Vertical dislocation bichiral cavity two-dimensional photonic crystal semiconductor laser and preparation method thereof

Abstract

The application discloses a vertical dislocation two-dimensional photonic crystal semiconductor laser with two chiral cavities and a preparation method thereof. The vertical dislocation two-dimensional photonic crystal semiconductor laser comprises, from bottom to top, a semiconductor substrate, an n-type cladding layer, an n-type mirror, a first chiral photonic crystal cavity, a first regrowth buffer layer, a light-emitting active region, a second chiral photonic crystal cavity, a second regrowth buffer layer, a p-type cladding layer, a current expansion layer and a current injection layer. The two chiral photonic crystal cavities are arranged at different vertical positions, and the chiral units in the two chiral photonic crystal cavities have a relative displacement in a plane. The relative displacement includes a rotation angle or a relative translation amount. Meanwhile, the in-plane mirror symmetry and the vertical inversion symmetry are broken, a three-dimensional non-mirror symmetry structure is formed, the radiation loss difference between left-handed circular polarization and right-handed circular polarization modes, the mode threshold difference and the near-field chirality density difference are enhanced, and thus circular polarization output, polarization locking, low threshold mode selection, far-field directivity enhancement and large-area laser mode field regulation are realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to a vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser and its fabrication method. Background Technology

[0002] Semiconductor lasers, with their advantages of high electro-optic efficiency, small size, fast modulation speed, ease of on-chip integration, and mass production, have become core devices in modern optoelectronic systems. However, with the development of monolithic integration technology, on-chip optical field manipulation, quantum photonics, and chiral optics, traditional semiconductor lasers that directly output linearly polarized light are no longer sufficient to meet the urgent needs of quantum communication, polarization-multiplexed communication, chiral biodetection, and novel display technologies. Therefore, how to directly achieve stable circularly polarized lasing output within a semiconductor laser has become an important research direction for semiconductor optoelectronic devices.

[0003] Two-dimensional photonic crystal semiconductor lasers (PCSELs) can provide high Q values ​​and strong mode confinement through band-edge modes, guided-mode resonant modes, or quasi-continuous bound-state modes, and form out-of-plane radiation output through Bragg coupling. They offer advantages in large-area single-mode operation, high directionality, low divergence angle, and polarization control. By optimizing the cell shape, fill factor, lattice constant, and symmetry of the photonic crystal, the frequency, quality factor, radiation loss, and far-field polarization state of the laser mode can be tuned. On the other hand, chiral optical structures are an important means of achieving circular polarization control, capable of producing different optical responses for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP). In recent years, planar chiral nanostructures, chiral metasurfaces, and chiral photonic crystal plates have been used to generate significant circular dichroism, circular polarization selectivity, and enhanced optical chirality density. By reducing the in-plane symmetry of the photonic crystal plate, a strong difference in left-handed and right-handed circular polarization responses can be obtained, enabling TE or TM modes to form strongly chiral quasi-continuous bound states and achieving circular dichroism (CD) close to 1.

[0004] However, most existing chiral structures are still limited to single-layer, two-dimensional, passive designs. Their main drawbacks include: most existing chiral photonic crystals or chiral metasurfaces are passive structures, mainly focusing on the differences in transmission, reflection, or absorption of external incident light, without directly introducing the chiral optical response into the active cavity mode competition process of semiconductor lasers; existing two-dimensional chiral photonic crystal structures are usually single-layer structures, introducing chirality by breaking the in-plane mirror symmetry, resulting in limited differences in radiation loss, quality factor, and threshold gain between left-handed and right-handed circularly polarized modes; in single-layer chiral photonic crystal plates, although aperture shape, rotation angle, fill factor, and etching depth are adjustable, it is often difficult to simultaneously satisfy high Q, strong chiral response, low threshold, and high directional output; for semiconductor lasers, to achieve stable circularly polarized output, the key is not only to make the photonic crystal plate structure have different transmittances for the two circular polarizations, but also to make the two circularly polarized modes exhibit different mode losses, Q values, threshold gains, and even different near-field optical chirality densities and different radiation directions within the laser cavity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a vertically misaligned bichiral cavity two-dimensional photonic crystal semiconductor laser structure and fabrication method. By setting a first chiral photonic crystal cavity and a second chiral photonic crystal cavity in a two-dimensional photonic crystal semiconductor laser, and ensuring that the two cavities have a non-zero vertical spacing and relative rotation and / or relative translation in planar projection, a vertically misaligned bichiral photonic crystal resonator is formed. This bichiral resonator is coupled to the same laser resonant mode, enabling the left and right circular polarization modes to obtain different radiation losses or different threshold gains. This solves the problems of insufficient circular polarization mode selection capability of existing single-layer chiral structures, the difficulty of directly using passive structures in electrically pumped lasers, and the limited circular polarization stability of laser output.

