CN105610047A - GeSn multi-quantum well metal cavity laser and fabrication method thereof - Google Patents

Abstract

The invention discloses a GeSn multi-quantum well metal cavity laser, which comprises a Si substrate, a Ge buffer layer, a lower distributed Bragg reflector, an active layer, an upper distributed Bragg reflector and an Si substrate arranged from bottom to top. The Ge _0.88 Sn _0.12 buffer layer, the active layer adopts the strain compensation quantum well structure, the Ge _0.88 Sn _0.12 buffer layer, the upper distributed Bragg reflector, the active layer and the lower distributed Bragg reflector are etched into a cylindrical mesa, and the cylindrical mesa A silicon nitride film is grown on the side surface and the surface of the lower distributed Bragg reflector, and the Ge _0.88 Sn _0.12 buffer layer and the surface of the silicon nitride film are coated with an Ag metal layer. The invention can not only be compatible with the CMOS process, but also can change the stress by adjusting the size of the Sn component to realize the requirements of the germanium-tin light source for light of different wavelengths, has high photoelectric conversion efficiency and light stability, and is simple and convenient to process.

Description

GeSn multi-quantum well metal cavity laser and its manufacturing method

technical field

The invention belongs to the technical field of semiconductor optoelectronics, in particular to a GeSn multi-quantum well metal cavity laser and a manufacturing method thereof.

Background technique

Si-based semiconductor is the cornerstone of the modern microelectronics industry, and Si's complementary metal oxide semiconductor (complementarymentaloxidesemiconductor, CMOS) process technology has formed a powerful microelectronics industry. With the advancement of technology, the integration level of Si-based integrated circuits is getting higher and higher, and the performance is getting better and better. However, with the continuous improvement of integration and the reduction of device feature size, a series of problems also arise, such as serious heat dissipation problems, high power consumption of electrical interconnection, RC delay leads to limited electrical interconnection speed, quantum Restriction effects, etc., all restrict the further development of integrated circuits. Si-based optoelectronics (siliconphotonics), which aims to realize Si-based optoelectronic integrated circuit (OEIC), is expected to solve this problem. Unfortunately, Si itself does not have good optical properties, and has its own inherent defects in photoelectric conversion, electro-optic modulation, electro-optic conversion, etc., such as low carrier mobility, highly symmetric structure, zero linear electro-optic coefficient, indirect Band gap material, low luminous efficiency. However, over the past ten years, through the joint efforts of scientists, Si-based photonics has made great progress, and the preparation of various Si-based photonics materials and devices have made gratifying breakthroughs. At present, in addition to Si-based light sources, people have mature applications in the fields of Si-based photodetectors, electro-optic modulators, and wavelength division multiplexers/demultiplexers. Therefore, efficient Si-based light sources, especially Si-based lasers, have become the most challenging and important goal in Si-based OEIC.

At present, there is no mature and effective solution for Si-based light sources. To realize the Si material itself as a light source, it is necessary to suppress non-radiative recombination and increase the probability of radiative recombination through material modification, energy band engineering and other methods, such as Si dislocation ring luminescence, Si Raman laser, doping rare earth ions and other methods. However, these methods are either complex in process, poor in repeatability stability, or optical pumping operation, which makes little contribution to Si-based optical interconnection, and further innovation is needed. In addition, III-V materials with good luminescence properties can be integrated on Si to achieve Si-based high-efficiency luminescence. However, the process of the III-V family is poorly compatible with the SiCMOS process, so it is not conducive to OEIC.

Germanium-tin alloy is a group IV semiconductor material that has received the most attention in recent years. It is the only group IV binary alloy semiconductor with a direct band gap, which makes it of great research significance in silicon electronics, especially Si-based high-efficiency light sources, and has become a new research hotspot in recent years. Although the GeSn alloy has an indirect band gap when the Sn content is relatively low (<10%), the GeSn alloy with a low Sn composition also has important research significance. GeSn alloy has a larger absorption coefficient than Ge, and the introduction of Sn will redshift the absorption edge, and it is also a narrow band gap material, and the band gap is adjustable between 0 and 0.66eV. The band gap of germanium-tin alloy decreases with the increase of Sn content, and its optical absorption edge gradually redshifts. The results of D'Costa et al. show that even if the Sn content is only 0.02, germanium-tin alloy is sufficient to cover the entire communication band, and in this The absorption coefficient of the wavelength band is at least 10 times higher than that of Ge, and it is expected to be used in infrared optoelectronic devices and in the fields of infrared detection and imaging. Compared with traditional infrared optoelectronic materials (such as HgCdTe), Ge _1-x Sn _x alloy has the advantages of non-toxicity and pollution-free, and it is also compatible with silicon microelectronics process and easy to integrate. Therefore, Ge _1-x Sn _x alloys are of great significance in the development of infrared optoelectronics. In addition, germanium-tin alloy has large electron and hole mobility and can be used to make high-performance microelectronic devices, which makes this material suitable as a high-speed CMOS channel material.

