High-power long-wave infrared quantum cascade laser and its manufacturing method

Abstract

The present invention discloses a high-power long-wave infrared quantum cascade laser and a method for manufacturing the same. The laser comprises: a laser unit, comprising a substrate, a lower waveguide layer, a lower optical confinement layer, an active layer, an upper optical confinement layer and an upper waveguide layer stacked in sequence; a groove structure formed by etching the laser unit, comprising a groove located at the front end cavity surface of the laser unit and a double groove located between the grooves, wherein both the double groove and the groove extend from the upper waveguide layer toward the substrate and pass through the active layer; a filling material filled in the groove structure, wherein the filling material comprises semi-insulating InP. The present invention etches a groove at the laser cavity surface, and then epitaxies a semi-insulating InP with high thermal conductivity, removes the cavity surface gain, greatly reduces the optical power density at the cavity surface, and improves the heat dissipation at the cavity surface, thereby optimizing the cavity surface thermal characteristics of the long-wave infrared quantum cascade laser, and improving the output power and device reliability.

Description

Technical Field

[0001] The invention relates to the technical field of infrared semiconductor optoelectronic devices, and in particular to a high-power long-wave infrared quantum cascade laser and a manufacturing method thereof. Background Art

[0002] Quantum cascade lasers are the most ideal semiconductor lasers in the medium and long-wave infrared bands. Compared with other types of medium and long-wave infrared lasers, they have the advantages of small size, high power density, direct electric pumping, etc., and have great application potential. On the one hand, the emission wavelength of quantum cascade lasers covers two important atmospheric windows of 3-5μm and 8-14μm. The atmospheric absorption and scattering losses of light in this band are smaller, and it is not easily affected by harsh environments such as turbid air, smoke, fog, haze, rain, and snow. At the same time, the background interference of solar radiation is low, so it has excellent atmospheric transmission characteristics. On the other hand, the characteristic absorption wavelengths of most gas molecules are located in this band, making this band an important band for precision spectral research. Therefore, quantum cascade lasers have become important laser devices for military infrared countermeasures, long-distance free-space optical communications, gas molecule detection, etc.

[0003] In application scenarios such as infrared countermeasures, free-space optical communications, and gas molecule telemetry, quantum cascade lasers are required to have both high power and high beam quality characteristics. High beam quality requires that the output cavity surface size of the quantum cascade laser be less than 10μm, which results in a very high power density at the output cavity surface of the quantum cascade laser. At the same time, when a high-power quantum cascade laser is working, the active layer will generate a lot of heat, and its active layer heat dissipation is extremely dependent on lateral heat dissipation. One side of the cavity surface is air or an oxide coating layer, which makes the heat dissipation channel at the cavity surface much less than other areas, and the temperature is also higher. The high optical power density and high temperature make the cavity surface of the high-power quantum cascade laser easy to burn, causing the laser to fail.

[0004] At present, the maximum output power of a single medium-wave infrared quantum cascade laser device has exceeded 5W, while the maximum power of a long-wave infrared quantum cascade laser is less than 4W. The reason for this is that the electro-optical conversion efficiency of the active layer of the medium-wave infrared quantum cascade laser is relatively high. More importantly, it is easier to achieve low-loss and high-quality cavity surface anti-reflection films in the medium-wave infrared band, which improves the cavity surface thermal characteristics of the quantum cascade laser to a certain extent. In contrast, the active layer of the long-wave infrared quantum cascade laser generates more heat, and there is a lack of effective means to improve the thermal characteristics at the cavity surface, which has become a bottleneck factor that currently limits the power increase of long-wave infrared quantum cascade lasers. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a high-power long-wave infrared quantum cascade laser and a method for manufacturing the same. By etching grooves on the laser cavity surface and then epitaxially growing semi-insulating InP with high thermal conductivity, the cavity surface gain is removed, the optical power density at the cavity surface is greatly reduced, and the heat dissipation at the cavity surface is improved, thereby optimizing the cavity surface thermal characteristics of the long-wave infrared quantum cascade laser and improving the output power and device reliability.

