A semiconductor laser

Abstract

This application proposes a semiconductor laser, comprising: a first nitride semiconductor layer of a first conductivity type; a second nitride semiconductor layer of a second conductivity type; and an active region disposed between the first nitride semiconductor layer and the second nitride semiconductor layer. The active region, from the first nitride semiconductor layer to the second nitride semiconductor layer, sequentially comprises: a first barrier layer, a first insertion layer, a well layer, a second insertion layer, and a second barrier layer. The bandgap width of the first insertion layer is between the first barrier layer and the well layer, and the bandgap width of the second insertion layer is between the second barrier layer and the well layer. The bandgap width of the well layer first decreases and then increases along the epitaxial growth direction. This improves the confinement capability of charge carriers, shortens the transport distance of holes along the gradient energy band, and improves recombination efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and more particularly to a semiconductor laser. Background Technology

[0002] Group III nitride semiconductor materials, represented by InGaN / GaN, can achieve continuous tunability of the bandgap in the ultraviolet to visible light bands by adjusting the In composition. They are the core material system for fabricating blue and green light semiconductor lasers. To address the problems of concentrated carrier distribution, narrow gain spectrum, and strong heterojunction interface polarization effects inherent in traditional square quantum wells, graded-variable-composition quantum wells have been gradually applied to the active region of nitride lasers. In graded-variable-composition quantum wells, the In composition of the well layer changes continuously along the growth direction, resulting in a V-shaped or U-shaped bandgap distribution. This flattens the spatial distribution of carriers within the well and weakens abrupt interface polarization changes, thereby improving the gain characteristics and modulation performance of the device to a certain extent.

[0003] However, existing gradient sub-well structures still face several technical bottlenecks in practical applications that are difficult to balance, thus limiting further improvements in device performance: First, the energy band of the gradient quantum well changes continuously and gradually along the thickness of the well layer. After the charge carriers are injected from the barrier region, they need to relax gradually along the gradient energy band to the recombination center at the bottom of the well. In the nitride material system, the effective mass of the hole is 5 to 10 times that of the electron, and its mobility and energy relaxation rate are much lower than those of the electron. The long-distance gradient transport will significantly prolong the relaxation time of the hole, which will prevent the hole from quickly accumulating to the center of the well to participate in radiative recombination. This will reduce the spatial overlap between electrons and holes, and ultimately limit the performance of the device. Secondly, the barrier layer and the well layer of the gradient carrier well have a continuous energy band transition, and high-energy hot carriers can gradually diffuse along the gradient energy band and escape to the barrier region; especially under high temperature operating conditions, the thermal kinetic energy of the carriers is significantly increased, and the high temperature stability of the device is difficult to guarantee. Summary of the Invention

[0004] In view of the above problems, this application proposes a semiconductor laser, comprising: A first nitride semiconductor layer of a first conductivity type; A second nitride semiconductor layer of the second conductivity type; An active region is disposed between a first nitride semiconductor layer and a second nitride semiconductor layer; The active region, from the first nitride semiconductor layer to the second nitride semiconductor layer, sequentially includes: First barrier layer, first insertion layer, well layer, second insertion layer, second barrier layer; The bandgap width of the first insertion layer is between the first barrier layer and the well layer, and the bandgap width of the second insertion layer is between the second barrier layer and the well layer. The band gap width of the well layer first decreases and then increases along the epitaxial growth direction.

[0005] In some possible implementations, the ratio of the thickness of the first and second insertion layers to the thickness of the well layer is between 0.2 and 0.8.

[0006] In some possible implementations, the ratio of the In component of the first and second insertion layers to the In component of the well layer is between 0.2 and 0.6.

[0007] In some possible implementations, the bandgap width of the second insertion layer is smaller than that of the first insertion layer.

[0008] In some possible implementations, the thickness of the second insertion layer is less than the thickness of the first insertion layer.

