upper waveguide layer 7 and the lower waveguide layer 5 have opposite conduction types. For example, the upper waveguide layer 7 has a p-type conduction type, and the lower waveguide layer 5 has an n-type conduction type.

[0050] In one embodiment, the band gap of the electron blocking layer 8 is greater than the band gap of the upper waveguide layer 7. The band gap of the electron blocking layer 8 is greater than the band gap of the upper confinement layer 9.

[0051] In one embodiment, the conduction band of the electron blocking layer 8 has a band gap difference with the conduction band of the upper waveguide layer 7 and the conduction band of the upper confinement layer 9, respectively, which means that the band gap difference between the conduction band of the electron blocking layer 8 and the conduction band of the upper waveguide layer 7 is greater than zero, and the band gap difference between the conduction band of the electron blocking layer 8 and the conduction band of the upper confinement layer 9 is greater than zero.

[0052] In one embodiment, the valence band of the electron blocking layer 8 is lower than the valence band of the upper waveguide layer 7 and lower than the valence band of the upper confinement layer 9. There is a band gap difference between the valence band of the electron blocking layer 8 and the valence band of the upper waveguide layer 7, and there is a band gap difference between the valence band of the electron blocking layer 8 and the valence band of the upper confinement layer 9. The band gap difference between the valence band of the upper waveguide layer 7 and the valence band of the electron blocking layer 8 is greater than zero, and the band gap difference between the valence band of the upper confinement layer 9 and the valence band of the electron blocking layer 8 is greater than zero.

[0053] In one embodiment, the band gap of the upper waveguide layer 7, specifically the height of the conduction band of the upper waveguide layer 7, increases and the height of the valence band of the upper waveguide layer 7 decreases in a direction from a side of the upper waveguide layer 7 facing the active layer 6 to a side of the upper waveguide layer 7 facing away from the active layer 6.

[0054] In one embodiment, the band gap of the upper confinement layer 9, specifically the height of the conduction band of the upper confinement layer 9, decreases and the height of the valence band of the upper confinement layer 9 increases in a direction from a side of the upper confinement layer 9 facing the electron blocking layer 8 to a side of the upper confinement layer 9 facing away from the electron blocking layer 8.

[0055] In one embodiment, the active layer 6 includes quantum well layers and quantum barrier layers which are alternately stacked. The band gap of the quantum barrier layers is greater than the band gap of the quantum well layers.

[0056] In one embodiment, the material of the quantum well layers includes In x9 Ga 1-x9 N, and the material of the quantum barrier layers includes GaN. In one embodiment, x9 is 0.01 to 0.5. For example, 0.1.

[0057] In one embodiment, the thickness of the quantum well layers is 1 nm to 10 nm, for example, 1 nm, and the thickness of the quantum barrier layers is 1 nm to 20 nm, for example, 2 nm.

[0058] The material of the active layer is not limited in the present application. The thickness of the quantum barrier layers and the quantum well layers is not limited.

[0059] In one embodiment, the material of the upper confinement layer 9 includes p-type Al x1 Ga 1-x1 N, where, in one embodiment, x1 is greater than zero and less than or equal to 0.15.

[0060] In one embodiment, the doping concentration of the upper confinement layer 9 is 10 17 atom / cm 3 ~ 10 19 atom / cm 3 , 5 x 10 18 atom / cm 3 .

[0061] In one embodiment, the thickness of the upper confinement layer 9 is 100 nm to 200 nm, for example, 150 nm.

[0062] In one embodiment, the material of the upper waveguide layer 7 includes p-type In x2 Ga 1-x2 N. In one embodiment, the upper waveguide layer 7 is not doped with conductive ions to reduce impurity absorption loss, for example, the material of the upper waveguide layer 7 is undoped In x2 Ga 1-x2 N. In one embodiment, the upper waveguide layer 7 is doped with conductive ions, and the concentration of the conductive ions in the upper waveguide layer 7 is less than the concentration of the conductive ions in the electron blocking layer 8. In one embodiment, x2 is greater than zero and less than or equal to 0.06.

