A semiconductor laser with switchable spectral width and its fabrication method

Abstract

This invention relates to the field of semiconductor laser technology, and more particularly to a semiconductor laser with switchable spectral width. The laser includes a mesa and a ridge waveguide located in the middle of the mesa. From bottom to top, the mesa includes an N-type electrode layer, a substrate layer, an N-type cladding layer, an N-type waveguide layer, an active layer, and a P-type waveguide layer. The ridge waveguide is located at the upper middle part of the P-type waveguide layer and, from bottom to top, includes a P-type cladding layer, a P-type capping layer, and a P-type electrode. The two sides of the ridge waveguide are insulating layers, and a periodic electrode is included on the insulating layer on one side of the ridge waveguide. When a current is applied to the periodic electrode, frequency selectivity can be achieved by modulating the optical field distributed within the periodic electrode region, thus narrowing the laser spectral width. When no current is applied to the periodic electrode, the laser oscillates at the front and rear cavity surfaces and exhibits broadband lasing characteristics. This invention also provides a method for fabricating a semiconductor laser with switchable spectral width.

Description

Technical Field

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

[0002] Semiconductor lasers have many advantages, such as light weight, small size, low power consumption, easy integration, and high power and high efficiency output. Currently, semiconductor lasers are widely used in materials processing, laser communication, laser pumping, laser sensing, military, medical and other fields.

[0003] Depending on the application scenario, the performance parameters of semiconductor lasers vary greatly. Traditional applications such as laser pumping, illumination, and power transfer require high output power from semiconductor lasers, which are often wide-strip (100-200µm) FP cavity structures with a relatively large spectral width (1-3nm). In contrast, applications such as laser communication and laser sensing require narrow linewidth characteristics, and the semiconductor lasers used are often narrow-strip (<5µm) lasers with DFB or DBR gratings. The output laser is typically single-frequency, with a spectral width generally less than 0.1nm, but the output power is reduced by more than an order of magnitude compared to wide-strip lasers. Existing semiconductor lasers mainly suffer from the following problems:

[0004] 1. Existing semiconductor lasers can usually only achieve either wide-spectrum high power or single-frequency low noise. Semiconductor lasers that aim to achieve both low noise and high power are mainly made by adding a tapered optical amplification section after a narrow-strip laser based on DFB or DBR gratings. This method can effectively improve the output power to a certain extent, but due to the frequency selection introduced by the grating, its output power still cannot be compared with traditional wide-strip lasers, and it cannot achieve the flexible selection of high-power wide-spectrum and single-frequency narrow-spectrum lasers.

[0005] 2. Currently, an increasing number of emerging applications are placing new demands on the performance parameters of semiconductor lasers. For example, in new wireless laser charging applications, the transmitter is integrated into an indoor ceiling light fixture, and the laser is transmitted simultaneously between the transmitter and multiple receiving terminals (such as multiple mobile phones) to charge the terminals. The higher the laser power, the faster the charging efficiency. More novel applications require simultaneous information transmission during wireless charging. This requirement necessitates that laser communication applications have narrow linewidth characteristics. However, existing standalone semiconductor lasers cannot flexibly switch between high-power broadband and single-frequency narrow spectrum, and therefore cannot meet the needs of future emerging applications such as wireless laser charging.

[0006] In conclusion, how to design and manufacture a semiconductor laser with switchable spectral width is an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a semiconductor laser with switchable spectral width and its fabrication method. By extending a portion of the light beyond a ridge waveguide and integrating a periodic electrode structure in this region, the spectral width of the laser can be switched by controlling the periodic electrodes. This allows for flexible selection between high-power broadband and single-frequency narrow-spectrum lasers, meeting the performance requirements of an increasing number of emerging applications for semiconductor lasers.

[0008] To achieve the above objectives, the present invention proposes the following technical solution: a semiconductor laser with switchable spectral width, the laser comprising a mesa and a ridge waveguide located in the middle of the mesa, the two sides of the ridge waveguide being insulating layers, and a periodic electrode being included on the insulating layer on one side of the ridge waveguide; the periodic electrode is formed by etching the insulating layer and depositing patterned electrodes on the laser surface; when a current is applied to the periodic electrode, a periodic carrier distribution can be formed, and the refractive index of the periodic electrode region exhibits a periodic distribution, frequency selectivity is achieved by modulating the light field distributed in the periodic electrode region, and the laser spectral width is narrowed; when no current is applied to the periodic electrode, the laser oscillates through the front and rear cavity surfaces and has broadband lasing characteristics.

