Trapezoidal electrode edge-emitting wide-surface low-coherence semiconductor laser

Abstract

The invention provides a trapezoid electrode edge-emitting wide-surface low-coherence semiconductor laser. The trapezoid electrode edge-emitting wide-surface low-coherence semiconductor laser comprises a substrate layer; the n limiting layer, the n waveguide layer, the quantum well active region, the p waveguide layer, the p limiting layer, the p contact layer and the insulating layer are sequentially stacked on the first surface of the substrate layer; wherein mesa structures are formed in the p contact layer and the p limiting layer in the cavity length direction of the semiconductor laser, isolation grooves are formed in the two sides of each mesa structure, rectangular grooves which are arranged periodically are formed in the mesa structures in the cavity length direction of the semiconductor laser, and trapezoidal electrodes are formed in the protruding parts of the mesa structures. An electric contact window is formed in an area corresponding to the trapezoidal electrode on the insulating layer, and the trapezoidal electrode is used for current injection; the P-surface electrode is formed on the insulating layer and penetrates through the electric contact window to be connected with the trapezoidal electrode; and the N-surface electrode forms the second surface of the substrate layer. According to the device, high-directivity low-coherence continuous high-power output is realized, and the electro-optical conversion efficiency is close to that of a common edge-emitting wide-surface semiconductor laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic devices, specifically to a trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser. Background Technology

[0002] Semiconductor lasers possess advantages such as small size, high electro-optical conversion efficiency, long lifespan, and small optical expansion, leading to their wide application in lighting displays, industrial processing, medical applications, and communications. However, the light emitted by lasers typically exhibits strong coherence. When coherent light illuminates a rough object, its scattered light undergoes random interference at the image plane, producing speckles of varying brightness and size. In the field of lighting displays, the presence of speckles severely interferes with image quality, hindering the direct application of semiconductor lasers.

[0003] The most fundamental way to suppress speckle is to reduce the coherence of the laser at its source. The temporal coherence of a laser is primarily determined by its spectral bandwidth. Due to the inherent characteristics of stimulated emission and mode competition, semiconductor lasers typically exhibit narrow-band emission and high temporal coherence. The spatial coherence of a laser is closely related to the transverse mode number of the lasing. For wide-area semiconductor lasers, the active region size can reach hundreds of micrometers, supporting multi-transverse mode lasing. Compared to surface-emitting wide-area semiconductor lasers, edge-emitting wide-area semiconductor lasers have higher output power and electro-optical conversion efficiency, making them more suitable for laser lighting and display applications.

[0004] Currently, edge-emitting wide-area low-coherence semiconductor lasers are mainly realized through chaotic microcavities. By optimizing the shape of the active region waveguide, the resonant cavity can support a large number of chaotic mode lasings, thereby reducing the spatial coherence of the output laser. However, chaotic modes are usually non-axial, with far-field divergence angles exceeding 70°, resulting in poor directivity of such lasers. On the other hand, the sidewalls of chaotic microcavities typically contain arc-shaped structures, and the arc-shaped structures prepared by photolithography have a certain surface roughness, which introduces significant scattering losses. The overall electro-optical conversion efficiency of chaotic microcavity lasers is not high, and they can usually only operate in pulsed mode. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser, which at least partially solves the aforementioned technical problems.

[0006] This invention provides a trapezoidal electrode-based edge-emitting wide-area low-coherence semiconductor laser, comprising: a substrate layer; an n-confinement layer, an n-waveguide layer, a quantum well active region, a p-waveguide layer, a p-confinement layer, a p-contact layer, and an insulating layer sequentially stacked on a first surface of the substrate layer; wherein, a mesa structure is formed in the p-contact layer and the p-confinement layer along the length of the semiconductor laser cavity, isolation grooves are formed on both sides of the mesa structure, and periodically arranged rectangular grooves are formed in the mesa structure along the length of the semiconductor laser cavity, and a trapezoidal electrode is formed on the protruding portion of the mesa structure, and an electrical contact window is formed in the region corresponding to the trapezoidal electrode on the insulating layer, the trapezoidal electrode being used for current injection; a p-surface electrode is formed on the insulating layer and passes through the electrical contact window to connect with the trapezoidal electrode; an n-surface electrode forms a second surface of the substrate layer, the first surface and the second surface being opposite each other.