[0063] In one embodiment, the thickness of the upper waveguide layer 7 is 50 nm to 300 nm, for example, 100 nm. When the thickness of the upper waveguide layer is less than 50 nm, it is not conducive to improving the light field confinement of the active layer, and the degree of reduction of the internal light loss of the semiconductor is low. When the thickness of the upper waveguide layer 7 is greater than 300 nm, the degree of improvement of the hole injection efficiency of the semiconductor laser is low.

[0064] In one embodiment, the Al component content in the electron blocking layer 8 is 0.1 to 0.3. The material of the electron blocking layer 8 includes p-type Al x3 Ga 1-x3 N, wherein x3 is 0.1 to 0.3, for example, 0.2.

[0065] In one embodiment, the doping concentration of the electron blocking layer 8 is 10 17 atom / cm 3 ~ 10 19 atom / cm 3 , 5x10 18 atom / cm 3 .

[0066] In one embodiment, the thickness of the electron blocking layer 8 is 5 nm to 30 nm, for example, 20 nm. When the thickness of the electron blocking layer 8 is less than 5 nm, the probability of electron tunneling through the electron blocking layer 8 is high, which is not conducive to the blocking of the electron blocking layer 8 to the electrons. When the thickness of the electron blocking layer 8 is greater than 30 nm, the degree of improvement of the hole injection efficiency is low.

[0067] In one embodiment, the lower confinement layer includes a first sub-lower confinement layer 2 and a second sub-lower confinement layer 4. The refractive index of the first sub-lower confinement layer 2 is less than the refractive index of the second sub-lower confinement layer 4. The semiconductor laser further includes an insertion layer 3 located between the first sub-lower confinement layer and the second sub-lower confinement layer. The first sub-lower confinement layer 2 is located on the side of the second sub-lower confinement layer 4 away from the active layer 6.

[0068] In one embodiment, the material of the first sub-confinement layer 2 is n-type Al x4 Ga 1-x4 N, and the material of the second sub-confinement layer 4 is n-type Al x5 Ga 1-x5 N. Wherein, the size relationship of x4 and x5 is x4 < x5. x4 is 0.01-0.04, for example, 0.02. x5 is 0.05-0.08, for example, 0.07.

[0069] In one embodiment, the doping concentration of the first sub-confinement layer 2 is greater than the doping concentration of the second sub-confinement layer 4. The effects include: the second sub-confinement layer 4 is closer to the active layer 6 relative to the first sub-confinement layer 2, closer to the center of the light field, the doping concentration of the second sub-confinement layer 4 is lower, reducing the impurity absorption coefficient and thus reducing the optical loss; the first sub-confinement layer 2 is far from the center of the light field, the internal light field of the first sub-confinement layer 2 is weak, even if the absorption coefficient increases, the total absorption loss is relatively small, so the doping concentration of the first sub-confinement layer 2 can be increased to reduce the series resistance, so as to achieve lower working voltage.

[0070] In one embodiment, the thickness of the first sub-confinement layer 2 is 800nm-1600nm, for example, 1000nm.

[0071] In one embodiment, the doping concentration of the first sub-confinement layer 2 is 1×10 17 atom / cm 3 -1×10 19 atom / cm 3 , for example, 5×10 17 atom / cm 3 .

[0072] In one embodiment, the thickness of the second sub-confinement layer 4 is 400nm-800nm, for example, 500nm.

[0073] In one embodiment, the doping concentration of the second sub-confinement layer 4 is 1×10 17 atom / cm 3 -1×10 19 atom / cm 3 , for example, 1×10 18 atom / cm 3 .

[0074] In one embodiment, the band gap of the insertion layer 3 is between the first sub-confinement layer 2 and the second sub-confinement layer 4. The conductivity type of the insertion layer 3 is the same as that of the lower confinement layer.

[0075] In one embodiment, the material of the insertion layer 3 is n-type Inx6 Ga 1-x6 N. x6 is 0.02 to 0.06, for example, 0.04.

[0076] In one embodiment, the thickness of the insertion layer 3 is 80nm to 200nm, for example, 100nm.