[0009] In some possible implementations, the thickness of the first insertion layer is between 1.5 nm and 2.0 nm; The thickness of the second insertion layer is between 0.8 nm and 1.0 nm.

[0010] In some possible implementations, the rate of change of the bandgap width gradually decreases from the interfaces on both sides of the well layer towards the direction where the bandgap width of the well layer is minimized.

[0011] In some possible implementations, along the epitaxial growth direction, the first insertion layer transitions from GaN to InGaN, and the second insertion layer transitions from InGaN to GaN.

[0012] In some possible implementations, the first nitride semiconductor layer is an n-type nitride semiconductor layer, and the second nitride semiconductor layer is a p-type nitride semiconductor layer.

[0013] In some possible implementations, the first barrier layer is GaN. The first insertion layer is In a Ga 1-a N(0 < a < 1), The well layer is In x Ga 1-x N and x first increase and then decrease along the growth direction, and satisfy (a, c < x < 1). The second insertion layer is In c Ga 1-c N(0 < c < 1), The second barrier layer is GaN.

[0014] The beneficial effects of this invention are as follows: An insertion layer with a central bandgap was introduced between the barrier layer and the gradient quantum well to construct a stepped band structure. The intermediate virtual energy state introduced by the insertion layer enabled two-stage adiabatic transitions and phonon-assisted relaxation, shortening the high-resistivity transport distance of holes along the gradient energy band and improving recombination efficiency.

[0015] The insertion layer, which suppresses high-temperature carrier leakage, forms distinct band steps with the barrier and well layers on both sides, blocking the diffusion and escape of high-energy hot carriers into the barrier region. At the same time, the band steps can strongly reflect the carrier wave function in the well, suppressing the penetration of the wave function into the barrier region, enhancing the spatial locality of carriers, significantly reducing leakage current under high-temperature operation, and improving the high-temperature stability and slope efficiency of the device.

[0016] To reduce the difficulty of epitaxial growth and improve the crystal quality and process consistency of the active region, the insertion layer, as a component transition unit between the barrier layer and the high In well layer, can release the strain caused by lattice mismatch step by step, avoid drastic abrupt changes in strain at the interface, and reduce the generation of crystal defects such as mismatch dislocations and In phase separation. Attached Figure Description

[0017] Figure 1 A schematic diagram of a gradually variable sub-trap is disclosed; Figure 2 A schematic diagram of a semiconductor laser is disclosed. Figure 3 A schematic diagram of the structure of an active region is disclosed. Figure 4 A schematic diagram of the bandgap width of an active region is disclosed. Figure 5 A schematic diagram of the bandgap width of the active region is disclosed.

[0018] Figure label: First nitride semiconductor layer: 1; Lower constraint layer: 11; Lower waveguide layer: 12; Second nitride semiconductor layer: 2; Upper waveguide layer: 21; Upper constraint layer: 22; Electron blocking layer: 23; Contact layer: 24 Active region: 3; First barrier layer: 31; First insertion layer: 32; Trap layer: 33; Second insertion layer: 34; Second barrier layer: 35. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0021] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0022] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0023] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0024] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0025] First, the gradient sub-well in the prior art will be described with reference to the accompanying drawings to facilitate understanding of the improvements of the present invention. As shown in Figure 1, Figure 1 is a schematic diagram of the band structure of a V-shaped gradient sub-well in the prior art, with the vertical axis representing the band gap width E. cThe horizontal axis represents the epitaxial growth direction. This type of graded variable child well is widely used in the active regions of optoelectronic devices such as GaN-based nitride semiconductor lasers and light-emitting diodes. Its core structure consists of wide-bandgap barrier layers on both sides and a narrow-bandgap well layer in the middle. The In composition of the well layer continuously increases and then decreases along the epitaxial growth direction, corresponding to a bandgap width that first decreases and then increases along the epitaxial growth direction, resulting in an overall V-shaped bandgap distribution. Some similar structures use a gentler composition change to form a U-shaped graded variable child well.