[0009] Preferably, the period of the periodic electrode is 2 micrometers to 20 micrometers; the duty cycle of the periodic electrode is 1% to 80%; and the area of ​​the periodic electrode is 0.5 to 5 square micrometers.

[0010] Preferably, the mesa includes, from bottom to top, an N-type electrode layer, a substrate layer, an N-type cladding layer, an N-type waveguide layer, an active layer, and a P-type waveguide layer; the ridge waveguide is located at the upper middle part of the P-type waveguide layer, and the insulating layer is located at the upper part of the P-type waveguide layer and on both sides of the ridge waveguide; one side of the P-type waveguide layer is formed by etching the insulating layer to form a periodic electrode.

[0011] Preferably, the ridge waveguide comprises, from bottom to top, a P-type cladding, a P-type capping layer, and a P-type electrode.

[0012] Preferably, the substrate is an N-type GaAs material; the N-type cladding is an AlGaAs material; the N-type waveguide layer is an AlGaAs material; the active layer is a barrier / quantum well / barrier structure, and the active layer material is AlGaAsP / InAlGaAs / AlGaAsP; the P-type waveguide layer is an AlGaAs material.

[0013] Preferably, the N-type cladding has an Al composition of 0.1-0.6, a thickness of 0.5 μm-3 μm, and is doped with Si at a doping concentration of 1E18-8E18 / cm3; the N-type waveguide layer has an Al composition of 0.05-0.7, a thickness of 0.1 μm-10 μm, and is doped with Si at a doping concentration of 1E16-8E18 / cm3; the active layer has an In composition of 0-0.5, an Al composition of 0-0.5, a P composition of 0-0.2, a barrier thickness of 1 nm-200 nm, a quantum well thickness of 1 nm-20 nm, and an emission wavelength of 700 nm-1200 nm; the P-type waveguide layer has an Al composition of 0.05-0.7, a thickness of 0.1 μm-10 μm, and is doped with C at a doping concentration of 1E16-8E18 / cm3.

[0014] Preferably, the P-type cladding is made of AlGaAs material, with an Al composition of 0.1-0.6, a thickness of 0.5 μm-3 μm, and C as the dopant with a doping concentration of 1E18-8E18 / cm3; the P-type capping layer is made of GaAs material, with a thickness of 0.1 μm-3 μm, and C as the dopant with a doping concentration of 1E18-1E20 / cm3.

[0015] Preferably, the thickness of the periodic electrode and the P-type electrode is 200 nm to 500 nm, and the material of the periodic electrode and the P-type electrode is an alloy material including titanium, platinum, gold, nickel and germanium.

[0016] Preferably, the insulating layer is made of SiO2 or Si3N4, and the thickness of the insulating layer is 50 nanometers to 1000 nanometers.

[0017] A method for fabricating a semiconductor laser with switchable spectral width, comprising the following steps:

[0018] S1: Take a GaAs wafer and sequentially prepare an N-type cladding, an N-type waveguide layer, an active layer, a P-type waveguide layer, a P-type cladding, and a P-type capping layer through epitaxial growth to obtain a wafer with an epitaxial structure.

[0019] S2: Ridge waveguides are fabricated on the surface of the grown wafer using photolithography and dry etching processes, followed by mask removal and cleaning processes to obtain wafers containing ridge waveguides.

[0020] S3: Deposit insulating layer material on the surface of a wafer containing a ridge waveguide, and fabricate patterned electrode injection windows and periodic electrode windows on the surface of the insulating layer using photolithography and dry etching processes;

[0021] S4: Perform a third photolithography process on the wafer surface and prepare a lift-off mask pattern;

[0022] S5: Grow a P-type electrode in a metal film evaporation equipment, perform a lift-off process, and prepare a P-type electrode and a periodic electrode;

[0023] S6: Thin, polish, and clean the N-type substrate, sputter an N-type electrode layer on the N-type substrate, and perform an annealing process on the wafer to form a European-style contact.

[0024] S7: The wafer is cleaved into bars, and the bars are cleaved into chips.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention, based on a traditional wide-strip FP-cavity semiconductor laser, modifies the lateral distribution of the optical field to extend part of the light beyond the ridge waveguide. A periodic electrode structure is integrated in this region. When current is applied to the electrodes, a periodic carrier distribution is formed. Since the refractive index of the semiconductor material is related to the carrier distribution, the refractive index in this region exhibits a periodic distribution, modulating the optical field distributed in this region to achieve frequency selectivity and narrow the laser spectral width. When no current is applied to the periodic electrodes, there is no periodic carrier and refractive index distribution in this region, and the frequency selectivity is lost. The laser relies on front and rear cavity surface oscillations, exhibiting broadband lasing characteristics. By controlling the periodic electrodes, the spectral width of the semiconductor laser can be switched.