[0006] A first aspect of the present disclosure provides a high-power long-wave infrared quantum cascade laser, comprising:

[0007] A laser unit comprises a substrate, a lower waveguide layer, a lower optical confinement layer, an active layer, an upper optical confinement layer and an upper waveguide layer which are stacked in sequence;

[0008] A groove structure is formed by etching the laser unit, comprising a groove located at the front end cavity surface of the laser unit and a double groove located between the grooves, wherein the double groove and the groove both extend from the upper waveguide layer toward the substrate and pass through the active layer;

[0009] A filling material is filled in the trench structure, wherein the filling material includes semi-insulating InP.

[0010] Optionally, the filling material is Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm.

[0011] Optionally, the laser further comprises:

[0012] an insulating passivation layer, disposed on the upper waveguide layer;

[0013] A front electrode layer, provided on the insulating passivation layer;

[0014] The back electrode layer is arranged on a side of the substrate facing away from the lower waveguide layer.

[0015] Optionally, a ridge waveguide structure is formed between the double grooves, and an electric injection window is opened on the insulating passivation layer at a position corresponding to the ridge waveguide structure.

[0016] Optionally, the width of the double groove is 15 μm, the width of the ridge waveguide is 8 μm, and the width of the groove is 20 μm.

[0017] A second aspect of the present disclosure provides a method for manufacturing a high-power long-wave infrared quantum cascade laser, comprising:

[0018] Fabricating a laser unit, including sequentially growing a lower waveguide layer, a lower optical confinement layer, an active layer, an upper optical confinement layer, and an upper waveguide layer on a substrate;

[0019] Manufacturing a groove structure, including etching a laser unit to form a double groove and a groove, wherein the groove is located at the front end cavity surface of the laser unit, and the double groove is located between the grooves, and the double groove and the groove both extend from the upper waveguide layer toward the substrate and pass through the active layer;

[0020] A filling material including semi-insulating InP is filled in the trench structure.

[0021] Optionally, the filling material is Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm.

[0022] Optionally, the step of manufacturing the groove structure includes:

[0023] Etching double grooves on the surface of the laser unit to form a ridge waveguide structure, wherein the etching depth of the double grooves exceeds the active layer;

[0024] A groove is etched on the front cavity surface of the laser unit, and the etching depth exceeds the active layer.

[0025] Optionally, the method further includes:

[0026] Depositing an insulating passivation layer on the surface of the upper waveguide layer, and etching an electric injection window on the insulating passivation layer at a position corresponding to the ridge waveguide structure;

[0027] Vapor-depositing a front electrode layer on the surface of the insulating passivation layer;

[0028] A back metal electrode layer is evaporated on a side of the substrate facing away from the lower waveguide layer.

[0029] Optionally, the width of the double groove is 15 μm, the width of the ridge waveguide is 8 μm, and the width of the groove is 20 μm.

[0030] The implementation of the above scheme has the following beneficial effects: (1) By etching a groove on the front cavity surface of the laser unit and filling the groove with semi-insulating InP with high thermal conductivity, a heat dissipation channel is provided for the cavity surface, thereby reducing the cavity surface temperature of the device and optimizing the heat dissipation effect at the cavity surface of the device. (2) After the laser beam diverges through the semi-insulating InP area, the optical power density at the cavity surface is greatly reduced. (3) The electro-optical conversion gain at the cavity surface is removed, so that no heat is generated near the cavity surface. Based on the above three points, the cavity surface characteristics of the high-power long-wave infrared quantum cascade laser are greatly improved, which can greatly improve the output power and device reliability.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the figures are used to represent similar components, among which:

[0033] Figure 1 It is a schematic diagram of the three-dimensional structure of a high-power long-wave infrared quantum cascade laser provided in an embodiment of the present disclosure.

[0034] Figure 2 It is a preparation flow chart of a high-power long-wave infrared quantum cascade laser provided in an embodiment of the present disclosure.

[0035] In the figure: 1 substrate, 2 lower waveguide layer, 3 lower optical confinement layer, 4 active layer, 5 upper optical confinement layer, 6 upper waveguide layer, 7 filling material, 8 insulating passivation layer, 9 front electrode layer, 10 back electrode layer. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0039] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invention workpiece is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0040] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0042] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0043] The present disclosure provides a high-power long-wave infrared quantum cascade laser. Figure 1 The laser includes a laser unit, a trench structure, a filling material 7, an insulating passivation layer 8, a front electrode layer 9 and a back electrode layer 10.