[0006] This invention discloses a vertically misaligned bipolar two-dimensional photonic crystal semiconductor laser, comprising, from bottom to top, a semiconductor substrate, an n-type cladding, an n-type mirror, a first chiral photonic crystal cavity, a first regeneration buffer layer, a light-emitting active region, a second chiral photonic crystal cavity, a second regeneration buffer layer, a p-type cladding, a current spreading layer, and a current injection layer; a p-plane electrode is formed on the upper surface of the current injection layer, and an n-plane electrode is formed on the lower surface of the semiconductor substrate to form a metal electrode structure; The first chiral photonic crystal cavity and the second chiral photonic crystal cavity together form a vertically misaligned bichiral photonic crystal resonant cavity. The first chiral unit in the first chiral photonic crystal cavity and the second chiral unit in the second chiral photonic crystal cavity have relative displacement in the plane, and there is a non-zero vertical spacing between the two layers to form a bichiral non-mirror symmetrical resonant structure. This allows the first chiral photonic crystal cavity and the second chiral photonic crystal cavity to be coupled to the same laser resonant mode, and the left-hand circular polarization mode and the right-hand circular polarization mode to have different radiation losses or different threshold gains. The relative displacement includes at least one of relative rotation and relative translation.

[0007] Furthermore, the first chiral unit and the second chiral unit are one or more combinations of chiral structures such as L-shaped holes, S-shaped holes, C-shaped holes, windmill-shaped holes, and eccentric elliptical holes; the filling material in the hole may be air, chiral materials, III-V compound semiconductor materials, or combinations thereof.

[0008] Furthermore, the relative rotation angle between the first chiral unit and the second chiral unit is 0°-90°, preferably 10°-40°.

[0009] Furthermore, the relative translation amounts of the first chiral unit and the second chiral unit are 0.01a1 to 0.50a1 or 0.01a2 to 0.50a2 in the x and y directions, respectively. Wherein, a1 is the lattice constant of the first chiral photonic crystal cavity, and a2 is the lattice constant of the second chiral photonic crystal cavity.

[0010] Furthermore, the etching depths of the first chiral unit and the second chiral unit are different, forming an asymmetric effective refractive index modulation and an asymmetric radiation coupling channel.

[0011] Furthermore, the first chiral photonic crystal cavity and the second chiral photonic crystal cavity have the same lattice constant or different lattice constants, forming a resonant coupled cavity structure.

[0012] Furthermore, the vertical spacing between the first chiral photonic crystal cavity and the second chiral photonic crystal cavity is 10 nm-1000 nm, preferably 100 nm-500 nm.

[0013] Furthermore, the material systems of the first chiral photonic crystal cavity and the second chiral photonic crystal cavity can be one of the semiconductor material systems of GaAs, InP, InGaAsP, GaInP, GaN, InGaN, AlGaN, and GaSb, respectively.

[0014] Furthermore, the first chiral photonic crystal cavity is located in the near-field high-field region vertically below the light-emitting active region, and the second chiral photonic crystal cavity is located in the near-field high-field region vertically above the light-emitting active region, or the first chiral photonic crystal cavity and the second chiral photonic crystal cavity are both located on the same side of the light-emitting active region but at different etching depths.

[0015] Furthermore, the vertically misaligned bipolar photonic crystal resonator is used to support one or more of the following: band-edge mode, quasi-continuous bound state mode, and guided mode resonance mode. The radiation loss of the left-hand circularly polarized mode and the right-hand circularly polarized mode are different.