[0027] 2. In this invention, the spectral width of a single laser chip can be controlled by an electrode switch, enabling free switching of spectral width within a single device. Compared to existing technologies that require at least two laser structures to achieve spectral width switching, with completely independent optical paths and beam shaping systems for each laser, this solution requires only one laser chip to achieve free spectral width switching, and only one optical path and beam shaping system is needed, simplifying the system and reducing costs. Attached Figure Description

[0028] Figure 1 This is a three-dimensional structural diagram of a semiconductor laser provided in an embodiment of the present invention.

[0029] Figure 2 This is a top view of the semiconductor laser provided in an embodiment of the present invention.

[0030] Figure 3 This is a cross-sectional view of a semiconductor laser provided in an embodiment of the present invention along the direction of the periodic electrode distribution.

[0031] Figure 4 This is a schematic diagram of the internal carrier distribution of the device caused by the periodic electrodes provided in an embodiment of the present invention.

[0032] Figure 5This is a schematic diagram of the internal optical field distribution of the device caused by the periodic electrodes provided in an embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram of the optical loss spectrum caused by the periodic electrode provided in an embodiment of the present invention.

[0034] Figure reference numerals: 1. N-type electrode layer, 2. substrate layer, 3. N-type cladding, 4. N-type waveguide layer, 5. active layer, 6. P-type waveguide layer, 7. P-type cladding, 8. P-type capping layer, 9. P-type electrode, 10. periodic electrode, 11. insulating layer, 12. ridge waveguide, 13. mesa. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1-6 The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and do not constitute a limitation thereof.

[0036] A semiconductor laser with switchable spectral width, such as Figure 1 As shown, the laser includes a mesa 13 and a ridge waveguide 12 located in the middle of the mesa 13. The two sides of the ridge waveguide 12 are insulating layers 11, and a periodic electrode 10 is included on the insulating layer 11 on one side of the ridge waveguide 12. The periodic electrode 10 is formed by etching the insulating layer 11 and depositing patterned electrodes on the laser surface. The period of the periodic electrode 10 is 2 micrometers to 20 micrometers. The duty cycle of the periodic electrode 10 is 1% to 80%. The area of ​​the periodic electrode 10 is 0.5 to 5 square micrometers. The shape of the periodic electrode 10 is preferably square, rectangular, circular, elliptical or rhomboid. Those skilled in the art can also set the periodic electrode 10 to other shapes according to actual needs. The periodic electrode 10 is prepared by photolithography.

[0037] Figure 1 The arrow at point M indicates the laser's output direction, and the transverse direction of the laser is perpendicular to the output direction. By changing the transverse distribution of the light field, part of the light is extended beyond the ridge waveguide, and a periodic electrode structure is integrated in this region to achieve switchable spectral width. When a current is applied to the periodic electrode 10, a periodic carrier distribution is formed, resulting in a periodic refractive index distribution in the region of the periodic electrode 10. By modulating the light field distributed in the region of the periodic electrode 10, frequency selectivity is achieved, and the laser spectral width is narrowed. The periodic current distribution is as follows: Figure 3 As shown by the S-line in the figure; when no current is applied to the periodic electrode 10, the laser oscillates through the front and rear cavity surfaces and has broadband lasing characteristics.

[0038] Among them, through Figure 4The periodic distribution of the electrodes can be observed from the carrier distribution inside the device; the periodic refractive index introduced by the periodic electrode 10 is calculated through simulation. Figure 5 The optical field distribution inside the device shown illustrates the modulation effect of the periodic refractive index on the optical field; through... Figure 5 The calculated results show the loss modulation effect of the periodic refractive index structure on the optical field, as follows: Figure 6 As shown, taking the 885nm wavelength selected in the calculation process as a special case, other wavelengths can be achieved simply by designing the periodic parameters of the periodic electrode 10. It can be seen that the periodic electrode 10 introduces a loss spectrum at 885nm, with a spectral half-width of only 0.6nm, indicating that the periodic electrode 10 has selective characteristics for specific frequencies of the spectrum, thereby narrowing the spectral width.

[0039] like Figure 2 As shown, the mesa 13 includes, from bottom to top, an N-type electrode layer 1, a substrate layer 2, an N-type cladding layer 3, an N-type waveguide layer 4, an active layer 5, and a P-type waveguide layer 6; a ridge waveguide 12 is located at the upper middle part of the P-type waveguide layer 6, and an insulating layer 11 is located at the upper end of the P-type waveguide layer 6 and on both sides of the ridge waveguide 12; a periodic electrode 10 is formed on one side of the P-type waveguide layer 6 by etching the insulating layer 11; the ridge waveguide 12 includes, from bottom to top, a P-type cladding layer 7, a P-type capping layer 8, and a P-type electrode 9.