[0044] The laser unit includes a substrate 1, a lower waveguide layer 2, a lower optical confinement layer 3, an active layer 4, an upper optical confinement layer 5 and an upper waveguide layer 6 which are stacked in sequence.

[0045] The groove structure is formed by etching the laser unit, including a groove located at the front end cavity surface of the laser unit and a double groove located between the grooves, and the double groove and the groove both extend from the upper waveguide layer 6 toward the substrate 1 and pass through the active layer 4. A ridge waveguide structure is formed between the double grooves. In a possible implementation, the width of the double groove is 15 μm, the width of the ridge waveguide is 8 μm, and the width of the groove is 20 μm.

[0046] The filling material 7 is filled in the trench structure, and the filling material 7 includes semi-insulating InP. In a possible implementation, the filling material 7 is Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm.

[0047] The insulating passivation layer 8 is disposed on the upper waveguide layer 6; the front electrode layer 9 is disposed on the insulating passivation layer 8; and the back electrode layer 10 is disposed on the side of the substrate 1 facing away from the lower waveguide layer 2. An electric injection window is provided on the insulating passivation layer 8 at a position corresponding to the ridge waveguide structure.

[0048] This embodiment also provides a method for manufacturing a high-power long-wave infrared quantum cascade laser, see Figure 2 The method includes steps S201 to S211.

[0049] S201 , manufacturing a laser unit, including sequentially growing a lower waveguide layer 2 , a lower optical confinement layer 3 , an active layer 4 , an upper optical confinement layer 5 and an upper waveguide layer 6 on a substrate 1 .

[0050] S203, making a groove structure, including etching the laser unit to form a double groove and a groove, the groove is located at the front end cavity surface of the laser unit, the double groove is located between the grooves, and the double groove and the groove both extend from the upper waveguide layer 6 toward the substrate 1 and pass through the active layer 4.

[0051] In a possible implementation, the step of making the groove structure includes: etching a double groove on the surface of the laser unit to form a ridge waveguide structure, wherein the etching depth of the double groove exceeds the active layer 4; etching a groove on the front cavity surface of the laser unit, wherein the etching depth exceeds the active layer 4.

[0052] The width of the double groove is 15 μm, the width of the ridge waveguide is 8 μm, and the width of the groove is 20 μm.

[0053] S205, filling the trench structure with a filling material 7 including semi-insulating InP. In a possible implementation, the filling material 7 is Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm.

[0054] S207 , depositing an insulating passivation layer 8 on the surface of the upper waveguide layer 6 , and etching an electrical injection window on the insulating passivation layer 8 at a position corresponding to the ridge waveguide structure.

[0055] S209 , vapor-depositing a front electrode layer 9 on the surface of the insulating passivation layer 8 .

[0056] S211 , vapor-depositing a back metal electrode layer on a side of the substrate 1 facing away from the lower waveguide layer 2 . Specific embodiment:

[0058] This embodiment provides a 9 μm wavelength high-power quantum cascade laser, the cavity length of the laser is 6 mm, and the device includes:

[0059] Substrate 1, made of InP, n-type doping, doping concentration of 1 to 3×10 18 cm -3 , thickness is about 100μm, surface defect density is less than 500cm -2 ;

[0060] The lower waveguide layer 2 is provided on the upper surface of the substrate 1 and is made of InP, n-type doped, and the doping concentration is 2×10 16 cm -3 , thickness 4 μm;

[0061] The lower optical confinement layer 3 is provided on the upper surface of the lower waveguide layer 2 and is made of InGaAs, n-type doped, and the doping concentration is 1×10 16 cm -3 , thickness 300nm;

[0062] The active layer 4 is arranged on the upper surface of the lower optical confinement layer 3, and is made of InGaAs / InAlAs superlattice. The gain process is single phonon resonance combined with microstrip transport cascade, the period number is 45, and the total thickness is 2.6 μm.