[0026] Compared with traditional square quantum wells, this gradient quantum well can broaden the gain spectrum range of the device, flatten the spatial distribution of charge carriers in the well, and weaken the polarization charge abrupt change at the heterojunction interface, thus mitigating the influence of the quantum confinement Stark effect. Therefore, it has been widely studied and applied in high-performance lasers.

[0027] However, in practical applications and process implementation, the aforementioned gradient carrier well structure always suffers from problems such as limited carrier relaxation rate, low hole recombination efficiency, insufficient carrier confinement capability, and high difficulty in epitaxial growth.

[0028] To address the aforementioned problems, this application proposes a semiconductor laser, the core of which lies in adding an insertion layer between the gradient sub-well and the potential barriers on both sides. The specific structure and implementation of this invention will be described in detail below.

[0029] Referring to Figure 2, the semiconductor laser in this embodiment is a group III nitride-based semiconductor laser, which includes at least a first nitride semiconductor layer 1 of a first conductivity type, a second nitride semiconductor layer 2 of a second conductivity type, and an active region 3. The active region 3 is disposed between the first nitride semiconductor layer 1 and the second nitride semiconductor layer 2.

[0030] In this embodiment, the first conductivity type is N-type, that is, the first nitride semiconductor layer 1 is an N-type doped nitride semiconductor layer, which can be prepared using Si-doped GaN material, and serves as the electron injection layer of the device for injecting electrons into the active region 3; the second conductivity type is P-type, that is, the second nitride semiconductor layer 2 is a P-type doped nitride semiconductor layer, which can be prepared using Mg-doped GaN material, and serves as the hole injection layer of the device for injecting holes into the active region 3.

[0031] Specifically, the first nitride semiconductor layer 1 is an N-type doped nitride semiconductor stack grown on the upper surface of the substrate, which performs the functions of N-type carrier transport and downward optical field confinement, and includes, from bottom to top: Lower confinement layer 11: Fabricated using N-type doped AlGaN (aluminum gallium nitride) material. This layer has a lower refractive index than the adjacent lower waveguide layer 12, which can form a downward optical confinement for the light field radiated from the active region 3, reducing the leakage of the light field towards the substrate; at the same time, it serves as an N-type carrier conduction channel to inject electron carriers into the active region 3.

[0032] Lower waveguide layer 12: Fabricated using InGaN (indium gallium nitride) material, grown on the upper surface of the lower confinement layer 11. This layer has a higher refractive index than the confinement layers on both the upper and lower sides, and together with the upper waveguide layer 21 on the P-type side, it constitutes the core optical waveguide structure of the device, guiding the light field to propagate laterally along the device, while providing a conduction path for carrier transport.

[0033] The second nitride semiconductor layer 2 is a P-type doped nitride semiconductor stack, grown on the upper surface of the active region 3, and performs the functions of P-type carrier transport, upward optical field confinement, electron blocking, and electrode contact. From bottom to top, it includes: Upper waveguide layer 21: Made of InGaN material, grown on the upper surface of active region 3, and symmetrically distributed with the lower waveguide layer 12 on the N-type side.

[0034] Upper confinement layer 22: Fabricated using P-type doped AlGaN material, grown on the upper surface of upper waveguide layer 21. This layer has a lower refractive index than upper waveguide layer 21, and works in conjunction with lower confinement layer 11 to achieve vertical bidirectional confinement of the optical field.

[0035] Electron blocking layer 23: Fabricated using P-type doped high-aluminum AlGaN material, grown on top of upper confinement layer 22. The conduction band bottom energy level of this layer is significantly higher than that of the active region 3, forming a high-energy electron barrier that effectively prevents electrons in the active region 3 from overflowing towards the P-type layer.

[0036] Contact layer 24: Fabricated using highly concentrated P-type doped GaN material, grown on top of electron blocking layer 23. This layer serves as the ohmic contact layer 24 for the P-type electrode, reducing the contact resistance between the metal electrode and the semiconductor material and ensuring efficient current injection.