[0016] Furthermore, the light-emitting active region can be any one of a single quantum well, multiple quantum wells, quantum dot, or quantum cascade active region.

[0017] Furthermore, the semiconductor material system is InGaN / GaN, GaAs / AlGaAs, InGaAs / GaAs, InP / InGaAsP, InP / InAlGaAs, GaSb / AlGaSb, InAs / GaSb, or a terahertz quantum cascade semiconductor material system.

[0018] Furthermore, the metal electrode structure includes a p-type metal electrode and an n-type metal electrode, wherein the p-type metal electrode is a ring electrode, a mesh electrode, or a transparent conductive electrode; and the n-type metal electrode is a mode-matching electrode.

[0019] Furthermore, the vertically misaligned bipolar photonic crystal resonator makes the quality factor difference between the left-hand circular polarization mode and the right-hand circular polarization mode greater than 5%.

[0020] Furthermore, the vertically misaligned bipolar photonic crystal resonator enables the circular polarization degree of the output chiral laser to be better than 0.6.

[0021] Furthermore, the first regrowth buffer layer and the second regrowth buffer layer respectively fill the first chiral unit and the second chiral unit, with a filling ratio greater than 0, thereby reducing the roughness of the sidewalls of the first chiral unit and the second chiral unit and improving the consistency of interlayer coupling.

[0022] Furthermore, the thicknesses of the first regrowth buffer layer and the second regrowth buffer layer are set to 10 nm-100 nm.

[0023] The present invention also provides a method for fabricating the above-mentioned photonic crystal semiconductor laser, comprising the following steps: Step 1: Provide a semiconductor substrate and sequentially epitaxially grow an n-type cladding layer and an n-type mirror; Step 2: Extend the first chiral photonic crystal cavity at the first vertical position; Step 3: Fabricate a first chiral unit on the first chiral photonic crystal cavity, and then epitaxially grow a first regeneration buffer layer; Step 4: Continue epitaxial growth of the active light-emitting region; Step 5: Extend a second chiral photonic crystal cavity at the second vertical position; Step 6: Fabricate a second chiral unit with a preset rotation angle or translational displacement relative to the first chiral unit on the second chiral photonic crystal cavity; Step 7: Then, sequentially epitaxially grow a second regrowth buffer layer, a p-type cladding layer, a current spreading layer, and a current injection layer; Step 8: Prepare the metal electrode structure; Step 9: Complete the laser chip fabrication, annealing, passivation, cleaving, and packaging.

[0024] Furthermore, the chiral units in steps 3 and 6 are prepared using one or more of the following methods: ultraviolet lithography, electron beam lithography, nanoimprinting, and laser direct writing.

[0025] Furthermore, the regrowth buffer layer in steps 3 and 7 is prepared by molecular beam epitaxy or metal-organic chemical vapor deposition; or by atomic layer deposition to form a dielectric passivation / filling layer.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention directly integrates the chiral optical response into the active cavity of a semiconductor laser, utilizing a laser mode competition mechanism to achieve self-selection and self-locking of circularly polarized lasing. Circularly polarized modes with lower threshold gain are preferentially lased, and mode competition suppresses other circularly polarized modes, eliminating the need for external polarizers or chiral mirrors, thus realizing a monolithically integrated circularly polarized semiconductor laser. In the vertically misaligned bichiral resonant cavity structure of this invention, high Q-value and strong chiral response can be achieved simultaneously. The two chiral layers work synergistically through vertical coupling, maintaining the high Q-value of the quasi-BIC mode while obtaining strong circular dichroism (CD), resolving the inherent contradiction of difficulty in simultaneously achieving high Q-value and strong chirality in single-layer structures. Attached Figure Description

[0027] Figure 1 is a schematic diagram of the overall structure of the vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser provided in an embodiment of the present invention.

[0028] Figure 2 is a schematic diagram of the planar structure of the first chiral photonic crystal cavity and the second chiral photonic crystal cavity provided in the embodiment of the present invention; wherein, (a) shows the periodic arrangement of “S” type chiral units, and (b) shows the periodic arrangement of “C” type chiral units.