[0063] The upper optical confinement layer 5 is disposed on the upper surface of the active layer 4 and is made of InGaAs, n-type doped, with a doping concentration of 1×10 16 cm -3 , thickness 400nm;

[0064] The upper waveguide layer 6 is provided on the upper surface of the upper optical confinement layer 5 and is made of InP, n-type doped, and the main doping concentration is 2×10 16 cm -3 , with a thickness of 4.5 μm, and the top layer includes a transition doping layer and a high doping layer, and the doping concentration of the transition doping layer is 1 to 5×10 17 cm -3 , thickness 500nm, high doping layer doping concentration higher than 5×10 18 cm -3 , thickness 1 μm;

[0065] The upper waveguide layer 6, the upper optical confinement layer 5, the active layer 4, the lower optical confinement layer 3, and the lower waveguide layer 2 constitute a laser unit. The laser unit is provided with a groove structure. The groove structure includes a groove located at the front end cavity surface of the laser unit and a double groove located between the grooves. Both the double groove and the groove extend from the upper waveguide layer 6 toward the substrate 1 and pass through the active layer. A ridge waveguide structure is formed between the double grooves. The double groove width is 15 μm, the ridge waveguide width is 8 μm, and the groove width is 20 μm.

[0066] The double trench and the groove are filled with a filling material 7, which is a Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm;

[0067] The insulating passivation layer 8 is provided on the upper surface of the upper waveguide layer 6, made of SiO2, with a thickness of 300nm, and has an electrical injection window opened just above the ridge cavity;

[0068] The front electrode layer 9 is provided on the upper surface of the insulating passivation layer 8, made of Au, 4 μm thick, and includes a 15 nm thick Ti infiltration layer;

[0069] The back electrode layer 10 is disposed on the upper surface of the front electrode layer 9 and is made of AuGeNi / Au. The AuGeNi layer has a thickness of 200 nm and the Au layer has a thickness of 500 nm.

[0070] The method for manufacturing the above-mentioned 9μm wavelength high-power quantum cascade laser comprises the following steps:

[0071] Step 1: using metal organic chemical vapor deposition (MOCVD) technology, sequentially growing a lower waveguide layer 2, a lower optical confinement layer 3, an active layer 4, an upper optical confinement layer 5 and an upper waveguide layer 6 on a substrate 1;

[0072] Step 2: etching a double groove by wet photolithography to form a ridge waveguide structure, the double groove width is 15 μm, the etching depth exceeds the active layer 4, and the ridge waveguide width is 8 μm;

[0073] Step 3: Use wet etching to etch a groove on the front cavity surface. The groove width is 20 μm and the etching depth exceeds the active layer 4. In this way, the length of the semi-insulating InP region at the front cavity surface of the device is 10 μm.

[0074] Step 4: epitaxially fill the trench with a material 7 by using MOCVD technology, wherein the filling material 7 is semi-insulating InP;

[0075] Step 5: Deposit a SiO2 insulating passivation layer 8 using plasma enhanced chemical vapor deposition (PECVD) technology, and etch an electrical injection window;

[0076] Step 6: Using electron beam evaporation and electroplating technology to evaporate the front metal electrode layer;

[0077] Step 7: Thin and polish the substrate 1, and use electron beam evaporation or thermal evaporation technology to evaporate a back metal electrode layer on the back side of the substrate 1 to complete the preparation.

[0078] Compared with conventional long-wave infrared quantum cascade lasers, the front-end output cavity surface of the embodiment of the present invention is all made of nearly 10μm semi-insulating InP material, whose thermal conductivity is much higher than that of the original active area material, especially the thermal conductivity in the vertical direction, thereby greatly improving the heat dissipation characteristics at the cavity surface and reducing the temperature of the cavity surface during operation.

[0079] After simulation calculation, for conventional devices with the same lateral structural parameters, the average area of ​​the light spot at the output cavity surface is about 12.8μm2. For the device in the embodiment of the present invention, when the length of the epitaxial semi-insulating InP:Fe region is 10μm, the light spot diverges after the semi-insulating InP:Fe region, and the area of ​​the light spot after divergence is about 630μm2. The power surface density at the device cavity surface is reduced by about 49 times. By extending the length of the semi-insulating InP:Fe region, the light spot is further diverged, and the power density can be further reduced.

