A tristate light-emitting quantum dot superluminescent light-emitting diode and a manufacturing method thereof

Abstract

The present invention relates to a three - state light - emitting quantum dot superluminescent light - emitting diode and a manufacturing method thereof. The key point of the technical solution is that the superluminescent light - emitting diode includes a bar, and the bar includes an N - GaAs substrate layer, an N - GaAs buffer layer, an N - AlGaAs lower cladding layer, a GaAs lower waveguide layer, an In(Ga)As quantum dot active region, a GaAs upper waveguide layer, a P - AlGaAs upper cladding layer, and a P + - GaAs ohmic contact layer arranged in sequence from bottom to top; a ridge waveguide that intersects the central plane of the bar obliquely is arranged on the top surface of the bar; an antireflection coating of ZrO2 with a central wavelength of 1000 nm is arranged on the front cavity surface of the bar; a plurality of pairs of high - reflection coatings of Ta2O5 / SiO2 with a central wavelength of 880 nm are arranged on the rear cavity surface of the bar; the manufacturing method includes step S1, epitaxial structure growth; step S2, ridge waveguide etching process; step S3, electrode processing; step S4, optical coating processing; the superluminescent light - emitting diode of the present invention can simultaneously have the characteristics of high power and wide spectrum, and can be well applied to incoherent optical systems such as OCT systems.

Description

Technical Field

[0001] The present invention relates to the technical field of superluminescent diodes, and particularly to a three-state light-emitting quantum dot superluminescent diode and a manufacturing method thereof. Background Art

[0002] A superluminescent diode (SLD) is a kind of incoherent light source that utilizes amplified spontaneous emission. It combines the high power of a laser and the broad spectral characteristics of a light-emitting diode, and at the same time has weak temporal coherence and high fiber coupling efficiency, making it an ideal light source for some incoherent optical systems (such as an optical coherence tomography system OCT). Currently, the main light source of OCT systems is a near-infrared quantum well superluminescent diode. However, such light sources often have the problem that high power and broad spectrum restrict each other, and cannot well meet the requirements of OCT systems, resulting in poor imaging resolution and the inability to fully display fine structures. In addition, due to the strong scattering of biological tissues at shorter wavelengths, the current detection depth of this technology is relatively small, only 1-2 mm. Therefore, developing a near-infrared superluminescent diode with both high power and broad spectral characteristics is a key factor in improving the resolution and detection depth of OCT technology.

[0003] In order to improve the performance of quantum well superluminescent diodes (QW-SLDs), various methods have been adopted, such as using a chirped quantum well structure or combining the high-order transition emission of a quantum well structure. However, the carrier distribution and photon reabsorption in an asymmetric multi-quantum well structure are still problems of the above devices. Due to the intrinsic inhomogeneous broadening, quantum dot materials are expected to break the restriction between output power and full width at half maximum. Since the ground state saturation gain of quantum dots is relatively low, the ground state emission of quantum dots can reach its saturation power at a lower injection current. Compared with quantum well superluminescent diodes, the excited state emission of quantum dots is more likely to occur. Although significant progress has been made in quantum dot superluminescent diodes (QD-SLEDs), the spectral emission of quantum dot superluminescent diodes is limited to the ground state of quantum dots or the ground state and the first excited state. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a three-state light-emitting quantum dot superluminescent diode, which can simultaneously have the characteristics of high power and broad spectrum and can be well applied to incoherent optical systems such as OCT systems.

[0005] The above technical purpose of the present invention is achieved through the following technical solutions: A three-state light-emitting quantum dot superluminescent diode includes a bar, and the bar includes an N-GaAs substrate layer, an N-GaAs buffer layer, an N-AlGaAs lower cladding layer, a GaAs lower waveguide layer, an In(Ga)As quantum dot active region, a GaAs upper waveguide layer, a P-AlGaAs upper cladding layer, and a P arranged in sequence from bottom to top. +-GaAs ohmic contact layer;

[0006] The top surface of the bar has a ridge waveguide that intersects obliquely with the central plane of the bar;

[0007] The front cavity surface of the bar is provided with an antireflection coating of ZrO with a central wavelength of 1000 nm; 2 The rear cavity surface of the bar is provided with several pairs of high reflection coatings of Ta with a central wavelength of 880 nm; 2 O 5 / SiO 2 High reflection coating.

[0008] Preferably, the width of the ridge waveguide is 8 μm.

[0009] Preferably, the angle between the ridge waveguide and the central plane of the bar is 7°.

[0010] Another object of the present invention is to provide a method for manufacturing a three-state light-emitting quantum dot superluminescent diode for manufacturing the above three-state light-emitting quantum dot superluminescent diode.