At present, the research on lasers based on germanium-tin materials is still in its infancy. Lasers based on germanium-tin materials published at home and abroad still have shortcomings such as low photoelectric conversion efficiency and poor photostability, and can only be realized by pulsed light pumping at present. For lasing, a suitable electrical pumping method has yet to be found; the critical temperature of GeSn alloy lasing is low, and there is still a certain distance from the application at room temperature.

Contents of the invention

The object of the present invention is to provide a GeSn multi-quantum well metal cavity laser and its manufacturing method, aiming to solve the shortcomings of metal cavity laser devices using III-V materials in the prior art that have poor heat dissipation and poor photostability. It cannot meet the requirements of the on-chip optoelectronic integrated system for the light source, and the germanium-tin laser is difficult to realize the problem of room temperature electrical injection.

The present invention is achieved like this, a kind of GeSn multiple quantum well metal cavity laser, comprises Si substrate, and the Ge buffer layer that is arranged on Si substrate from bottom to top, lower distribution Bragg reflector, active layer, upper distribution Bragg reflector and Ge _0.88 Sn _0.12 buffer layer, the active layer adopts strain compensation quantum well structure, the Ge _0.88 Sn _0.12 buffer layer, upper distributed Bragg reflector, active layer and lower distributed Bragg reflector are etched into A silicon nitride film is grown on the surface of the cylindrical mesa, the side of the cylindrical mesa and the surface of the lower distributed Bragg reflector, and the Ge _0.88 Sn _0.12 buffer layer and the surface of the silicon nitride film are coated with an Ag metal layer.

The present invention is also characterized in that the active layer is composed of 12 layers of GeSn potential wells with compressive strain and corresponding 13 layers of SiGeSn potential barriers with tensile strain.

The present invention is also characterized in that the lower distributed Bragg reflector is an n-type distributed Bragg reflector composed of 24.5 pairs of Si _a Ge _b Sn _c / _{Six Ge y Sn z} materials alternately, and the upper distributed Bragg reflector is composed of 8.5 A p-type distributed Bragg reflector composed of alternating pairs of Si _a Ge _b Sn _c / _{Six Ge y Sn z} materials, the optical thickness of each layer of material is 1/4 of the central reflection wavelength, where a+b+c=1 , 0<a<0.1, 0<b<0.8, 0<c<0.3, x+y+z=1, 0<x<0.8, 0<y<0.12, 0<z<0.3.

The present invention is also characterized in that the etching depth of the cylindrical mesa reaches to the upper end of the lower distributed Bragg reflector, the height of the cylindrical mesa is 3.5 μm, and the radius of the cylindrical mesa is 1 μm.

The manufacturing method of above-mentioned GeSn multiple quantum well metal cavity laser comprises the following steps:

Step 1, using low temperature molecular beam epitaxy to grow a Ge thin film on the Si substrate as a Ge buffer layer;

Step 2, sequentially growing a lower distributed Bragg reflector, an active layer, an upper distributed Bragg reflector and a strain-relaxed Ge _0.88 Sn _0.12 buffer layer on the Ge buffer layer;

Step 3, etching the lower distributed Bragg reflector, the active layer, the upper distributed Bragg reflector and the strain relaxation Ge _0.88 Sn _0.12 buffer layer obtained in step 2 into a cylindrical mesa;

Step 4, using low-pressure chemical vapor deposition to grow a silicon nitride film on the side of the cylindrical table and the surface of the lower distributed Bragg mirror;

Step 5, coating Ag on the surface of the Ge _0.88 Sn _0.12 buffer layer and the silicon nitride film to form an Ag metal layer.