[0077] In one embodiment, the doping concentration of the insertion layer 3 is 1×10⁻⁶. 17 atom / cm 3 ~1×10 19 atom / cm 3 For example, 5×10 17 atom / cm 3 .

[0078] In one embodiment, the lower confining layer is a single-layer structure. For example, the material of the lower confining layer is n-type Al. x7 Ga 1-x7 N, x7 is 0.02 to 0.10.

[0079] In one embodiment, the material of the lower waveguide layer 5 includes n-type In x8 Ga 1-x8 N. In one embodiment, the lower waveguide layer 5 is not doped with conductive ions to reduce impurity absorption loss; for example, the material of the lower waveguide layer 5 is undoped In. x8 Ga 1-x8 N. In one embodiment, the lower waveguide layer 5 is doped with conductive ions, and the concentration of conductive ions in the lower waveguide layer 5 is less than the concentration of conductive ions in the lower confinement layer. Here, x8 is 0.01 to 0.06, for example, 0.04.

[0080] In one embodiment, the thickness of the lower waveguide layer 5 is 80nm to 300nm, for example, 150nm.

[0081] In one embodiment, the upper waveguide layer 7 contains an In component; the In component in the upper waveguide layer 7 decreases from the side of the upper waveguide layer 7 toward the active layer 6 to the side away from the active layer 6.

[0082] In one embodiment, the refractive index of the upper waveguide layer 7 decreases from the side of the upper waveguide layer 7 toward the active layer 6 to the side of the upper waveguide layer 7 away from the active layer 6.

[0083] In one embodiment, reference Figure 4 From the side of the upper waveguide layer 7 toward the active layer 6 to the side away from the active layer 6, the deceleration rate of the In component in the upper waveguide layer 7 increases, or the In component in the upper waveguide layer 7 decreases linearly, or the deceleration rate of the In component in the upper waveguide layer 7 decreases.Figure 4 the horizontal axis is the position in the first direction, Figure 4 the vertical axis is the In composition content of the upper waveguide layer.

[0084] When the decreasing rate of the In composition in the upper waveguide layer 7 increases from the side of the upper waveguide layer 7 facing the active layer 6 to the side of the upper waveguide layer 7 facing away from the active layer 6, that is, the In composition in the upper waveguide layer 7 decreases first slowly and then quickly, the average In composition in the upper waveguide layer 7 is higher, and the average refractive index of the upper waveguide layer 7 is higher, which is conducive to increasing the refractive index difference between the upper waveguide layer 7 and the upper confinement layer 9 and improving the light field confinement.

[0085] In one embodiment, the In composition in the upper waveguide layer 7 decreases from a first composition content to a second composition content from the side of the upper waveguide layer 7 facing the active layer 6 to the side of the upper waveguide layer 7 facing away from the active layer 6; wherein the first composition content is 3% to 8%, for example, 6%; preferably, the second composition content is 0. In other embodiments, the second composition content can be greater than zero.

[0086] In one embodiment, the first composition content is less than the maximum value of the In composition content in the active layer 6.

[0087] In one embodiment, the upper confinement layer 9 contains Al composition; the Al composition in the upper confinement layer 9 decreases from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 facing away from the electron blocking layer 8.

[0088] In one embodiment, the refractive index of the upper confinement layer 9 increases from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 facing away from the electron blocking layer 8.

[0089] In one embodiment, with reference to Figure 5 the decreasing rate of the Al composition in the upper confinement layer 9 increases from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 facing away from the electron blocking layer 8, or the Al composition in the upper confinement layer 9 decreases linearly, or the decreasing rate of the Al composition in the upper confinement layer 9 decreases. Figure 5 the horizontal axis is the position in the first direction, Figure 5 the vertical axis is the Al composition content of the upper confinement layer.