[0029] Figure 3 is a schematic diagram of the planar structure of the first chiral unit provided in an embodiment of the present invention; wherein, (a) shows a schematic diagram of relative translation and (b) shows a schematic diagram of relative rotation.

[0030] Figure 4 is a schematic diagram of the cross-sectional structure of the first chiral unit and the second chiral unit provided in the embodiment of the present invention; wherein, (a) shows a schematic diagram of the etching depth of the first chiral unit, and (b) shows a schematic diagram of the etching depth of the second chiral unit.

[0031] Figure 5 is a schematic flowchart of the fabrication method of the vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser provided by the present invention.

[0032] Figure 6 is a schematic diagram comparing the radiation loss of the left-hand circular polarization mode and the right-hand circular polarization mode provided in the embodiment of the present invention.

[0033] In the picture: 1. n-type GaAs substrate; 2. n-type Al0.3GaAs cladding; 3. n-type Al0.2GaAs / GaAs mirror; 4. GaInP first chiral photonic crystal cavity; 5. n-type GaAs first regeneration buffer layer; 6. In0.15GaAs / GaAs quantum well light-emitting active region; 7. GaInP second chiral photonic crystal cavity; 8. GaAs second regeneration buffer layer; 9. p-type Al0.2GaAs cladding; 10. p+ type GaAs current spreading layer; 11. p++ type GaAs current injection layer; 401. First chiral cell; 402. First chiral cell etched hole; 701. Second chiral cell; 702. Second chiral cell etched hole. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings: To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings, taking an InGaAs / GaAs semiconductor laser with a lasing wavelength of 980 nm as an example.

[0037] like Figure 1 As shown, the vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser of the present invention includes an n-type GaAs semiconductor substrate 1 and an n-type Al semiconductor substrate 1 arranged sequentially from bottom to top. 0.3 GaAs cladding 2, n-type Al 0.2 3. GaAs / GaAs mirror; 4. GaInP first chiral photonic crystal cavity; 5. n-type GaAs first regeneration buffer layer; 6. In 0.15 6. GaAs / GaAs quantum well light-emitting active region; 7. GaInP second chiral photonic crystal cavity; 8. GaAs second regeneration buffer layer; 9. p-type Al 0.2 GaAs cladding layer 9, p+ type GaAs current spreading layer 10, and p++ type GaAs current injection layer 11.

[0038] Specifically: The n-type GaAs semiconductor substrate 1 of this invention has a crystal orientation of (100), an initial thickness of 650 μm, and a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0039] The n-type Al of the present invention 0.3 The GaAs cladding layer 2 has a thickness of 800 nm and a doping concentration of 1.5 × 10⁻⁶. 18 cm -3 .

[0040] The n-type Al of the present invention 0.2 The GaAs / GaAs mirror 3 has 38 pairs and a reflectivity of 98%.

[0041] The GaInP first-chirality photonic crystal cavity 4 of the present invention has a thickness of 400 nm and is treated without doping.

[0042] The thickness of the first regeneration buffer layer 5 of the n-type GaAs in this invention is 20 nm, and the doping concentration is 1.5 × 10⁻⁶. 18 cm -3 .

[0043] The In of the present invention 0.15 The GaAs / GaAs quantum well light-emitting active region 6 is an asymmetric compressive strain structure, in which In 0.15The GaAs potential well has a thickness of 5 nm, a band gap wavelength of 980 nm, is subjected to 1.8% compressive strain, and is undoped; the GaAs barrier layer has a thickness of 12 nm, is unstrained, and is undoped.

[0044] The GaInP second-chiral photonic crystal cavity 7 of the present invention has a thickness of 248 nm and is treated without doping.

[0045] The thickness of the second GaAs regeneration buffer layer 8 of the present invention is 20 nm, and it is treated without doping.

[0046] The p-type Al of the present invention 0.2 The GaAs cladding layer 9 has a thickness of 550 nm and a doping concentration of 2 × 10⁹. 18 cm -3 .

[0047] The p+ type GaAs current spreading layer 10 of this invention has a thickness of 50 nm and a doping concentration of 3.5 × 10⁻⁶. 18 cm -3 .

[0048] The p++ type GaAs current injection layer 11 of this invention has a thickness of 20 nm and a doping concentration of 5.5 × 10⁻⁶. 18 cm -3 .