The beneficial effects of the present invention are as follows:

Aiming at the shortcomings of metal cavity laser devices using III-V materials in the prior art, such as poor heat dissipation and poor light stability, and still unable to meet the requirements of on-chip photoelectric integration systems for light sources, the invention proposes a columnar laser device with a metal cavity. A laser device with a GeSn multiple quantum well structure and a fabrication method thereof. The invention can not only be compatible with the CMOS process, but also can change the stress by adjusting the size of the Sn component to realize the requirements of the germanium-tin light source for light of different wavelengths, has high photoelectric conversion efficiency and light stability, and is simple and convenient to process.

Description of drawings

Fig. 1 is the structural representation of GeSn multiple quantum well metal cavity laser of the embodiment of the present invention;

Fig. 2 is the processing schematic diagram of step 1 in the manufacturing method of GeSn multi-quantum well metal cavity laser of the embodiment of the present invention;

Fig. 3 is the processing schematic diagram of step 2 in the manufacturing method of GeSn multiple quantum well metal cavity laser of the embodiment of the present invention;

Fig. 4 is the processing schematic diagram of step 3 in the manufacturing method of GeSn multi-quantum well metal cavity laser of the embodiment of the present invention;

Fig. 5 is the processing schematic diagram of step 4 in the manufacturing method of GeSn multiple quantum well metal cavity laser of the embodiment of the present invention;

Fig. 6 is the processing schematic diagram of step 5 in the manufacturing method of GeSn multi-quantum well metal cavity laser of the embodiment of the present invention;

In the figure: 1. Si substrate; 2. Ge buffer layer; 3. Lower distributed Bragg reflector; 4. Active layer; 5. Upper distributed Bragg reflector; 6. Ge _0.88 Sn _0.12 buffer layer; 7. Nitriding Silicon film, 8, Ag metal layer.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Fig. 1 shows the structure of a GeSn multi-quantum well metal cavity laser provided by an embodiment of the present invention. As shown in Figure 1, a kind of GeSn multiple quantum well metal cavity laser of the embodiment of the present invention, comprises Si substrate 1, and the Ge buffer layer 2 that is arranged on Si substrate 1 from bottom to top, lower distributed Bragg reflector 3. Active layer 4, upper distributed Bragg reflector 5 and Ge _0.88 Sn _0.12 buffer layer 6, active layer 4 adopts strain compensation quantum well structure, Ge _0.88 Sn _0.12 buffer layer 6, upper distributed Bragg reflector 5, active Layer 4 and the lower distributed Bragg reflector 3 are etched into a cylindrical mesa, and a silicon nitride film 7, a Ge _0.88 Sn _0.12 buffer layer 6 and a silicon nitride film 7 are grown on the side of the cylindrical mesa and the surface of the lower distributed Bragg reflector 3 The surface is coated with an Ag metal layer 8 . Since silver has high thermal conductivity and reflectivity, using Ag metal as a metal cavity is more conducive to heat dissipation and has better light reflectivity, which is more beneficial to forming laser light.

In the embodiment of the present invention, the active layer 4 is composed of 12 layers of compressively strained GeSn potential wells and corresponding 13 layers of tensile strained SiGeSn barriers. The quantum well structure can effectively confine the carriers, improve the carrier injection and luminous efficiency of the material, and a reasonable SiGeSn/GeSn/SiGeSn multiple quantum well structure is conducive to the realization of high-efficiency luminescence.

In the embodiment of the present invention, the lower distributed Bragg reflector 3 is an n-type distributed Bragg reflector composed of 24.5 pairs of Si _a Ge _b Sn _c / _{Six Ge y Sn z} materials alternately, and the upper distributed Bragg reflector 5 is composed of 8.5 A p-type distributed Bragg reflector composed of alternating pairs of Si _a Ge _b Sn _c / _{Six Ge y Sn z} materials, the optical thickness of each layer of material is 1/4 of the central reflection wavelength, where a+b+c=1 , 0<a<0.1, 0<b<0.8, 0<c<0.3, x+y+z=1, 0<x<0.8, 0<y<0.12, 0<z<0.3. Since the electromagnetic wave whose frequency falls within the energy gap range cannot penetrate, the reflectivity of the Bragg reflector can reach more than 99%. At the same time, the structure does not have the absorption problem of the metal mirror, and the position of the energy gap can be adjusted by changing the refractive index or thickness of the material.