[0090] The rate of decrease of the Al component in the upper confinement layer 9 increases from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 facing away from the electron blocking layer 8, that is, the rate of decrease of the Al component in the upper confinement layer 9 is slow at first and then fast, and the average Al component of the upper confinement layer 9 is higher, so that the average refractive index of the upper confinement layer 9 is lower, which is conducive to improving the restriction on the light field. The high rate of change of the Al component in the region of the side of the upper confinement layer 9 facing away from the electron blocking layer 8 can increase the concentration of the polarization charge in the region of the side of the upper confinement layer 9 facing away from the electron blocking layer 8, thereby increasing the surface hole concentration. The high hole concentration on the surface of the side of the upper confinement layer 9 facing away from the electron blocking layer 8 is conducive to forming a good ohmic contact.

[0091] In one embodiment, the rate of decrease of the In component in the upper waveguide layer 7 increases from the side of the upper waveguide layer 7 facing the active layer 6 to the side of the upper waveguide layer 7 facing away from the active layer 6, and the rate of decrease of the Al component in the upper confinement layer 9 increases from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 facing away from the electron blocking layer 8. This effectively improves the restriction on the light field.

[0092] In one embodiment, the electron blocking layer 8 comprises an Al component; the Al component in the upper confinement layer 9 decreases from a third component content to a fourth component content from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side of the upper confinement layer 9 facing away from the electron blocking layer 8; and the third component content is less than the Al component content of the electron blocking layer.

[0093] In one embodiment, the difference between the Al component content of the electron blocking layer 8 and the third component content is 5% to 10% of the Al component content of the electron blocking layer 8.

[0094] In one embodiment, the third component content is 10% to 20%, for example, 15%.

[0095] In one embodiment, the fourth component content is 0. In other embodiments, the fourth component content is greater than zero.

[0096] In one embodiment, the difference between the conduction band of the electron blocking layer 8 and the conduction band of the upper confinement layer 9 is 90 meV to 185 meV.

[0097] In one embodiment, the conduction band of the side of the upper confinement layer 9 facing the electron blocking layer 8 is higher than the conduction band of the side of the upper waveguide layer 7 facing the electron blocking layer 8. The conduction band of the side of the upper confinement layer 9 facing away from the electron blocking layer 8 is higher than the conduction band of the side of the upper waveguide layer 7 facing the electron blocking layer 8, and the conduction band of the side of the upper confinement layer 9 facing away from the electron blocking layer 8 is higher than the conduction band of the side of the upper waveguide layer 7 facing away from the electron blocking layer 8.

[0098] In one embodiment, the valence band of the upper confinement layer 9 on the side facing the electron blocking layer 8 is lower than the valence band of the upper waveguide layer 7 on the side facing the electron blocking layer 8. The valence band of the upper confinement layer 9 on the side facing away from the electron blocking layer 8 is lower than the valence band of the upper waveguide layer 7 on the side facing the electron blocking layer 8. The valence band of the upper confinement layer 9 on the side facing away from the electron blocking layer 8 is lower than the valence band of the upper waveguide layer 7 on the side facing away from the electron blocking layer 8.

[0099] In one embodiment, the semiconductor laser further comprises an ohmic contact layer 10 on the side of the upper confinement layer 9 facing away from the electron blocking layer 8; and an additional optical confinement layer 11 on the side of the ohmic contact layer 10 facing away from the upper confinement layer 9. The semiconductor laser further comprises a front electrode layer 12 on the side of the additional optical confinement layer 11 facing away from the ohmic contact layer 10.

[0100] In one embodiment, the material of the ohmic contact layer 10 is a doped semiconductor material, for example, the material of the ohmic contact layer 10 is p-type GaN.

[0101] In one embodiment, the thickness of the ohmic contact layer 10 is 5 nm to 30 nm, for example, 5 nm.

[0102] In one embodiment, the doping concentration of the ohmic contact layer 10 is 10 17 atom / cm 3 to 10 19 atom / cm 3 , for example, 5 x 10 17 atom / cm 3 .

[0103] The ohmic contact layer 10 can reduce the contact resistance of the upper confinement layer 9 and the additional optical confinement layer 11.

[0104] The conductivity of the additional optical confinement layer 11 is greater than the conductivity of the ohmic contact layer 10, and the conductivity of the ohmic contact layer 10 is greater than the conductivity of the upper confinement layer 9.

[0105] In one embodiment, the material of the additional optical confinement layer 11 includes any one of indium tin oxide and doped gallium zinc oxide.