[0007] The trapezoidal electrode edge-emitting wide-area low-coherence semiconductor laser provided by the present invention has at least the following technical effects.

[0008] The mesa structure of the semiconductor laser has periodically arranged rectangular grooves, and the protruding part outside the rectangular grooves of the mesa structure forms periodic trapezoidal electrodes. The current injection electrode is a periodic trapezoidal electrode. In this way, the carrier concentration at the edge of the active region of the quantum well can be increased by applying power in sections, thereby exciting higher-order side modes and reducing the spatial coherence of the laser.

[0009] The active region of this semiconductor laser quantum well still adopts the side-emitting wide-surface Fabry-Perot (FP) resonator structure to suppress non-axial lateral mode lasing and achieve small-angle lasing.

[0010] By optimizing the edge width, period, duty cycle, and etching depth of the trapezoidal electrode, the current density difference between the current injection region and the non-current injection region of the quantum well active region is controlled within 70% while ensuring high-order side-mode lasing. This reduces the absorption loss in the non-injection region, maintains the high electro-optical conversion efficiency of the wide-area FP laser, and achieves high-efficiency continuous low-coherence output. Attached Figure Description

[0011] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0012] Figure 1 A schematic diagram of a three-dimensional structure of a trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to an embodiment of the present invention is shown.

[0013] Figure 2 The edge width of the trapezoidal electrode pattern according to an embodiment of the present invention is schematically shown. and duty cycle A schematic diagram.

[0014] Figure 3 The diagram schematically illustrates a comparison of the lateral carrier concentration distribution between a trapezoidal electrode side-emitting wide-area low-coherence semiconductor laser according to an embodiment of the present invention and a conventional side-emitting wide-area semiconductor laser.

[0015] Figure 4 The diagram schematically illustrates a far-field comparison between a trapezoidal electrode side-emitting wide-area low-coherence semiconductor laser according to an embodiment of the present invention and a conventional side-emitting wide-area semiconductor laser.

[0016] Figure reference numerals: 01—p-side electrode, 02—insulating layer, 03—p-contact layer, 04—p-confining layer, 05—p-waveguide layer, 06—quantum well active region, 07—n-waveguide layer, 08—n-confining layer, 09—substrate layer, 10—n-side electrode. Detailed Implementation

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0018] Figure 1 A schematic diagram of a three-dimensional structure of a trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to an embodiment of the present invention is shown.

[0019] like Figure 1 As shown, the base trapezoidal electrode edge-emitting wide-area low-coherence semiconductor laser in this embodiment may include a p-surface electrode 01, an insulating layer 02, a p-contact layer 03, a p-confining layer 04, a p-waveguide layer 05, a quantum well active region 06, an n-waveguide layer 07, an n-confining layer 08, a substrate layer 09, and an n-surface electrode 10.

[0020] The n-confining layer 08, n-waveguide layer 07, quantum well active region 06, p-waveguide layer 05, p-confining layer 04, p-contact layer 03, and insulating layer 02 are sequentially stacked on the first surface of the substrate.

[0021] Mesa structures are formed along the length of the semiconductor laser cavity in the p-contact layer 03 and the p-confining layer 04, with isolation trenches formed on both sides of the mesa structures. Periodically arranged rectangular grooves are formed in the mesa structures along the length of the semiconductor laser cavity. The protruding portions of the mesa structures form trapezoidal electrodes, and the areas on the insulating layer 02 corresponding to the trapezoidal electrodes form electrical contact windows. The trapezoidal electrodes are used for current injection. That is, the p-contact layer 03 and part of the p-confining layer 04 are etched only in areas other than the trapezoidal electrodes, thereby blocking current diffusion in areas other than the trapezoidal electrodes. The insulating layer 02 is etched only in the trapezoidal electrode portion, forming electrical contact windows, so ultimately only the trapezoidal electrode portion receives current injection. The isolation trenches can be formed laterally (…). Figure 1 The x-direction (as shown) provides a refractive index difference to confine the light field to the mesa structure portion, thereby improving the lateral light confinement factor of the semiconductor laser.