[0049] The vertical spacing between the GaInP first chiral photonic crystal cavity 4 and the GaInP second chiral photonic crystal cavity 7 of the present invention is set to 380 nm to ensure that the internal optical field can be strongly coupled into the chiral unit; the GaInP first chiral photonic crystal cavity 4 is located in In 0.15 The near-field high-field region vertically downwards from the GaAs / GaAs luminescent active region 6, and the GaInP second-chiral photonic crystal cavity 7 located in In 0.15 The near-field high-field region vertically above the GaAs / GaAs luminescent active region 6 together constitutes a vertically displaced bipolar photonic crystal resonant cavity, forming resonant coupling and supporting quasi-continuous domain bound state modes (q-BIC).

[0050] like Figure 2 As shown, the lattice constant of the GaInP first-chirality photonic crystal cavity 4 is... a 1 = 385 nm, the lattice constant of the GaInP second-chirality photonic crystal cavity 7. a 2 = 389 nm, and the target lasing wavelength of 980 nm both fall within the photonic band gaps of the GaInP first chiral photonic crystal cavity 4 and the GaInP second chiral photonic crystal cavity 7. The first chiral unit 401 is "S" shaped, and the second chiral unit 701 is "C" shaped, both employing an air-hole structure.

[0051] like Figure 3 As shown, the relative rotation angle between the first chiral unit 401 and the second chiral unit 701 is 12°, and the relative translation amounts in the x and y directions are 0.015° and 0.015° respectively. a 1 and 0.012 a 1.

[0052] like Figure 4 As shown, the depth of the first chiral unit etched hole 402 of the first chiral unit 401 is 245 nm, and the depth of the second chiral unit etched hole 702 of the second chiral unit 701 is 248 nm. The etching ratio of the etched hole 402 of the first chiral unit 401 is 0.6125, and the etching ratio of the etched hole 702 of the second chiral unit 701 is 1.

[0053] like Figure 5 As shown, the fabrication method of the vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser of this embodiment includes: S1: Provides a semiconductor substrate, and sequentially epitaxially grows an n-type cladding layer and an n-type DBR mirror; Specifically, it includes: 1) An n-type GaAs substrate 1 was selected, with a crystal orientation of (100), an off-center angle of 2°~4°, an initial thickness of 650 μm, and a doping concentration of 2×10⁻⁶. 18 cm -3 The n-type GaAs substrate 1 is first subjected to standard organic cleaning: acetone cleaning - isopropanol cleaning - deionized water rinsing - nitrogen drying; then it is sent into the MOCVD chamber for high-temperature baking pretreatment at 625℃ for 3 minutes to remove the surface oxide layer.

[0054] 2) Epitaxial growth of n-type Al on n-type GaAs substrate 1 0.3 GaAs cladding 2: Growth temperature 605℃, V / III ratio 45, growth thickness 800 nm, Si doping concentration 1.5×10⁻⁶ 18 cm -3 .

[0055] 3) In n-type Al 0.3 GaAs cladding layer 2 epitaxial n-type Al 0.2 GaAs / GaAs mirror 3: 38 periodic pairs, reflectivity 98%; optical thickness of each layer is 1 / 4 of the working wavelength; growth temperature 605~615℃, V / III ratio 40~50; growth rate 0.8~1.2nm / s.

[0056] S2: An epitaxial first chiral photonic crystal cavity is extended at the first vertical position; Specifically, it includes: In n-type Al 0.2The GaInP first-chiral photonic crystal cavity 4 is fabricated on the GaAs / GaAs mirror 3 with a thickness of 400 nm, a growth temperature of 600 °C, a V / III ratio of 42, and no intrinsic doping. The first vertical position is set to a downward vertical distance of 120 nm from the light-emitting active region. After the epitaxy of this layer is completed, the wafer is removed and subjected to MOCVD, followed by photolithography-etching process to fabricate the first-chiral photonic crystal pattern.