[0106] In one embodiment, the thickness of the additional optical confinement layer 11 is 100 nm to 300 nm, for example, 150 nm.

[0107] The additional optical confinement layer 11 can greatly reduce the internal optical loss of the semiconductor laser, thereby significantly improving the performance of the laser.

[0108] In one embodiment, the material of the front electrode layer 12 is metal, for example, Ti.

[0109] In one embodiment, the thickness of the front electrode layer 12 is 80 nm to 1000 nm, for example, 500 nm.

[0110] In one embodiment, the semiconductor laser further comprises: a substrate layer 1 located on the side of the lower confinement layer 3 away from the lower waveguide layer 2; and a back electrode 14 located on the side of the substrate layer 1 away from the lower confinement layer 3.

[0111] In one embodiment, the thickness of the substrate layer 1 is 300 μm to 1000 μm, for example, 450 μm.

[0112] In one embodiment, the substrate layer 1 is of n-type, and the doping concentration in the substrate layer 1 is 5 x 1017 atom / cm3 to 3 x 1018 atom / cm3, for example, 1 x 1018 atom / cm3. 17 3 19 3 19 3

[0113] In one embodiment, the thickness of the back electrode 14 is 100 nm to 1000 nm, for example, 500 nm.

[0114] In one embodiment, the material of the back electrode 14 is metal, for example, Ti.

[0115] Further, the semiconductor laser emits light in the wavelength range from violet to yellow.

[0116] In one embodiment, the upper confinement layer 9 is located on the side of the partial electron blocking layer 8 away from the upper waveguide layer 7, and the upper confinement layer 9, the ohmic contact layer 10, and the additional optical confinement layer 11 form a ridge structure. The semiconductor laser further comprises: a passivation layer 13 located on the sidewall of the ridge structure and the side of the partial electron blocking layer 8 away from the upper waveguide layer 7. The material of the passivation layer 13 comprises silicon oxide.

[0117] Test Example

[0118] In one of the test examples, a GaN-based semiconductor laser, in the direction from the side of the upper waveguide layer 7 facing the active layer 6 to the side away from the active layer 6, the In component in the upper waveguide layer 7 decreases from a first component content to a second component content; wherein the first component content is 6%, and the second component content is 0; in the direction from the side of the upper confinement layer 9 facing the electron blocking layer 8 to the side away from the electron blocking layer 8, the Al component in the upper confinement layer 9 decreases from a third component content to a fourth component content, the third component content is 15%, and the fourth component content is 0. The Al component in the electron blocking layer is uniformly distributed, and the Al component content in the electron blocking layer is 20%.

[0119] Comparative Example 1​​​​​​

[0120] The GaN-based semiconductor laser in Comparative Example 1 has the In composition in the upper waveguide layer uniformly distributed, the In composition content in the upper waveguide layer being 3%, the Al composition in the electron blocking layer uniformly distributed, the Al composition content in the electron blocking layer being 20%, and the Al composition in the upper confinement layer 9 uniformly distributed, the Al composition content in the upper confinement layer being 3.5%. The rest of the structure is the same as in the test example.

[0121] Comparative Example 2

[0122] The GaN-based semiconductor laser in Comparative Example 2 has the structure different from the test example in that the electron blocking layer in the test example is cancelled, and the upper waveguide layer in Comparative Example 2 has the In composition uniformly distributed, the In composition content in the upper waveguide layer being 3%, which is the same as the upper waveguide layer in Comparative Example 1. The rest of the structure in Comparative Example 2 is the same as in the test example.

[0123] Comparative Example 3

[0124] The GaN-based semiconductor laser in Comparative Example 3 is different from the test example in that the Al composition in the upper confinement layer is uniformly distributed, the Al composition content in the upper confinement layer 9 being 3.5%. The rest of the structure is the same as in the test example.

[0125] Comparative Example 4

[0126] The GaN-based semiconductor laser in Comparative Example 4 is different from the test example in that the Al composition in the upper confinement layer 9 decreases from the third composition content to the fourth composition content, the third composition content being 20%, and the Al composition content in the electron blocking layer being 20%. The rest of the structure is the same as in the test example.