[0022] The P-side electrode 01 is formed on the insulating layer 02 and is connected to the trapezoidal electrode through the electrical contact window. The N-side electrode 10 forms the second surface of the substrate layer 02, with the first surface opposite to the second surface.

[0023] It should be understood that in the fabrication of a semiconductor laser, the p-contact layer 03 and the p-confining layer 04 are first etched to form an isolation trench; then, rectangular grooves arranged in a periodic pattern are etched on the mesa of the p-contact layer 03 and the p-confining layer 04 to form a trapezoidal electrode; finally, the portion of the insulating layer 2 corresponding to the trapezoidal electrode is etched away to form an electrical injection window and a p-surface electrode 01 is grown.

[0024] It should be understood that "trapezoidal" can be interpreted as the shape of a ladder.

[0025] In some embodiments, the mesa structure is perpendicular to the length of the semiconductor laser cavity and parallel to the direction of the first surface ( Figure 1 The stripe width (shown in the x-direction) is 50μm~200μm. This ensures that the semiconductor laser operates in multimode while avoiding significant heat accumulation effects due to excessively large stripe widths.

[0026] In some embodiments, the depth of the isolation groove is greater than or equal to the total thickness of the p-contact layer 03 and the p-confining layer 04. Further, the depth of the isolation groove is 1 μm to 2 μm. The isolation groove can generate a large lateral refractive index difference, effectively confining higher-order side modes.

[0027] In some embodiments, the period length of the trapezoidal electrode is 5 μm to 20 μm, such that the minimum feature structure size of the trapezoidal electrode is within the resolution range of conventional photolithography equipment.

[0028] The edge of the trapezoidal electrode has a width w that is perpendicular to the length of the semiconductor laser cavity and parallel to the direction of the first surface. eThe range is 2μm to 5μm. By localizing the carrier distribution, the gain of higher-order side modes is greater than that of lower-order side modes.

[0029] In some embodiments, during a single cycle of the trapezoidal electrode, the width of the transverse portion along the length of the semiconductor laser cavity accounts for 0.1 to 0.4 of the cycle length. This proportion of the width of the transverse portion along the length of the semiconductor laser cavity to the cycle length is the duty cycle d. c .

[0030] Figure 2 The edge width of the trapezoidal electrode pattern according to an embodiment of the present invention is schematically shown. and duty cycle A schematic diagram.

[0031] like Figure 2 As shown, duty cycle , The width of the transverse portion of the trapezoidal electrode in one cycle (which can be understood as the width of the ladder steps) is represented by T, where T is the period of the trapezoidal electrode. Adjusting the duty cycle can adjust the proportion of the non-injection region within the active region 06 of the quantum well, making the lasing intensity of higher-order side modes and lower-order side modes similar, thus achieving the best low spatial coherence output effect.

[0032] In some embodiments, the depth of the rectangular groove is greater than the thickness of the p-contact layer 03 and less than the total thickness of the p-contact layer 03 and the p-confining layer 04. That is, the portion of the p-contact layer 03 outside the trapezoidal electrode is etched through, while the portion of the p-confining layer 04 outside the trapezoidal electrode is partially etched. The depth of the rectangular groove is 0.2 μm to 1 μm, which suppresses current diffusion while avoiding the introduction of defects by the trapezoidal electrode in the active region 06 of the quantum well.

[0033] In some embodiments, the insulating layer portion corresponding to the trapezoidal electrode is etched through, and the distance between the edge of the electrical contact window and the edge of the trapezoidal electrode is greater than or equal to 0.5 μm to form the electrical contact window.