[0011] The above technical object of the present invention is achieved by the following technical solutions: A method for manufacturing a three-state light-emitting quantum dot superluminescent diode includes the following steps:

[0012] Step S1, epitaxial structure growth: Growing an N-GaAs buffer layer, an N-AlGaAs lower cladding layer, a GaAs lower waveguide layer, an In(Ga)As quantum dot active region, a GaAs upper waveguide layer, a P-AlGaAs upper cladding layer, and a P + -GaAs ohmic contact layer on an N-GaAs substrate layer to form an epitaxial wafer;

[0013] Step S2, ridge waveguide etching process: Depositing a silicon oxide dielectric layer on the surface of the epitaxial wafer, lithographically forming a ridge waveguide pattern, and etching the ridge waveguide by dry etching until reaching 200 nm from the active region; Growing a silicon oxide insulating layer on the surface of the epitaxial wafer again;

[0014] Step S3, electrode processing; Drilling holes on the surface of the ridge waveguide, evaporating P-side metal, thinning and polishing, evaporating N-side metal, and alloying to form an ohmic contact;

[0015] Step S4, optical coating processing: Dissociating the epitaxial wafer to obtain a bar, evaporating an antireflection coating of ZrO on the front cavity surface of the bar; 2 Evaporating Ta on the rear cavity surface of the bar; 2 O 5 / SiO 2 High reflection coating. Description of the drawings

[0016] The accompanying drawings, which form a part of the specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the present invention.

[0017] Figure 1 It is a schematic diagram of the bar layer structure.

[0018] Figure 2 It is a schematic diagram of the structure of a three-state light-emitting quantum dot superluminescent diode.

[0019] Figure 3 It is a top view of a three-state light-emitting quantum dot superluminescent diode.

[0020] Figure 4 It is ZrO 2 antireflection coating and Ta 2 O 5 / SiO 2 Simulated diagram of the reflectivity of the high-reflection coating.

[0021] Figure 5 It is a graph of the optical characteristics of a three-state light-emitting quantum dot superluminescent diode.

[0022] Wherein: 1, N-GaAs substrate layer; 2, N-GaAs buffer layer; 3, N-AlGaAs lower cladding layer; 4, GaAs lower waveguide layer; 5, In(Ga)As quantum dot active region; 6, GaAs upper waveguide layer; 7, P-AlGaAs upper cladding layer; 8, P + -GaAs ohmic contact layer; 9, ridge waveguide; 100, ZrO 2 antireflection coating; 200, Ta 2 O 5 / SiO 2 high-reflection coating. Detailed implementation manners

[0023] The present invention will be further described in detail below with reference to the accompanying drawings. The same reference numerals are used for the same components. It should be noted that the terms "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to the directions in the drawings, and the terms "bottom surface" and "top surface", "inner" and "outer" refer to the directions towards or away from the geometric center of a specific component, respectively.

[0024] Example 1:

[0025] A three-state light-emitting quantum dot superluminescent diode, hereinafter referred to as a quantum dot superluminescent diode, with reference to Figures 1 to 3, including a stripe, the stripe includes an N-GaAs substrate layer 1, an N-GaAs buffer layer 2, an N-AlGaAs lower cladding layer 3, a GaAs lower waveguide layer 4, an In(Ga)As quantum dot active region 5, a GaAs upper waveguide layer 6, a P-AlGaAs upper cladding layer 7, and a P + -GaAs ohmic contact layer 8 from bottom to top. Among them, the In(Ga)As quantum dot active region 5 uses 5 layers (not limited to 5 layers) of InAs quantum dot material layers; each layer of InAs quantum dot material layer includes 2ML InAs and 5MLIn 0.18 Ga 0.82 As strain buffer layer. The top surface of the stripe is provided with a ridge waveguide 9 that intersects obliquely with the central plane of the stripe; the width W of the ridge waveguide 9 is 8 μm. The angle θ between the ridge waveguide 9 and the central plane of the stripe is 7°. The front cavity surface of the stripe is provided with an antireflection coating 100 with a central wavelength of 1000 nm; the rear cavity surface of the stripe is provided with several pairs of high reflection coatings 200 with a central wavelength of 880 nm 2 Ta 2 O 5 / SiO 2 .

[0026] Figure 4 is the reflectivity simulation diagram of the antireflection coating of ZrO 2 and the Ta 2 O 5 / SiO 2 high reflection coating. By simulating the reflectivity of the antireflection coating 100 of ZrO 2 and the Ta2O 5 / SiO 2 high reflection coating 200, Figure 4 (a) in is the reflectivity curve of the antireflection coating 100 of ZrO 2 , Figure 4 (b) in is the reflectivity curve of the Ta2O 5 / SiO 2 high reflection coating. It can be seen from Figure 4 that the reflectivities of the second excited state and the first excited state of the Ta 2 O 5 / SiO 2 high reflection coating are about 90% and 43% respectively, while the ground state reflectivity is only 4%; the reflectivity of the antireflection coating 100 of ZrO 2 for all quantum dot emission energy levels is about 5%.