[0057] S3: Fabricate a first chiral unit on the first chiral photonic crystal cavity, and then epitaxially grow a first regeneration buffer layer; Specifically, it includes: 1) The photoresist AR-P6200 used for electron beam exposure was spin-coated on the GaInP first-chiral photonic crystal cavity 4, with a thickness of 240-280 nm; the pattern of the first chiral unit 401 was prepared by electron beam exposure; the pattern structure is "S" type, and the lattice constant is 385 nm; the pattern of the first chiral unit 401 was etched by ICP inductively coupled plasma dry etching, with an etching depth of 245 nm and an etching ratio of 0.6125, which did not completely penetrate the cavity core layer; after etching, the photoresist was removed by wet stripping.

[0058] 2) The wafer is fed into an MOCVD layer for re-epitaxy of n-type GaAs first regeneration buffer layer 5. The material is GaAs, the thickness is 20 nm, and the doping concentration is 1.5 × 10⁻⁶. 18 cm -3 The growth temperature is 580~595℃, the V / III ratio is 50~60, the growth rate is 0.6~0.9nm / s, and the photonic crystal pores are not filled.

[0059] S4: Continue to extend the light-emitting active region; Specifically, it includes: Epitaxial growth of In on GaAs first regeneration buffer layer 5 0.15 GaAs / GaAs quantum well light-emitting active region 6, In 0.15 A GaAs / GaAs quantum well achieving 980 nm in size was grown at a temperature of 560–580 °C with a V / III ratio of 62–78; neither the quantum well nor the barrier was doped. In was also present. 0.15 The GaAs potential well has a thickness of 5 nm and is subjected to a compressive strain of 1.8%, while the GaAs barrier layer has a thickness of 12 nm and is unstrained.

[0060] S5: A second chiral photonic crystal cavity is extended at the second vertical position; Specifically, it includes: In 0.15A GaInP second-chiral photonic crystal cavity 7 is fabricated on the GaAs / GaAs quantum well light-emitting active region 6: the thickness is 248 nm, the growth temperature is 600℃, the V / III ratio is 42, and it is intrinsically undoped; the second vertical position is set to be 80 nm above the light-emitting active region; after the epitaxy of this layer is completed, the wafer is removed and MOCVD is performed, and the second chiral unit 701 is fabricated by photolithography-etching process.

[0061] S6: Fabricate a second chiral unit with a preset rotation angle or translation displacement relative to the first chiral unit on the second chiral photonic crystal cavity; Specifically, it includes: 1) The photoresist AR-P6200 used for electron beam exposure was spin-coated onto the GaInP second-chiral photonic crystal cavity 7, with a thickness of 240-280 nm; the first chiral unit 701 pattern was prepared by electron beam exposure; the pattern structure is "C" type, and the lattice constant is 388 nm; the first chiral unit 701 pattern was etched by ICP inductively coupled plasma dry etching, with an etching depth of 248 nm and an etching ratio of 1, completely penetrating the cavity core layer; after etching, the photoresist was removed by wet stripping.

[0062] 2) The relative rotation angle between the first chiral unit 401 and the second chiral unit 701 obtained by etching is 12°, and the relative translation amounts in the x and y directions are 0.015° and 0.015° respectively. a 1 and 0.012 a 1.

[0063] S7: Then, sequentially epitaxially grow a second regrowth buffer layer, a p-type cladding layer, a current spreading layer, and a current injection layer; Specifically, it includes: 1) The wafer is fed into MOCVD, and a second GaAs regeneration buffer layer 8 is epitaxially grown on the GaInP second chiral photonic crystal cavity 7. The material is GaAs, the thickness is 20 nm, and the doping concentration is 1.5 × 10⁻⁶. 18 cm -3 The growth temperature is 580~595℃, the V / III ratio is 50~60, the growth rate is 0.6~0.9nm / s, and the photonic crystal pores are not filled.

[0064] 2) Epitaxial growth of p-type Al on GaAs second regeneration buffer layer 8 0.2 GaAs cladding 9: 550 nm thick, doping concentration 2 × 10⁹ 18 cm -3 The growth temperature is 612℃ and the V / III ratio is 48.

[0065] 3) In p-type Al 0.2An epitaxial p+ type GaAs current-spreading layer 10, with a thickness of 50 nm and a doping concentration of 3.5 × 10⁻⁶, is formed on the GaAs cladding layer 9. 18 cm -3 Growth temperature 624℃, V / III ratio 50.