[0037] Along the direction of epitaxial growth, such as Figure 3 As shown, from the first nitride semiconductor layer 1 to the second nitride semiconductor layer 2, the active region 3 sequentially includes a first barrier layer 31, a first insertion layer 32, a well layer 33, a second insertion layer 34, and a second barrier layer 35. The first barrier layer 31 is closer to the first nitride semiconductor layer 1, the second barrier layer 35 is closer to the second nitride semiconductor layer 2, and the well layer 33 is located in the middle region between the two insertion layers. The first insertion layer 32 and the second insertion layer 34 serve as transition functional layers between the corresponding barrier layer and the well layer 33.

[0038] The first barrier layer 31 is GaN, and the first insertion layer 32 is In. a Ga 1-a N(0 < a < 1), well layer 33 is In x Ga 1- x N and x first increase and then decrease along the growth direction, and satisfy (a, c < x < 1). The second insertion layer 34 is In. c Ga 1-c N (0 < c < 1), the second barrier layer 35 is GaN.

[0039] like Figure 4 As shown, the bandgap width of the first insertion layer 32 is between the bandgap width of the first barrier layer 31 and the bandgap width of the well layer 33, and the bandgap width of the second insertion layer 34 is between the bandgap width of the second barrier layer 35 and the bandgap width of the well layer 33. In the InGaN / GaN nitride material system, the bandgap width of the material is negatively correlated with the In content: the higher the In content, the narrower the bandgap width. Based on this material characteristic, in this embodiment, the barrier layer uses a wide bandgap nitride material with no or low In content, the insertion layer uses a nitride material with medium In content, and the well layer 33 uses a narrow bandgap nitride material with higher In content, thereby achieving a stepped distribution of the bandgap width and forming a clear bandgap step between the barrier layer and the well layer 33.

[0040] Well layer 33 is a nitride semiconductor layer with a composition that gradually changes along the growth direction. Its bandgap width forms a V-shaped (or U-shaped) shape that first decreases and then increases along the epitaxial growth direction: the In composition of well layer 33 first increases along the epitaxial growth direction, reaches a peak value, and then decreases; correspondingly, the bandgap width first decreases along the epitaxial growth direction, reaches a minimum value, and then increases. In this shape, the bandgap is narrowest in the central region of well layer 33, which is the core region for carrier radiative recombination, and can broaden the gain spectrum of the device and flatten the spatial distribution of carriers within the well.

[0041] Through the aforementioned stepped structure design, this scheme effectively improves the problems of slow carrier relaxation rate, weak carrier confinement capability, and high difficulty in epitaxial growth of traditional fully gradient subwells, while retaining the inherent advantages of gradient subwells. Specifically: An insertion layer with a central band gap was introduced between the barrier layer and the gradient quantum well to construct a stepped band structure. Through the intermediate virtual energy state introduced by the insertion layer, two-stage adiabatic transitions and phonon-assisted relaxation were realized, shortening the high-resistivity transport distance of holes along the gradient energy band.

[0042] A two-stage stepped potential barrier is constructed to enhance carrier confinement and suppress high-temperature carrier leakage. The insertion layer and the barrier layers and well layers on both sides form distinct band steps, blocking the diffusion and escape of high-energy hot carriers into the barrier region. At the same time, the band steps can strongly reflect the carrier wave function in the well, suppressing the penetration of the wave function into the barrier region, enhancing the spatial locality of carriers, significantly reducing leakage current under high-temperature operation, and improving the high-temperature stability and slope efficiency of the device.

[0043] To reduce the difficulty of epitaxial growth and improve the crystal quality and process consistency of the active region 3, the insertion layer serves as a compositional transition unit between the barrier layer and the high In well layer 33. It can release the strain caused by lattice mismatch, avoid drastic abrupt changes in strain at the interface, and reduce the generation of crystal defects such as mismatch dislocations and In phase separation.