[0127] The inventors have found through theoretical research and software simulation that if there is no band gap difference between the electron blocking layer and the upper confinement layer, the hole injection efficiency is significantly inhibited, which damages the performance of the semiconductor laser. See Table 1 for details.

[0128] Table 1

[0129]

[0130]

[0131] As can be seen from Table 1, compared with the laser structure (Comparative Example 1) having the upper waveguide layer with uniform composition and the upper confinement layer with uniform composition, the semiconductor laser in the test example of the present application has an electron overflow barrier increased by about 15 meV and a hole injection barrier decreased by 79 meV.

[0132] Figure 6Band diagrams of the semiconductor lasers in Example 1, Comparative Example 2 and Comparative Example 3 are shown, and the sizes of the corresponding electron overflow barrier and hole injection barrier are marked. Figure 6 a shows the band diagram of the semiconductor laser of Example 1, Figure 6 b shows the band diagram of the semiconductor laser of Comparative Example 2, Figure 6 c shows the band diagram of the semiconductor laser of Comparative Example 3. Figure 6 a, Figure 6 b and Figure 6 c the horizontal axis is the position in the first direction, Figure 6 a, Figure 7 b and Figure 7 c the vertical axis is the band energy of the semiconductor laser. Figure 7 Electron concentration distribution and hole concentration distribution of the semiconductor lasers of Example 1, Comparative Example 2 and Comparative Example 3 are shown, Figure 7 a shows the hole concentration distribution of the semiconductor lasers of Example 1, Comparative Example 2 and Comparative Example 3, Figure 7 b shows the electron concentration distribution of the semiconductor lasers of Example 1, Comparative Example 2 and Comparative Example 3. Figure 7 a and Figure 7 b the horizontal axis is the position in the first direction, Figure 6 a the vertical axis is the hole concentration of the semiconductor laser, Figure 8 b the vertical axis is the electron concentration of the semiconductor laser. It can be seen that the semiconductor laser in the test example of improved hole injection efficiency has the least electron leakage and the highest hole injection efficiency. Therefore, it can be known that the band gap difference between the electron blocking layer 8 and the upper cladding layer 9 with gradually changing Al composition is very important, and this design maintains a high enough electron overflow barrier to prevent more electrons from overflowing to the upper cladding layer 9.

[0133] As shown in Figure 8 , the upper waveguide layer 7 with gradually changing In composition has a polarization electric field that is beneficial to hole injection compared to the conventional upper waveguide layer with uniform composition, and in the direction away from the active layer 6, the band gap of the upper waveguide layer 7 gradually increases, which has the effect of reducing the number of electrons from the upper waveguide layer 7 across the electron blocking layer 8, and in addition, it also has the effect of improving the optical confinement factor of the active layer.

[0134] The present application also compares the effects of the upper waveguide layer with gradually changing In composition and the upper waveguide layer with uniform In composition on hole injection, Figure 8 the hole concentration spatial distribution graph and the electron concentration spatial distribution graph of the semiconductor laser based on the upper waveguide layer with gradually changing In composition and the upper waveguide layer with uniform In composition, Figure 8 a is the hole concentration spatial distribution graph of the semiconductor laser based on the upper waveguide layer with gradually changing In composition and the upper waveguide layer with uniform In composition, Figure 8b is a spatial distribution map of the electron concentration of the laser of the upper waveguide layer with the In composition gradient and the uniform In composition. Figure 8 a and Figure 8 The horizontal axis of b is the position in the first direction, Figure 9 The vertical axis of a is the hole concentration of the semiconductor laser, Figure 9 The vertical axis of b is the electron concentration of the semiconductor laser. Figure 9 is a band diagram near the upper waveguide layer of Comparative Example 3 and Comparative Example 1, Figure 9 is a band diagram of the semiconductor laser of the upper waveguide layer with the In composition gradient and the uniform In composition. Figure 8 The horizontal axis of b is the position in the first direction, Figure 8 The vertical axis of b is the band energy.