In the embodiment of the present invention, the etching depth of the cylindrical mesa reaches to the upper end of the lower DBR, the height of the cylindrical mesa is 3.5 μm, and the radius of the cylindrical mesa is 1 μm.

The manufacturing method of the above-mentioned GeSn multi-quantum well metal cavity laser can be carried out in the manner shown in Fig. 2-Fig. 6, and specifically includes the following steps:

Step 1, utilize low-temperature molecular beam epitaxy to grow a layer of Ge thin film on Si substrate, as Ge buffer layer, the thickness of Ge buffer layer is 240nm; In the embodiment of the present invention, adopt low, high temperature two-step method, first in After growing a low-temperature germanium buffer layer on the Si substrate at 250°C, the temperature is raised to 500°C to grow a high-temperature germanium buffer layer.

Step 2, growing a lower distributed Bragg reflector, an active layer, an upper distributed Bragg reflector and a strain-relaxed Ge _0.88 Sn _0.12 buffer layer in sequence on the Ge buffer layer.

Step 3. Etching the lower distributed Bragg reflector, the active layer, the upper distributed Bragg reflector and the strain relaxation Ge _0.88 Sn _0.12 buffer layer obtained in step 2 into a cylindrical mesa.

Step 4, growing a silicon nitride film on the side of the cylindrical table and the surface of the lower distributed Bragg mirror by using a low-pressure chemical vapor deposition method.

Step 5, coating Ag on the surface of the Ge _0.88 Sn _0.12 buffer layer and the silicon nitride film to form an Ag metal layer.

In the embodiment of the present invention, the upper and lower distributed Bragg reflectors in step 2 are composed of two materials with different refractive indices arranged alternately in the form of Si _a Ge _b Sn _c / _{Six Ge y Sn z} (ABAB) The periodic structure, the optical thickness of each layer of material is 1/4 of the central reflection wavelength.

In the embodiment of the present invention, the active layer in step 2 is 25 layers of multi-quantum wells, that is, 12 layers of GeSn potential wells with compressive strain and 13 layers of SiGeSn potential barriers with tensile strain, and the thickness of each layer of potential wells is 6nm. The thickness of the layer barrier is 8 nm. Based on the condition of strain balance, it minimizes the total strain energy, thereby reducing the strain-mismatched dislocation density in the multi-quantum well (MQWs) region; in addition, the use of MQWs structure can offset the image transmission and metal loss, so as to obtain a large enough optical gain.

In the embodiment of the present invention, the growth method of the strain-relaxed Ge _0.88 Sn _0.12 buffer layer in step 2 adopts the low-temperature molecular beam epitaxy method, the growth temperature is 200° C., and the thickness is 300 nm.

In the embodiment of the present invention, the etching method in step 3 is: use a silicon nitride (Si ₃ N ₄ ) circular mask to determine the photolithography area, and use inductively coupled plasma/reactive ion etching (PE/RIE ) method to form pillars, and then etch away Si ₃ N ₄ as a mask, wherein the silicon nitride film is a high-stress film suitable for strained GeSn devices, and is used as a mask for protecting patterns during anisotropic etching . The circular mask is grown by LPCVD (low pressure chemical vapor deposition) under the condition of low pressure and 700°C, with a radius of 1 μm. The etchant used for ion etching in step 3 can be a mixed solution of potassium hydroxide and isopropanol, the formula is potassium hydroxide: isopropanol: water = 1:2:2, the etching temperature is 80°C, and the etching time After about 90 minutes, the height of the formed pillars is 3.5 μm; the Si ₃ N ₄ used as a mask is etched with a mixed solution of hydrofluoric acid and phosphoric acid at 180° C.

In the embodiment of the present invention, the growth of the silicon nitride film in step 4 adopts a low-pressure chemical vapor deposition method. The thickness of the silicon nitride film in step 4 is 10 nm.

In the embodiment of the present invention, the Ag metal layer coated in step 5 is columnar and manufactured by a metal evaporation process with a deposition rate of 0.18 nm/s.