[0044] In some embodiments, the ratio of the thickness of the first insertion layer 32 and the second insertion layer 34 to the thickness of the well layer 33 is between 0.2 and 0.8.

[0045] The quantum well of a conventional blue-green laser is 3-6 nm. If the insertion layer is too thick, due to its relatively lower composition compared to the well layer, two distinct localized secondary levels will form on both sides of the active region. Under high current, charge carriers will accumulate locally in the insertion layer (forming ineffective shallow well recombination), thereby causing leakage current and resulting in a decrease in lasing efficiency.

[0046] If the insertion layer is too thin, due to the wave function's penetration effect (Tunneling tailing), the insertion layer will lose its function of blocking electron overflow and trapping holes.

[0047] For example, when the thickness of the well layer 33 is 3 nm, the thicknesses of the first insertion layer 32 and the second insertion layer 34 can be in the range of 0.6 nm to 2.4 nm. In one specific embodiment, the thickness of the well layer 33 is 3 nm, the thickness of the first insertion layer 32 is 1.5 nm, and the thickness of the second insertion layer 34 is 1.0 nm.

[0048] By setting the ratio of the thickness of the first insertion layer 32 and the second insertion layer 34 to the thickness of the well layer 33, the electro-optic and lasing efficiency reduction caused by shallow well recombination can be avoided, and the insertion layers can effectively block electron overflow and trap holes.

[0049] In some embodiments, the ratio of the In component of the first insertion layer 32 and the second insertion layer 34 to the In component of the well layer 33 is between 0.2 and 0.6.

[0050] It should be noted that the In composition in this article refers to the average In composition of the corresponding film layer along the epitaxial growth direction, that is, the arithmetic mean of the In composition of the corresponding film layer over its entire thickness range.

[0051] If the component ratio is too small, the In component of the inserted layer is too low, and its bandgap width is too close to that of the GaN barrier layer. It is impossible to form an effective intermediate bandgap step between the barrier and the well layer 33. There is still a large bandgap abrupt change at the interface, which is difficult to alleviate the barrier drop during carrier injection. At the same time, the buffering effect of the force is greatly weakened, and it is impossible to effectively suppress the segregation of In atoms and the generation of interface defects during the growth process of the well layer 33.

[0052] If the component ratio is too large, the In component of the inserted layer will be too high, and its band gap width will be too close to that of the well layer 33. This will cause the quantum well to significantly reduce its confinement effect on charge carriers, and electrons and holes will easily leak from the well layer 33 to the barrier region, reducing the radiative recombination efficiency of the active region 3.

[0053] By setting the ratio of the In composition of the first insertion layer 32 and the second insertion layer 34 to the In composition of the well layer 33, the overlap integral of the wave function of electrons and holes is increased, thereby improving the internal quantum efficiency of the active region 3.

[0054] In some embodiments, the bandgap width of the second insertion layer 34 is smaller than the bandgap width of the first insertion layer 32.

[0055] In this embodiment, the composition of the first insertion layer 32 on the N side and the second insertion layer 34 on the P side are different. For example, for a blue laser, the In composition of the first insertion layer 32 is between 2% and 4%, and the In composition of the second insertion layer 34 is between 4% and 8%.

[0056] Holes have a large effective mass and a much lower mobility than electrons. When holes are transported from the p-type second nitride semiconductor layer 2 through the second barrier layer 35 to the well layer 33, they are strongly blocked by the valence band barrier. Insufficient hole injection is one of the core bottlenecks limiting the gain improvement of nitride semiconductor lasers. By increasing the In composition of the p-side second insertion layer 34 (for example, by increasing its average In composition to about 6%), the valence band top energy level can be effectively raised, the valence band order between the second barrier layer 35 and the well layer 33 can be reduced, and the valence band barrier height ΔEᵥ of the hole injection active region 3 can be reduced. This significantly improves the hole injection capability and distribution uniformity, makes the hole concentration distribution in the active region 3 more sufficient, improves the spatial matching degree of electrons and holes, and thus improves the radiative recombination efficiency.