[0080] Since 10μm at the cavity surface is semi-insulating InP, electrical injection cannot be achieved, and thus this area itself does not generate heat. All the heat comes from heat conduction in the electrical injection area and a small amount of optical absorption heat. Combined with the aforementioned improvement in heat dissipation characteristics and reduction in optical power density, when the high-power quantum cascade laser is working, the cavity surface temperature is 60K to 100K lower than that of conventional devices, thereby effectively avoiding the problem of cavity surface burning and improving the output optical power and device reliability of the high-power quantum cascade laser.

[0081] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A high-power long-wave infrared quantum cascade laser, characterized in that: include: A laser unit comprises a substrate, a lower waveguide layer, a lower optical confinement layer, an active layer, an upper optical confinement layer and an upper waveguide layer which are stacked in sequence; A groove structure is formed by etching the laser unit, including a groove located inside the front end cavity surface of the laser unit and extending along the cavity surface, and a double groove inside the groove, wherein the double groove and the groove both extend from the upper waveguide layer toward the substrate and pass through the active layer, and a ridge waveguide structure is formed between the double grooves; A filling material is filled in the trench structure, wherein the filling material includes semi-insulating InP.

2. The high-power long-wave infrared quantum cascade laser according to claim 1, characterized in that: The filling material is Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm.

3. The high-power long-wave infrared quantum cascade laser according to claim 1, characterized in that: The laser also includes: an insulating passivation layer, disposed on the upper waveguide layer; A front electrode layer, provided on the insulating passivation layer; The back electrode layer is arranged on a side of the substrate facing away from the lower waveguide layer.

4. The high-power long-wave infrared quantum cascade laser according to claim 3, characterized in that: A ridge waveguide structure is formed between the double grooves, and an electric injection window is opened on the insulating passivation layer at a position corresponding to the ridge waveguide structure.

5. The high-power long-wave infrared quantum cascade laser according to claim 4, characterized in that: The width of the double groove is 15 μm, the width of the ridge waveguide structure is 8 μm, and the width of the groove is 20 μm.

6. A method for manufacturing a high-power long-wave infrared quantum cascade laser, characterized in that: include: Fabricating a laser unit, including sequentially growing a lower waveguide layer, a lower optical confinement layer, an active layer, an upper optical confinement layer, and an upper waveguide layer on a substrate; Manufacturing a groove structure, including etching a laser unit to form a groove located inside a front end cavity surface of the laser unit and extending along the cavity surface and a double groove inside the groove, wherein the double groove and the groove both extend from the upper waveguide layer toward the substrate and pass through the active layer, and a ridge waveguide structure is formed between the double grooves; A filling material including semi-insulating InP is filled in the trench structure.

7. The method for manufacturing a high-power long-wave infrared quantum cascade laser according to claim 6, characterized in that: The filling material is Fe-doped semi-insulating InP with a resistivity higher than 10 8 Ω·cm.

8. The method for manufacturing a high-power long-wave infrared quantum cascade laser according to claim 6, characterized in that: The steps of making the groove structure include: Etching double grooves on the surface of the laser unit to form a ridge waveguide structure, wherein the etching depth of the double grooves exceeds the active layer; A groove is etched on the front cavity surface of the laser unit, and the etching depth exceeds the active layer.

9. The method for manufacturing a high-power long-wave infrared quantum cascade laser according to claim 8, characterized in that: The method further comprises: Depositing an insulating passivation layer on the surface of the upper waveguide layer, and etching an electric injection window on the insulating passivation layer at a position corresponding to the ridge waveguide structure; Vapor-depositing a front electrode layer on the surface of the insulating passivation layer; A back metal electrode layer is evaporated on a side of the substrate facing away from the lower waveguide layer.

10. The method for manufacturing a high-power long-wave infrared quantum cascade laser according to claim 8, characterized in that: The width of the double groove is 15 μm, the width of the ridge waveguide structure is 8 μm, and the width of the groove is 20 μm.

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