The Ge thin film grown in this embodiment is used as a buffer layer for growing GeSn alloy in subsequent steps, which can reduce epitaxy mismatch and improve the quality of GeSn alloy. The distributed Bragg reflectors (DBRs) are part of the optical microcavity, which is composed of two materials with different refractive indices arranged alternately in the form of Si _a Ge _b Sn _c / _{Six Ge y Sn z} (ABAB) structure, the optical thickness of each layer of material is 1/4 of the central reflection wavelength. Since the electromagnetic wave whose frequency falls within the energy gap range cannot penetrate, the reflectivity of the Bragg reflector can reach more than 99%. At the same time, the structure does not have the absorption problem of the metal mirror, and the position of the energy gap can be adjusted by changing the refractive index or thickness of the material. The multi-quantum well medium alternately grown by GeSn/SiGeSn is used as the active region, the compressive stress is introduced into the GeSn material, and the tensile strain is introduced into the SiGeSn to increase the optical gain of the active region so as to improve the luminous efficiency of the metal cavity laser device. In addition, by adjusting the size of the Sn component, the stress of each layer can be adjusted according to the requirements, the photoelectric conversion efficiency can be improved, and the GeSn/SiGeSn multi-quantum well laser device with a specific light wavelength can be prepared. Since silver has high thermal conductivity and reflectivity, using Ag metal as a metal cavity is more conducive to heat dissipation and has better light reflectivity, which is more beneficial to forming laser light.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (5)

1. a GeSn MQW wire chamber laser instrument, is characterized in that, comprise Si substrate and fromLower and on be arranged on the Ge cushion on Si substrate, lower distribution Bragg reflector, active layer, upper distributionBragg mirror and Ge_0.88Sn_0.12Cushion, described active layer adopts strain-compensated quantum well structure, instituteState Ge_0.88Sn_0.12Cushion, upper distribution Bragg reflector, active layer and lower distribution Bragg reflector are carvedLose into cylindrical mesa, the side of cylindrical mesa and lower distribution Bragg reflector superficial growth have nitrogenizeSilicon thin film, described Ge_0.88Sn_0.12On cushion and silicon nitride mask surface, scribble Ag metal level.

2. GeSn MQW wire chamber laser instrument as claimed in claim 1, is characterized in that, described inActive layer is made up of GeSn potential well and 13 layers of corresponding tensile strain SiGeSn potential barrier of 12 lamination strains.

3. GeSn MQW wire chamber laser instrument as claimed in claim 1, is characterized in that, described inLower distribution Bragg reflector is by 24.5 couples of Si_aGe_bSn_c/Si_xGe_ySn_zThe material alternately N-shaped of composition distributesFormula Bragg mirror, described upper distribution Bragg reflector is by 8.5 couples of Si_aGe_bSn_c/Si_xGe_ySn_zMaterialThe p-type distributed bragg reflector mirror of composition alternately, reflection wavelength centered by the optical thickness of every layer material1/4, wherein a+b+c=1,0 < a < 0.1,0 < b < 0.8,0 < c < 0.3, x+y+z=1,0 < x < 0.8,0 < y < 0.120＜z＜0.3。

4. GeSn MQW wire chamber laser instrument as claimed in claim 1, is characterized in that, described inThe etching depth of cylindrical mesa is until lower distribution Bragg reflector upper end, and the height of cylindrical mesa is3.5 μ m, the radius of cylindrical mesa is 1 μ m.

5. the preparation method of GeSn MQW wire chamber laser instrument as described in as arbitrary in claim 1-4, itsBe characterised in that, comprise the steps:

Step 1, on Si substrate, utilize low temperature molecular beam epitaxy method growth one deck Ge film, slow as GePunching layer;

Step 2, on Ge cushion successively distribution Bragg reflector, active layer under growth, on the cloth that distributesGlug speculum and deformation relaxation Ge_0.88Sn_0.12Cushion;

Step 3, the lower distribution Bragg reflector that step 2 is obtained, active layer, upper distribution bragg are anti-Penetrate mirror and deformation relaxation Ge_0.88Sn_0.12Cushion is etched into cylindrical mesa;

Step 4, utilize low pressure chemical on side and the lower distribution Bragg reflector surface of cylindrical mesaVapour deposition process grown silicon nitride film;

Step 5, at Ge_0.88Sn_0.12Cushion and silicon nitride film surface are coated with Ag, form Ag metal level.