[0057] Electrons have a much smaller effective mass than holes, high mobility, and fast transport speed, making them prone to leakage under high current injection conditions. The first insertion layer 32 on the N side uses a relatively lower In composition (for example, its average In composition can be controlled at about 3%), which can keep the N-side conduction band bottom at a relatively high energy level. A gentle conduction band step structure is formed between the first barrier layer 31 and the well layer 33, which forms a stepwise confinement effect on electrons, preventing electrons from directly crossing the active region 3 under high injection, strengthening the binding effect of the quantum well on electrons, and reducing electron leakage loss.

[0058] The refractive index of InGaN material is positively correlated with the In composition. Using a higher In composition in the second insertion layer 34 on the P-side results in a higher refractive index, causing an asymmetric shift of the refractive index profile of the active region 3 towards the P-side along the epitaxial growth direction. This, in turn, pulls the fundamental mode optical field to shift towards the P-side. This optical field modulation effect can optimize the overlap factor between the optical field and the gain region, improving mode gain characteristics. In some embodiments, the thickness of the second insertion layer 34 is less than the thickness of the first insertion layer 32.

[0059] For example, for a blue laser, i.e., with an emission wavelength in the range of 400-500 nm, the thickness of the first insertion layer 32 on the N side is between 1.5 nm and 2.0 nm, and the thickness of the second insertion layer 34 on the P side is between 0.8 nm and 1.0 nm.

[0060] Electrons possess high mobility and long de Broglie wavelengths. Electrons injected from the N-side barrier layer are mostly in a high-energy non-equilibrium state. If they directly enter the well layer 33, they are prone to overflow due to excessive kinetic energy. Setting the thickness of the first insertion layer 32 on the N-side to 1.5nm~2.0nm provides sufficient transport distance for high-energy hot electrons. Before entering the graded well layer 33, they undergo energy relaxation and thermal cooling through multiple scattering with lattice phonons, effectively reducing the average kinetic energy of the electrons. This significantly improves the electron capture efficiency of the quantum well and reduces electron leakage losses under large injection conditions.

[0061] Holes have a large effective mass, and their mobility in low-In-content InGaN materials is much lower than that of electrons. If the thickness of the second insertion layer 34 on the P-side is too large, holes will experience severe transport hindrance and concentration accumulation within the insertion layer, preventing them from tunneling into the light-emitting well region in time. This leads to insufficient hole injection and an imbalance in the electron-hole distribution within the active region 3. Therefore, the thickness of the second insertion layer 34 on the P-side is controlled at a relatively thin level of 0.8 nm to 1.0 nm. This allows it to serve as a quasi-monolithic strain buffer structure to alleviate the lattice mismatch stress at the interface between the barrier layer and the well layer 33, and also as a tunneling transport channel for holes, preventing hole accumulation within the insertion layer and ensuring efficient hole injection into the well region.

[0062] In some embodiments, such as Figure 5 As shown, from the interfaces on both sides of well layer 33 towards the point where the bandgap width of well layer 33 is minimized, the rate of decrease in the bandgap width of well layer 33 gradually decreases. Correspondingly, the In composition of well layer 33 exhibits a nonlinear gradual distribution of "sharp change at both sides and slow change at the center": from the interfaces on both sides of well layer 33 towards the center, the In composition first changes rapidly, then slowly changes to the peak value, forming a non-sharp V-shaped well structure with a gentle bottom of the bandgap, which is different from the conventional gradually changing V-shaped quantum well.