[0040] Substrate 2 is made of N-type GaAs; N-type cladding 3 is made of AlGaAs with an Al composition of 0.1-0.6, a thickness of 0.5-3 μm, and Si as the dopant with a doping concentration of 1E18-8E18 / cm3; N-type waveguide 4 is made of AlGaAs with an Al composition of 0.05-0.7, a thickness of 0.1-10 μm, and Si as the dopant with a doping concentration of 1E16-8E18 / cm3; active layer 5 is a barrier / quantum well / barrier structure, made of AlGaAsP / InAlGaAs / AlGaAsP with an In composition of 0-0.5, an Al composition of 0-0.5, and a P composition of 0-0. 2. The barrier thickness is 1 nm to 200 nm, the quantum well thickness is 1 nm to 20 nm, and the emission wavelength is 700 nm to 1200 nm; the P-type waveguide layer 6 is made of AlGaAs material, with an Al composition of 0.05-0.7, a thickness of 0.1 μm to 10 μm, and C as the dopant with a doping concentration of 1E16-8E18 / cm3; the P-type cladding layer 7 is made of AlGaAs material, with an Al composition of 0.1-0.6, a thickness of 0.5 μm to 3 μm, and C as the dopant with a doping concentration of 1E18-8E18 / cm3; the P-type capping layer 8 is made of GaAs material, with a thickness of 0.1 μm to 3 μm, C as the dopant with a doping concentration of 1E18-1E20 / cm3.

[0041] The periodic electrode 10 and the P-type electrode 9 have a thickness of 200 nm to 500 nm, and the materials of the periodic electrode 10 and the P-type electrode 9 are alloy materials including titanium, platinum, gold, nickel and germanium; the insulating layer 11 is made of SiO2 or Si3N4, and the thickness of the insulating layer 11 is 50 nm to 1000 nm.

[0042] It is worth noting that the laser materials and structures in the 700-1200nm waveguide range of this scheme use GaAs system. If the material system is changed to InP system, a laser in the 1200-1600nm band range can be realized. The epitaxial structure used is the mature InP-based semiconductor laser structure, and the device structure and design method are the same.

[0043] A method for fabricating a semiconductor laser with switchable spectral width, comprising the following steps:

[0044] S1: Take a GaAs wafer and sequentially prepare an N-type cladding layer 3, an N-type waveguide layer 4, an active layer 5, a P-type waveguide layer 6, a P-type cladding layer 7, and a P-type capping layer 8 through epitaxial growth to obtain a wafer containing an epitaxial structure.

[0045] S2: Ridge waveguides are fabricated on the surface of the grown wafer using photolithography and dry etching processes, followed by mask removal and cleaning processes to obtain wafers containing ridge waveguides.

[0046] S3: An insulating layer 11 material is deposited on the surface of a wafer containing a ridge waveguide, and patterned electrode injection windows and periodic electrode 10 windows are fabricated on the surface of the insulating layer 11 using photolithography and dry etching processes.

[0047] S4: Perform a third photolithography process on the wafer surface and prepare a lift-off mask pattern;

[0048] S5: Grow a P-type electrode 9 in a metal film evaporation equipment, perform a lift-off process, and prepare the P-type electrode 9 and the periodic electrode 10.

[0049] S6: Thin, polish and clean the N-type substrate, sputter N-type electrode layer 1 on the N-type substrate, and perform annealing process on the wafer to form Euro-type contact;

[0050] S7: The wafer is cleaved into bars, and the bars are cleaved into chips.

[0051] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0052] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A semiconductor laser with switchable spectral width, characterized in that, The laser includes a mesa (13) and a ridge waveguide (12) located in the middle of the mesa (13). The two sides of the ridge waveguide (12) are insulating layers (11), and the insulating layer (11) on one side of the ridge waveguide (12) includes a periodic electrode (10). The periodic electrode (10) is formed by etching the insulating layer (11) and depositing a patterned electrode on the surface of the laser. When a current is applied to the periodic electrode (10), a periodic carrier distribution can be formed, and the refractive index of the periodic electrode (10) region can be periodically distributed. Frequency selection is formed by modulating the light field distributed in the periodic electrode (10) region, and the laser spectrum is narrowed. When no current is applied to the periodic electrode (10), the laser oscillates through the front and rear cavity surfaces and has broadband lasing characteristics. The mesa (13) includes, from bottom to top, an N-type electrode layer (1), a substrate layer (2), an N-type cladding layer (3), an N-type waveguide layer (4), an active layer (5), and a P-type waveguide layer (6); a ridge waveguide (12) is located at the upper middle part of the P-type waveguide layer (6), and an insulating layer (11) is located at the upper part of the P-type waveguide layer (6) and on both sides of the ridge waveguide (12); a periodic electrode (10) is formed on one side of the P-type waveguide layer (6) by etching the insulating layer (11). The ridge waveguide (12) includes, from bottom to top, a P-type cladding (7), a P-type capping layer (8), and a P-type electrode (9).