[0034] In some embodiments, the active region 06 of the quantum well is a side-emitting broad-surface Fabry-Perot resonator structure, which ensures lasing of the axial FP mode, resulting in a smaller lateral divergence angle for the laser compared to conventional chaotic microcavity lasers.

[0035] In some embodiments, the current density difference between the injected region and the non-injected region in the active region 06 of the quantum well is related to the period of the trapezoidal electrode and the depth of the rectangular groove. That is, the period and etching depth of the trapezoidal electrode should be designed together to make the current density difference between the injected region and the non-injected region less than 70%, thereby reducing the absorption loss of the non-injected region.

[0036] To more clearly illustrate the embodiments of the present invention, a specific example is given below.

[0037] In this example, the semiconductor laser has an overall width of 0.5 mm, a length of 2 mm, and a center wavelength of 940 nm. The front cavity surface coating has a reflectivity of 2%, and the rear cavity surface coating has a reflectivity greater than 99%.

[0038] The mesa structure of the semiconductor laser has a stripe width of 110 μm, with a 50 μm wide isolation trench on each side of the mesa. The mesa etching depth is 1.2 μm, which means the isolation trench depth is 1.2 μm. This provides a refractive index difference of approximately 0.005 in the lateral direction, thereby confining the light field to the mesa structure and improving the lateral light confinement factor of the semiconductor laser.

[0039] The trapezoidal electrode is etched longitudinally through p-contact layer 03 and p-confining layer 04. Figure 1 This is achieved by periodic rectangular grooves arranged in the z-direction (in the middle), with the rectangles laterally ( Figure 1 The width (in the x-direction) is 102 μm, the longitudinal width is 8 μm, and the period is 10 μm. The unetched portion of the mesa structure protrudes to form a trapezoidal electrode. The edge of the formed trapezoidal electrode... (like Figure 2 The width of the rectangular groove (as shown) is 4 μm, and the duty cycle is 0.2. The etching depth of the rectangular groove is 0.3 μm. This removes the p-contact layer 03, suppressing lateral current diffusion. On the other hand, the shallow etching of 0.3 μm leaves some space for current diffusion, so that the current density in the non-injection region of the quantum well active region 06 is more than 30% of the current density in the injection region. Its carrier concentration is higher than the threshold carrier concentration, thus avoiding the absorption loss introduced by the non-injection region.

[0040] The insulating layer 02 is made of SiO2 and has a thickness of approximately 200 nm. An electrical injection window is generated by etching the mesa trapezoidal electrode portion of the insulating layer 02. The distance between the edge of the window and the edge of the trapezoidal structure of the contact layer is 0.5 μm, which effectively isolates the portion outside the trapezoidal electrode.

[0041] The p-side electrode 01 is made of Ti / Pt / Au, and the n-side electrode 10 is made of Au / Ge / Ni. The p-side electrode 01 forms a good ohmic contact with the p-contact layer 03 at the electrical injection window.

[0042] The p-confinement layer 04, p-waveguide layer 05, n-waveguide layer 07, and n-confinement layer 08 are all made of AlGaAs. The Al composition and doping concentration of the materials are designed based on the principles of optical waveguides and electrical contact requirements. The p-contact layer 03 and the substrate layer 09 are both made of GaAs with a high doping concentration. The active region of the quantum well, the 06 well layer, is made of InGaAs, and the barrier layer is made of AlGaAs; neither layer is doped. A composition-gradient layer is grown between the different layers to reduce the defect density.

[0043] Figure 3 The diagram schematically illustrates a comparison of the lateral carrier concentration distribution between a trapezoidal electrode side-emitting wide-area low-coherence semiconductor laser according to an embodiment of the present invention and a conventional side-emitting wide-area semiconductor laser.

[0044] like Figure 3 As shown in the figure, the numerical simulation results show that the trapezoidal electrode edge-emitting wide-area low-coherence semiconductor laser provided in this example can significantly improve the carrier concentration at the edge of the mesa structure.