[0063] In this embodiment, as one possible implementation, the thickness of the first insertion layer (N-side insertion layer) is 1.8 nm, with an average In composition of 5%; the thickness of the second insertion layer (P-side insertion layer) is 1.0 nm, with an average In composition of 8%. The total thickness of the well layer is 4 nm, and it is divided into three gradient structures along the epitaxial growth direction: a first gradient segment near the first insertion layer, a central gradual gradient segment, and a second gradient segment near the second insertion layer, with thicknesses of 1 nm, 2 nm, and 1 nm, respectively.

[0064] The first gradient segment (1 nm range on the N side): The In composition rapidly increases from 5% at the junction with the first insertion layer to 15%, with a composition change slope of approximately 10% / nm, belonging to a steep gradient region. Correspondingly, the band gap width in this region decreases rapidly with increasing In composition. The higher composition gradient induces a strong localized polarization electric field, which can quickly drive the electrons newly injected into the well layer towards the center of the well layer, reducing carrier retention at the edge of the well layer and interface nonradiative recombination losses.

[0065] Central Gradually Variation Section (Middle 2nm Range): The In composition gradually increases from 15% to a peak of 17% and then gradually decreases back to 15%, forming a nearly flat high-In, low-bandgap microregion. The equivalent slope of the composition change is approximately 2% / nm, which is a gradually variably changing region. Correspondingly, the rate of decrease in bandgap width is significantly reduced in this region, reaching the minimum bandgap value at the center. This design can reduce the local quantum confinement energy in the central region, avoid the rise of the carrier ground state energy level caused by excessive spatial compression at the bottom of the sharp V-shaped well, and make the peak values ​​of the wave functions of electrons and holes highly coincide in the flat central region, greatly improving the radiative recombination probability. At the same time, the effective width of the high-In composition, high-refractive-index region is widened, which can enhance the local confinement ability of the active region on the optical field and improve the optical confinement factor.

[0066] The second gradient section (1 nm range on the P-side): The In composition rapidly decreases from 15% to 8% at the junction with the second insertion layer, with a composition change slope of approximately 7% / nm, also belonging to the steep gradient region. Correspondingly, the bandgap width in this region increases rapidly as the In composition decreases. The polarization electric field induced by the composition gradient can quickly drive holes towards the center of the well layer. Combined with the design of the high-composition insertion layer on the P-side, this ensures efficient hole injection and transport towards the center.

[0067] This design can simultaneously optimize carrier distribution, radiative recombination efficiency, and optical field confinement characteristics. Its specific effects are as follows: Firstly, a higher composition gradient rate is adopted in the region near the two insertion layers of the well layer 33. The steep In composition gradient induces significant localized polarization charges in this region, forming an additional built-in electric field pointing towards the center of the well layer 33. This built-in electric field can exert a directional transport effect on the electrons and holes newly injected into the well layer 33, rapidly driving the charge carriers to the central luminescent region of the well layer 33, reducing the retention of charge carriers at the edge of the well layer 33 and the non-radiative recombination loss at the interface, and effectively increasing the charge carrier concentration in the central region.

[0068] Secondly, a gentle compositional gradient design is adopted at the center of well layer 33, forming a low-bandgap micro-region with an approximately flat bandgap width, effectively reducing the local quantum confinement energy in the central region. Compared to a sharp linear V-shaped well at the bottom, this design avoids the problem of carrier ground state energy level rise caused by excessive compression of the well bottom space, allowing the wave function peaks of electrons and holes to highly coincide in the flat central region, significantly improving the radiative recombination probability.

[0069] Third, the refractive index of InGaN material is positively correlated with the In composition. The high In composition region in the well layer 33 corresponds to the high refractive index region. The center-gradient design effectively widens the physical width of the high refractive index region, enhances the local confinement capability of the center of the active region 3 on the optical field, can improve the optical confinement factor of the quantum well, and thus improve the mode gain level of the device. This is beneficial to reducing the threshold current density of the laser and improving the output power performance.

[0070] In some embodiments, the composition of the first insertion layer 32 and the second insertion layer 34 is gradually changed, that is, along the epitaxial growth direction, the first insertion layer 32 gradually changes from GaN to InGaN, and the second insertion layer 34 gradually changes from InGaN to GaN.