[0066] 4) A p++ type GaAs current injection layer 11 with a thickness of 20 nm and a doping concentration of 5.5 × 10⁻⁶ is epitaxially grown on the p+ type GaAs current extension layer 10. 18 cm -3 This ensures the formation of a good p-type ohmic contact electrode.

[0067] S8: Fabrication of metal electrode structure; Specifically, it includes: 1) p-side electrode: A window is made on the surface of the p++ type GaAs current injection layer 11 by photolithography, and ohmic contact metals of Ti (20nm) / Pt (455nm) / Au (550nm) are deposited by electron beam evaporation, and then the p-electrode pattern is formed by wet lift-off. 2) The n-type GaAs substrate 1 was thinned to 120 μm by grinding; 3) n-side electrode: AuGe (34nm) / Ni (15nm) / Au (350nm) are vapor-deposited on the back side of the n-type GaAs substrate 1 to form the n-side ohmic contact electrode.

[0068] S9: Complete laser chip fabrication, annealing, passivation, cleavage, and packaging; Specifically, it includes: 1) Rapid thermal annealing: Annealing is performed at 390℃ in a nitrogen atmosphere for 45 seconds to obtain p / n electrode ohmic contact.

[0069] 2) Passivation: A SiO2 passivation layer with a thickness of 120 nm was deposited using PECVD.

[0070] 3) Etching the isolation channel: Using ICP process, adjacent lasers are etched and separated, with the isolation channel depth reaching n-type Al. 0.3 GaAs cladding layer 2 enables electrical isolation between chips.

[0071] 4) Cleavage: Cleavage along the {110} crystal direction of the n-type GaAs substrate 1 to obtain an independent vertically displaced bipolar cavity two-dimensional photonic crystal semiconductor laser chip; 5) Packaging: The chip is soldered onto an aluminum nitride or diamond carrier and then packaged by gold wire bonding to obtain a vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser.

[0072] like Figure 6 As shown, the radiation loss of the left-hand circularly polarized mode α LApproximately 96 cm -1 Radiation loss of right-hand circularly polarized mode α R 25 cm -1 The loss ratio is close to 4:1; the corresponding Q values ​​are Q L =2800 and Q R =8000, Q value difference reaches 65%, which is far better than the 5%~15% of single-layer chiral structure; the circular polarization degree of the output laser can reach more than 0.92.

[0073] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A vertically misaligned bipolar cavity two-dimensional photonic crystal semiconductor laser, characterized in that, The device comprises, from bottom to top, a semiconductor substrate, an n-type cladding, an n-type mirror, a first chiral photonic crystal cavity, a first regeneration buffer layer, a light-emitting active region, a second chiral photonic crystal cavity, a second regeneration buffer layer, a p-type cladding, a current spreading layer, and a current injection layer, wherein a p-plane electrode is formed on the upper surface of the current injection layer, and an n-plane electrode is formed on the lower surface of the semiconductor substrate. The first chiral photonic crystal cavity and the second chiral photonic crystal cavity together form a vertically misaligned bichiral photonic crystal resonant cavity. The first chiral unit in the first chiral photonic crystal cavity and the second chiral unit in the second chiral photonic crystal cavity have relative displacement in the plane, and there is a non-zero vertical spacing between the two layers to form a bichiral non-mirror symmetrical resonant structure. This allows the first chiral photonic crystal cavity and the second chiral photonic crystal cavity to be coupled to the same laser resonant mode, and the left-hand circular polarization mode and the right-hand circular polarization mode to have different radiation losses or different threshold gains. The relative displacement includes at least one of relative rotation and relative translation.

2. The photonic crystal semiconductor laser according to claim 1, characterized in that, The first chiral unit and the second chiral unit include one or more combinations of chiral structures such as L-shaped holes, S-shaped holes, C-shaped holes, windmill-shaped holes, and eccentric elliptical holes; and the filling material in the holes includes one or more combinations of air, chiral materials, and III-V compound semiconductor materials.