[0135] Figure 9 a, Figure 8 b and Figure 8 The advantages of the upper waveguide layer with the In composition gradient compared with the upper waveguide layer with the uniform In composition are compared in detail in b. Figure 10 a and Figure 10 b respectively show the influence of the two kinds of upper waveguide layers on the spatial distribution of the hole concentration and the electron concentration in the semiconductor laser, it can be seen that the upper waveguide layer with the In composition gradient is beneficial to reduce the number of electrons crossing the electron blocking layer, improve the hole injection efficiency, and the In composition gradient makes the polarized electric field exist in the upper waveguide layer which is beneficial to hole injection. The simulation results show that the number of holes injected into the active layer is increased, which all indicates that the upper waveguide layer with the In composition gradient is beneficial to improve the hole injection efficiency of the semiconductor laser.

[0136] Figure 10 a is the output power-current (P-I) curve of the semiconductor laser in the test example and the semiconductor laser in Comparative Example 3, Figure 10 b is the current-voltage (I-V) curve of the semiconductor laser in the test example and the semiconductor laser in Comparative Example 3. It can be learned that the semiconductor laser with improved hole injection efficiency in the test example of the application obtains a lower threshold current density and the highest slope efficiency. From the I-V curve, it can be seen that the improved hole injection efficiency in the test example of the application makes the working voltage of the semiconductor laser lower. Figure 10 a and Figure 10 The horizontal axis of b is the current, Figure 11 The vertical axis of a is the output power, Figure 11 The vertical axis of b is the voltage.

[0137] Figure 11a shows the band diagram of the semiconductor laser in the test example and the semiconductor laser in Comparative Example 4, it can be seen that although there is no band gap difference between the electron blocking layer and the upper confining layer in the semiconductor laser of Comparative Example 4, the hole injection barrier in Comparative Example 4 becomes very low. In fact, if the band gap of the upper confining layer is smaller than that of the electron blocking layer, the interface between the upper confining layer and the electron blocking layer will generate opposite polarization charges to compensate the polarization charges between the electron blocking layer and the upper waveguide layer. However, in Comparative Example 4, the Al composition of the electron blocking layer and the starting composition of the Al composition graded upper confining layer are both 20%, and the polarization charges between the electron blocking layer and the In composition graded upper waveguide layer cannot be compensated. Figure 11 b shows the electron concentration at the interface between the upper waveguide layer and the electron blocking layer, the electron concentration at the interface between the upper waveguide layer and the electron blocking layer of Comparative Example 4 is higher, which directly leads to Figure 11 c shows that the hole concentration in Comparative Example 4 that crosses the electron blocking layer 8 into the In composition graded upper waveguide layer is lower. Figure 11 c is a schematic diagram of the hole concentration in the upper waveguide layer.

[0138] Figure 11 d shows the effect of the third composition content of the upper confining layer on the hole concentration in the upper waveguide layer, in Figure 11 d shows that the hole concentration entering the In composition graded upper waveguide layer changes in a circular arc shape with the third composition content of the Al composition graded upper confining layer 9, and the third composition content of 15% is optimal, but the third composition content within the range of 10% to 20% also has good results.

[0139] Figure 11 The horizontal axis of a is the position in the first direction, Figure 11 The vertical axis of a is the band energy. Figure 11 The horizontal axis of b is the position in the first direction, Figure 11 The vertical axis of b is the interface charge concentration between the upper waveguide layer and the electron blocking layer. Figure 11 The horizontal axis of c is the position in the first direction, Figure 11 The vertical axis of c is the hole concentration in the upper waveguide layer. ​ The horizontal axis of d is the third composition content, ​ The vertical axis of d is the hole concentration in the upper waveguide layer.