[0071] For example, the thickness of the first insertion layer 32 on the N side is 2 nm, and its In composition continuously increases from 0 to 0.08 along the epitaxial growth direction, with the material smoothly transitioning from GaN to In. 0.08 Ga 0.92The thickness of the second insertion layer 34 on the N;P side is 1.5 nm, and its In composition continuously decreases from 0.05 to 0 along the epitaxial growth direction. The material is composed of In... 0.05 Ga 0.95 N smoothly transitions to GaN.

[0072] In conventional abrupt heterojunction structures, high-density interfacial polarization surface charges σ_pol accumulate at the interfaces between the GaN barrier and the InGaN insertion layer, and between the InGaN insertion layer and the InGaN well layer 33. This causes severe local band bending in the interface region, forming a steep injection barrier that hinders carrier transport. When the insertion layer adopts a continuous composition gradient design, the polarization surface charges originally concentrated at the two-dimensional interface are transformed into three-dimensional bulk polarization charges ρ_pol(z) distributed along the growth direction, satisfying the distribution law ρ_pol(z) = -dP_pol / dz, where z is the spatial coordinate along the epitaxial growth direction. The spatial dilution of polarization charges can greatly smooth out the severe local band bending, preventing electrons and holes from encountering abrupt barriers during the entire injection process into the active region 3, resulting in a smoother carrier transport process.

[0073] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A semiconductor laser, characterized in that, include: A first nitride semiconductor layer of a first conductivity type; A second nitride semiconductor layer of the second conductivity type; An active region is disposed between the first nitride semiconductor layer and the second nitride semiconductor layer; The active region, from the first nitride semiconductor layer to the second nitride semiconductor layer, sequentially includes: First barrier layer, first insertion layer, well layer, second insertion layer, second barrier layer; The bandgap width of the first insertion layer is between the first barrier layer and the well layer, and the bandgap width of the second insertion layer is between the second barrier layer and the well layer; The band gap width of the well layer first decreases and then increases along the epitaxial growth direction.

2. The semiconductor laser according to claim 1, characterized in that, The ratio of the thickness of the first and second insertion layers to the thickness of the well layer is between 0.2 and 0.

8.

3. The semiconductor laser according to claim 1, characterized in that, The ratio of the In component of the first and second insertion layers to the In component of the well layer is between 0.2 and 0.

6.

4. The semiconductor laser according to claim 1, characterized in that, The band gap width of the second insertion layer is smaller than that of the first insertion layer.

5. The semiconductor laser according to claim 1, characterized in that, The thickness of the second insertion layer is less than the thickness of the first insertion layer.

6. The semiconductor laser according to claim 5, characterized in that, The thickness of the first insertion layer is between 1.5 nm and 2.0 nm; The thickness of the second insertion layer is between 0.8 nm and 1.0 nm.

7. The semiconductor laser according to claim 1, characterized in that, From the interfaces on both sides of the well layer towards the direction where the bandgap width of the well layer is the smallest, the rate of change of the bandgap width of the well layer gradually decreases.

8. The semiconductor laser according to any one of claims 1, characterized in that, Along the epitaxial growth direction, the first insertion layer transitions from GaN to InGaN, and the second insertion layer transitions from InGaN to GaN.

9. The semiconductor laser according to any one of claims 1-8, characterized in that, The first nitride semiconductor layer is an n-type nitride semiconductor layer, and the second nitride semiconductor layer is a p-type nitride semiconductor layer.

10. The semiconductor laser according to any one of claims 1-8, characterized in that, The first barrier layer is GaN. The first insertion layer is In a Ga 1-a N(0 < a < 1), The well layer is In x Ga 1-x N and x first increase and then decrease along the growth direction, and satisfy (a, c < x < 1). The second insertion layer is In c Ga 1-c N(0 < c < 1), The second barrier layer is GaN.

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