[0027] The quantum dot superluminescent diode is placed on a copper heat sink, and its output characteristics are tested under continuous current injection at room temperature. Figure 5 is the optical characteristic curve of the measured quantum dot superluminescent diode. Among themFigure 5 In (a) is the emission spectrum diagram of the quantum dot superradiant light-emitting diode, and (b) is the power-current curve diagram of the input power supply. From Figure 4 it can be seen that at a driving current of 100 mA, the emission spectral peak position can be seen at 1066 nm in the electroluminescence spectrum, and this emission peak corresponds to the ground state emission of the quantum dots. As the driving current increases from 1000 mA to 1500 mA, a second emission peak at 1032 nm can be seen in the electroluminescence spectrum, and this emission peak corresponds to the first excited state emission of the quantum dots. Further increasing the driving current, while maintaining the ground state and first excited state emissions of the quantum dots, a third emission peak can be seen at 988 nm in the electroluminescence spectrum, corresponding to the excited state of the quantum dots. This is the first superradiant light-emitting diode that realizes simultaneous emission of three states based on quantum dot materials. Because the degeneracy of the excited state of the quantum dots is relatively large, so from Figure 5 the P-I curve of (b), it can be seen that with the emission of the second excited state, the slope efficiency increases, and the output power can reach up to 40 mW at most. The superradiant light-emitting diode with simultaneous emission of three states has a relatively large continuous output power (40 mW) on the premise of a relatively wide emission spectrum (full width at half maximum of 91 nm).

[0028] The principle of the specific embodiment of this embodiment is as follows:

[0029] For quantum dot materials, the internal carriers have a three-dimensional quantum confinement effect, so they are called artificial atoms and thus have the unique property of discrete energy levels. Therefore, the ground state (ground state), first excited state (first excited state), and second excited state (second excited state) of quantum dot materials have different energy level degeneracies, which are 2, 4, and 8 respectively. For traditional superradiant light-emitting diode devices, generally it is the ground state or the emission of the ground state + first excited state, and the second excited state does not participate in the emission. The main reason is that the electrically injected carriers will first relax to the ground state of the quantum dots to recombine and emit light, and the carriers in the first excited state and the second excited state accumulate slowly. However, if the number of carriers in the ground state or the first excited state increases to meet the lasing threshold, most of the injected carriers will recombine through stimulated emission and will not continue to accumulate at the second excited state energy level.

[0030] For a quantum dot structure, the electrically injected carriers are first trapped by the wetting layer and then relaxed to the high-energy excited state of the quantum dots. Due to the three-dimensional carrier confinement effect, the energy levels inside the dots are discrete levels similar to atoms, and the higher energy levels have a higher degeneracy. The carriers first relax to the ground state with the lowest energy level for radiative recombination. As the injection increases, the carriers will also slowly accumulate in the excited state. Moreover, when the relaxation rate of the carriers inside the dots is slow, the accumulation of carriers in the excited state will gradually increase. However, in order to ensure the continuous accumulation of carriers in the excited state energy level, the prerequisite is that there is no lasing in the ground state energy level because the lasing recombination rate is very high and it is difficult for the carriers to stay in the excited state continuously. The primary prerequisite for achieving multi-level luminescence is to ensure that the ground state of the quantum dots is always in a non-lasing state. Moreover, in order to achieve simultaneous multi-state luminescence, it is also crucial to reduce the number of carriers required for the excited state to enter the super-radiant state. Therefore, by setting an anti-reflection coating 100 with a central wavelength of 1000 nm on the front cavity surface of the bar, and several pairs of high-reflection coatings 200 with a central wavelength of 880 nm on the rear cavity surface of the bar, the low reflectivity in the state band has a higher reflectivity in the first excited state band and an even higher reflectivity in the second excited state band, thereby realizing a super-radiant light-emitting diode with the characteristics of both high power and wide spectrum. 2 An anti-reflection coating 100; several pairs of Ta 2 O 5 / SiO 2 high-reflection coatings 200 are provided on the rear cavity surface of the bar, so that the low reflectivity in the state band has a higher reflectivity in the first excited state band and an even higher reflectivity in the second excited state band, and thus a super-radiant light-emitting diode is realized, which can simultaneously have the characteristics of high power and wide spectrum.

[0031] Example 2:

[0032] A manufacturing method of a three-state luminescent quantum dot super-radiant light-emitting diode, comprising the following steps:

[0033] Step S1, epitaxial structure growth: On the N-GaAs substrate layer, an N-GaAs buffer layer, an N-AlGaAs lower cladding layer, a GaAs lower waveguide layer, an In(Ga)As quantum dot active region, a GaAs upper waveguide layer, a P-AlGaAs upper cladding layer, and a P + -GaAs ohmic contact layer are sequentially epitaxially grown by a solid-source molecular beam epitaxy (MBE) reactor in the crystal growth direction to form an epitaxial wafer.