3. The photonic crystal semiconductor laser according to claim 1, characterized in that, The relative rotation angle between the first chiral unit and the second chiral unit is 0°~90°, and the relative translation amount between the first chiral unit and the second chiral unit is 0.01a1~0.50a1 or 0.01a2~0.50a2 in the x and y directions, respectively; where a1 is the lattice constant of the first chiral photonic crystal cavity and a2 is the lattice constant of the second chiral photonic crystal cavity.

4. The photonic crystal semiconductor laser according to claim 1, characterized in that, The first chiral unit and the second chiral unit have different etching depths, forming an asymmetric effective refractive index modulation and asymmetric radiation coupling channel; the first chiral photonic crystal cavity and the second chiral photonic crystal cavity have the same lattice constant or different lattice constants, forming a resonant coupling cavity structure.

5. The photonic crystal semiconductor laser according to claim 1, characterized in that, The vertical spacing between the first chiral photonic crystal cavity and the second chiral photonic crystal cavity is 10 nm-1000 nm; the material system of the first chiral photonic crystal cavity and the second chiral photonic crystal cavity includes one of the semiconductor material systems of GaAs, InP, InGaAsP, GaInP, GaN, InGaN, AlGaN, and GaSb.

6. The photonic crystal semiconductor laser according to claim 1, characterized in that, The first chiral photonic crystal cavity is located in the near-field high-field region vertically below the light-emitting active region, and the second chiral photonic crystal cavity is located in the near-field high-field region vertically above the light-emitting active region; or, the first chiral photonic crystal cavity and the second chiral photonic crystal cavity are both located on the same side of the light-emitting active region but at different etching depths.

7. The photonic crystal semiconductor laser according to claim 1, characterized in that, The vertically misaligned bipolar photonic crystal resonator is used to support one or more of the following: band-edge mode, quasi-continuous bound state mode, and guided mode resonance mode. The radiation loss of the left-hand circularly polarized mode and the right-hand circularly polarized mode are different. The vertically misaligned bipolar photonic crystal resonator makes the quality factor difference between the left-hand circularly polarized mode and the right-hand circularly polarized mode greater than 5%, and the vertically misaligned bipolar photonic crystal resonator makes the circular polarization degree of the output chiral laser better than 0.

6.

8. The photonic crystal semiconductor laser according to claim 1, characterized in that, The light-emitting active region includes any one of a single quantum well, multiple quantum wells, quantum dot, and quantum cascade active region; the metal electrode structure includes a p-type metal electrode and an n-type metal electrode, wherein the p-type metal electrode is a ring electrode, a mesh electrode, or a transparent conductive electrode. The n-type metal electrode is a mode-matching electrode.

9. The photonic crystal semiconductor laser according to claim 1, characterized in that, The semiconductor material system of the photonic crystal semiconductor laser is InGaN / GaN, GaAs / AlGaAs, InGaAs / GaAs, InP / InGaAsP, InP / InAlGaAs, GaSb / AlGaSb, InAs / GaSb, or a terahertz quantum cascade semiconductor material system; the first regeneration buffer layer and the second regeneration buffer layer can respectively fill the first chiral unit and the second chiral unit, with a filling ratio greater than 0, reducing the roughness of the sidewalls of the first chiral unit and the second chiral unit, and improving the interlayer coupling consistency; the thickness of the first regeneration buffer layer and the second regeneration buffer layer is set to 10 nm-100 nm.

10. A method for fabricating a photonic crystal semiconductor laser according to any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Provide a semiconductor substrate and sequentially epitaxially grow an n-type cladding layer and an n-type mirror; Step 2: Extend the first chiral photonic crystal cavity at the first vertical position; Step 3: Fabricate a first chiral unit on the first chiral photonic crystal cavity, and then epitaxially grow a first regeneration buffer layer; Step 4: Continue epitaxial growth of the active light-emitting region; Step 5: Extend a second chiral photonic crystal cavity at the second vertical position; Step 6: Fabricate a second chiral unit with a preset rotation angle or translational displacement relative to the first chiral unit on the second chiral photonic crystal cavity; Step 7: Then, sequentially epitaxially grow a second regrowth buffer layer, a p-type cladding layer, a current spreading layer, and a current injection layer; Step 8: Prepare the metal electrode structure; Step 9: Complete the laser chip fabrication, annealing, passivation, cleaving, and packaging.

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