[0140] It should be understood that the above embodiments are only to illustrate the technical concepts and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A semiconductor laser, characterized in that, include: The lower confinement layer, lower waveguide layer, active layer, upper waveguide layer, electron blocking layer and upper confinement layer are stacked sequentially along the first direction; Specifically, the bandgap of the upper waveguide layer increases from the side of the upper waveguide layer toward the active layer to the side of the upper waveguide layer away from the active layer; the bandgap of the upper confinement layer decreases from the side of the upper confinement layer toward the electron blocking layer to the side of the upper confinement layer away from the electron blocking layer. The conduction band of the electron blocking layer is higher than the conduction band of the upper waveguide layer and higher than the conduction band of the upper confinement layer, and the conduction band of the electron blocking layer has a bandgap difference with the conduction band of the upper waveguide layer and the conduction band of the upper confinement layer, respectively.

2. The semiconductor laser according to claim 1, characterized in that, The upper waveguide layer contains an In component; the In component in the upper waveguide layer decreases from the side of the upper waveguide layer toward the active layer to the side away from the active layer.

3. The semiconductor laser according to claim 2, characterized in that, From the side of the upper waveguide layer toward the active layer to the side away from the active layer, the deceleration rate of the In component in the upper waveguide layer increases, or the In component in the upper waveguide layer decreases linearly, or the deceleration rate of the In component in the upper waveguide layer decreases.

4. The semiconductor laser according to claim 2, characterized in that, From the side of the upper waveguide layer toward the active layer to the side away from the active layer, the In content in the upper waveguide layer decreases from the content of the first component to the content of the second component; wherein, the content of the first component is 3% to 8%; Preferably, the content of the second component is 0.

5. The semiconductor laser according to claim 1, characterized in that, The upper confinement layer contains an Al component; the Al component in the upper confinement layer decreases from the side of the upper confinement layer toward the electron blocking layer to the side away from the electron blocking layer.

6. The semiconductor laser according to claim 5, characterized in that, From the side of the upper confinement layer toward the electron blocking layer to the side away from the electron blocking layer, the deceleration rate of the Al component in the upper confinement layer increases, or the deceleration rate of the Al component in the upper confinement layer decreases linearly, or the deceleration rate of the Al component in the upper confinement layer decreases.

7. The semiconductor laser according to claim 5, characterized in that, The electron blocking layer contains an Al component; from the side of the upper confining layer toward the electron blocking layer to the side away from the electron blocking layer, the Al component content in the upper confining layer decreases from the third component content to the fourth component content; wherein, the third component content is less than the Al component content of the electron blocking layer; Preferably, the difference between the Al component content of the electron blocking layer and the content of the third component is 5% to 10% of the Al component content of the electron blocking layer; Preferably, the content of the third component is 10% to 20%; Preferably, the content of the fourth component is 0; Preferably, the Al component content in the electron blocking layer is 10% to 30%.

8. The semiconductor laser according to claim 1, characterized in that, The band gap difference between the electron blocking layer and the upper confinement layer is 90 meV to 185 meV.

9. The semiconductor laser according to claim 1, characterized in that, The thickness of the upper waveguide layer is 50nm to 300nm, the thickness of the electron blocking layer is 5nm to 30nm, and the thickness of the upper confinement layer is 100nm to 200nm.

10. The semiconductor laser according to claim 1, characterized in that, The semiconductor laser further includes: an ohmic contact layer located on the side of the upper confinement layer opposite to the electron blocking layer; An additional optical confinement layer is located on the side of the ohmic contact layer opposite to the upper confinement layer; Preferably, the thickness of the additional optical confinement layer is 100 nm to 300 nm; Preferably, the material of the additional optical confinement layer includes either indium tin oxide or doped gallium zinc oxide.

11. A method for fabricating a semiconductor laser as described in any one of claims 1 to 10, characterized in that, include: A lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer, and an upper confinement layer are formed and stacked sequentially along the first direction; Specifically, the bandgap of the upper waveguide layer increases from the side of the upper waveguide layer toward the active layer to the side of the upper waveguide layer away from the active layer; the bandgap of the upper confinement layer decreases from the side of the upper confinement layer toward the electron blocking layer to the side of the upper confinement layer away from the electron blocking layer. The conduction band of the electron blocking layer is higher than the conduction band of the upper waveguide layer and higher than the conduction band of the upper confinement layer, and the conduction band of the electron blocking layer has a bandgap difference with the conduction band of the upper waveguide layer and the conduction band of the upper confinement layer, respectively.

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