[0045] Figure 4 The diagram schematically illustrates a far-field comparison between a trapezoidal electrode side-emitting wide-area low-coherence semiconductor laser according to an embodiment of the present invention and a conventional side-emitting wide-area semiconductor laser.

[0046] like Figure 4 As shown, the trapezoidal electrode side-emitting wide-area low-coherence semiconductor laser provided in this example has a larger lateral divergence angle, indicating an increase in the equivalent number of side modes and thus a decrease in spatial coherence. Due to the use of a FP resonator, there are no non-axial chaotic modes within the laser cavity. This ensures the absence of large-angle sidelobes in the far field, preserving the high directivity of the laser, and controlling the overall lateral divergence angle to within 30°. Furthermore, the ridge waveguide structure formed by the mesa structure avoids sidewall losses caused by etching curved surfaces in chaotic microcavity lasers, thus preserving the high electro-optical conversion efficiency of the side-emitting wide-area laser. Conventional low-coherence semiconductor lasers have waveguide characteristic widths of 300 μm to 500 μm, leading to severe heat accumulation, which can only be mitigated through pulsed lasing. In this embodiment, the laser stripe width is only 110 μm, enabling high-power continuous lasing.

[0047] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A trapezoidal electrode-based edge-emitting wide-area low-coherence semiconductor laser, characterized in that, include: Substrate layer; An n-confinement layer, an n-waveguide layer, a quantum well active region, a p-waveguide layer, a p-confinement layer, a p-contact layer, and an insulating layer are sequentially stacked on the first surface of the substrate layer. The p-contact layer and the p-confinement layer form mesa structures along the length of the semiconductor laser cavity. Isolation grooves are formed on both sides of the mesa structures. Periodically arranged rectangular grooves are formed in the mesa structures along the length of the semiconductor laser cavity. The protruding portions of the mesa structures form trapezoidal electrodes. An electrical contact window is formed in the region corresponding to the trapezoidal electrodes on the insulating layer. The trapezoidal electrodes are used for current injection. The P-side electrode is formed on the insulating layer and connects to the trapezoidal electrode through the electrical contact window; The N-side electrode forms the second surface of the substrate layer, with the first surface opposite to the second surface.

2. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1, characterized in that, The width of the mesa structure along the direction perpendicular to the length of the semiconductor laser cavity and parallel to the first surface is 50μm~200μm.

3. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1, characterized in that, The depth of the isolation groove is greater than or equal to the total thickness of the p contact layer and the p restriction layer.

4. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 3, characterized in that, The depth of the isolation groove is 1μm~2μm.

5. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1, characterized in that, The period length of the trapezoidal electrode is 5μm to 20μm, and the width of the edge of the trapezoidal electrode along the direction perpendicular to the length of the semiconductor laser cavity and parallel to the first surface is 2μm to 5μm.

6. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1 or 5, characterized in that, In a single cycle of the trapezoidal electrode, the width of the transverse portion along the length of the semiconductor laser cavity accounts for 0.1 to 0.4 of the cycle length.

7. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1, characterized in that, The depth of the rectangular groove is greater than the thickness of the p-contact layer and less than the total thickness of the p-contact layer and the p-restriction layer. The depth of the rectangular groove is 0.2 μm to 1 μm.

8. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1, characterized in that, The distance between the edge of the electrical contact window and the edge of the trapezoidal electrode is greater than or equal to 0.5 μm.

9. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1, characterized in that, The active region of the quantum well is a side-emitting broad-faceted Fabry-Perot resonator structure.

10. The trapezoidal electrode-side-emitting wide-area low-coherence semiconductor laser according to claim 1 or 9, characterized in that, The current density difference between the injected and non-injected regions in the active region of the quantum well is related to the period of the trapezoidal electrode and the depth of the rectangular groove, and the current density difference between the injected and non-injected regions is less than 70%.

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