[0034] Step S2, ridge waveguide etching process: Deposit a silicon oxide dielectric layer on the surface of the epitaxial wafer, prepare a mask pattern of the ridge waveguide through ultraviolet lithography technology, and then use a dry etching combined with wet etching method to etch to a position 200 nm away from the active region to prepare an 8-μm-wide ridge waveguide structure; grow a silicon oxide insulating layer on the surface of the epitaxial wafer again;

[0035] Step S3, electrode processing: Fabricate an electrical contact window on the top of the ridge through ultraviolet lithography and reactive ion etching (RIE); Evaporate the p-side electrical contact electrode (e.g., Ti / Au) of the device by electron beam evaporation technology, then thin and polish the substrate to about 110 μm to minimize self-heating effects, and evaporate the n-side electrical contact electrode (e.g., Ni / AuGe / Ni / Au) on the back of the device by electron beam evaporation. Subsequently, alloy for 60 seconds at 400 °C in a nitrogen atmosphere to form an ohmic contact. Evaporate the Ti / Au top contact electrode by electron beam evaporation, then thin the substrate to about 110 μm to minimize self-heating effects, and deposit Ni / AuGe / Ni / Au on the back of the wafer. Then alloy for 60 seconds at 400 °C in a nitrogen atmosphere.

[0036] Step S4, optical coating processing: Dissociate the epitaxial wafer to obtain a bar, and evaporate ZrO 2 antireflection coating on the front cavity surface of the bar; Evaporate Ta 2 O 5 / SiO 2 high reflection coating on the back cavity surface of the bar.

[0037] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and not for limiting the scope of the present invention. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A three - state light - emitting quantum dot superluminescent light - emitting diode, comprising a bar - like structure, characterized in that: The bar - like structure includes an N - GaAs substrate layer (1), an N - GaAs buffer layer (2), an N - AlGaAs lower cladding layer (3), a GaAs lower waveguide layer (4), an In(Ga)As quantum dot active region (5), a GaAs upper waveguide layer (6), a P - AlGaAs upper cladding layer (7), and a P+-GaAs ohmic contact layer (8) arranged successively from bottom to top; A ridge waveguide (9) that intersects the central plane of the bar - like structure obliquely is provided on the top surface of the bar - like structure; The front cavity surface of the bar is provided with ZrO with a central wavelength of 1000nm. 2 The anti-reflection film coating (100); the rear cavity surface of the bar is provided with a plurality of pairs of Ta with a central wavelength of 880nm 2 O 5 / SiO 2 The high reflective coating (200) has a higher reflectivity in the first excited state band and an even higher reflectivity in the second excited state band.

2. The three - state light - emitting quantum dot superluminescent light - emitting diode according to claim 1, characterized in that: The width of the ridge waveguide (9) is 8 μm.

3. The three - state light - emitting quantum dot superluminescent light - emitting diode according to claim 1, characterized in that: The included angle between the ridge waveguide (9) and the central plane of the bar - like structure is 7°.

4. A manufacturing method of a three - state light - emitting quantum dot superluminescent light - emitting diode, characterized in that, comprises the following steps: Step S1, epitaxial structure growth: Growing an N - GaAs buffer layer, an N - AlGaAs lower cladding layer, a GaAs lower waveguide layer, an In(Ga)As quantum dot active region, a GaAs upper waveguide layer, a P - AlGaAs upper cladding layer, and a P+-GaAs ohmic contact layer on the N - GaAs substrate layer to form an epitaxial wafer; Step S2, ridge waveguide etching process: Depositing a silicon oxide dielectric layer on the surface of the epitaxial wafer, lithographically forming a ridge waveguide pattern, and etching the ridge waveguide by dry etching until reaching 200 nm away from the active region; Growing a silicon oxide insulating layer on the surface of the epitaxial wafer again; Step S3, electrode processing; Drilling holes on the surface of the ridge waveguide, evaporating P - side metal, thinning and polishing, evaporating N - side metal, and alloying to form an ohmic contact; Step S4, optical coating process: Dissociate the epitaxial wafer to obtain a bar, and deposit ZrO 2 antireflection coating on the front cavity surface of the bar; deposit Ta 2 O 5 / SiO 2 high-reflection coating on the back cavity surface of the bar; the front cavity surface of the bar is provided with a ZrO 2 antireflection coating (100) with a central wavelength of 1000 nm; the back cavity surface of the bar is provided with several pairs of Ta 2 O 5 / SiO 2 high-reflection coatings (200); having a higher reflectivity in the first excited state band and an even higher reflectivity in the second excited state band.

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