2. The semiconductor laser with switchable spectral width according to claim 1, characterized in that, The periodic electrode (10) has a period of 2 micrometers to 20 micrometers; the duty cycle of the periodic electrode (10) is 1% to 80%; and the area of ​​the periodic electrode (10) is 0.5 to 5 square micrometers.

3. The semiconductor laser with switchable spectral width according to claim 1, characterized in that, The substrate layer (2) is made of N-type GaAs material; the N-type cladding layer (3) is made of AlGaAs material; the N-type waveguide layer (4) is made of AlGaAs material; the active layer (5) is a barrier / quantum well / barrier structure, and the active layer (5) is made of AlGaAsP / InAlGaAs / AlGaAsP material. The P-type waveguide layer (6) is made of AlGaAs material.

4. The semiconductor laser with switchable spectral width according to claim 3, characterized in that, The N-type cladding (3) has an Al composition of 0.1-0.6, a thickness of 0.5-3 μm, and is doped with Si at a concentration of 1E18-8E18 / cm3; the N-type waveguide layer (4) has an Al composition of 0.05-0.7, a thickness of 0.1-10 μm, and is doped with Si at a concentration of 1E16-8E18 / cm3; the active layer (5) has an In composition of 0-0.5, an Al composition of 0-0.5, a P composition of 0-0.2, a barrier thickness of 1-200 nm, a quantum well thickness of 1-20 nm, and a light emission band of 700-1200 nm; the P-type waveguide layer (6) has an Al composition of 0.05-0.7, a thickness of 0.1-10 μm, and is doped with C at a concentration of 1E16-8E18 / cm3.

5. The semiconductor laser with switchable spectral width according to claim 4, characterized in that, The P-type cladding (7) is made of AlGaAs material, with an Al composition of 0.1-0.6, a thickness of 0.5-3 micrometers, and C as the dopant with a doping concentration of 1E18-8E18 / cm3; the P-type capping layer (8) is made of GaAs material, with a thickness of 0.1-3 micrometers, and C as the dopant with a doping concentration of 1E18-1E20 / cm3.

6. The semiconductor laser with switchable spectral width according to claim 5, characterized in that, The thickness of the periodic electrode (10) and the P-type electrode (9) is 200-500 nanometers, and the materials of the periodic electrode (10) and the P-type electrode (9) are alloy materials including titanium, platinum, gold, nickel and germanium.

7. The semiconductor laser with switchable spectral width according to claim 6, characterized in that, The insulating layer (11) is made of SiO2 or Si3N4 and has a thickness of 50 nanometers to 1000 nanometers.

8. A method for fabricating a semiconductor laser with switchable spectral width, for fabricating the semiconductor laser according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Take a GaAs wafer and sequentially prepare an N-type cladding (3), an N-type waveguide layer (4), an active layer (5), a P-type waveguide layer (6), a P-type cladding (7), and a P-type capping layer (8) through epitaxial growth to obtain a wafer containing an epitaxial structure; S2: Ridge waveguides are fabricated on the surface of the grown wafer using photolithography and dry etching processes, followed by mask removal and cleaning processes to obtain wafers containing ridge waveguides. S3: Deposit insulating layer (11) material on the surface of a wafer containing a ridge waveguide, and use photolithography and dry etching processes to prepare patterned electrode injection windows and periodic electrode (10) windows on the surface of the insulating layer (11); S4: Perform a third photolithography process on the wafer surface and prepare a lift-off mask pattern; S5: Grow a P-type electrode (9) in a metal film evaporation equipment, perform a lift-off process, and prepare a P-type electrode (9) and a periodic electrode (10). S6: Thin, polish and clean the N-type substrate, sputter an N-type electrode layer (1) on the N-type substrate, and perform an annealing process on the wafer to form a European-type contact; S7: The wafer is cleaved into bars, and the bars are cleaved into chips.

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