A ten-stage multiplier avalanche photodiode based on SAGCM structure

Abstract

The embodiment of the present application provides a ten-stage multiplication avalanche photodiode based on the SAGCM structure. The diode is a SAGCM structure, and includes an ohmic contact layer, a P-type barrier layer, an absorption layer, a transition layer, a charge layer, a multiplication layer, an N-type barrier layer and a substrate from top to bottom. The absorption layer performs photoelectric conversion to increase light absorption. The transition layer smoothes the band gap between the absorption layer and the charge layer to reduce the hole accumulation effect. The charge layer adjusts the electric field so that the absorption area is kept at a low electric field and the multiplication area is kept at a high electric field. The multiplication layer enhances electron impact ionization and suppresses hole impact ionization. By optimizing the doping concentration and thickness of the multiplication layer and the charge layer, the electric field and current characteristics can be effectively adjusted to achieve low noise and high gain performance of the device.

Description

Technical Field

[0001] The present application relates to the field of semiconductor design and manufacturing technology, and in particular to a ten-stage multiplication avalanche photodiode based on a SAGCM structure. Background Art

[0002] Avalanche Photodiode (APD) exhibits higher sensitivity and photoelectric gain than PIN photodiode due to its internal current amplification mechanism, and can effectively detect extremely low-intensity light signals and even single photons, which makes APD perform well in photodetection applications. However, the traditional single-stage multiplication APD faces a significant technical challenge when operating in linear mode, namely the trade-off between gain and excess noise. As the APD gain increases, the randomness of impact ionization increases, resulting in an increase in excess noise level, which limits the application potential of APD in the field of high-performance photodetection.

[0003] In order to solve this problem, researchers have proposed the impact ionization engineering (Impact Ionization Engineering, I 2 E) concept, by precisely controlling the electric field distribution in the multiplication region, the impact ionization process is more concentrated in a specific area, thereby effectively reducing excess noise. Although this method can improve the performance of APD to a certain extent, the overall gain of the device may be affected due to the reduction of the impact ionization area.

[0004] Therefore, how to develop a technical solution that can maintain or improve APD gain and effectively reduce excess noise has become an important direction in current near-infrared APD research. Summary of the invention

[0005] The present application provides a ten-stage avalanche photodiode based on a SAGCM structure, which can effectively adjust the electric field and current characteristics by optimizing the doping concentration and thickness of the multiplication layer and the charge layer to achieve low noise and high gain performance of the device.

[0006] In order to achieve the above purpose, the technical solution adopted in the embodiment of the present application is as follows:

[0007] In a first aspect, an embodiment of the present application provides a ten-stage multiplication avalanche photodiode based on a SAGCM structure, wherein the diode is a SAGCM structure, and includes, from top to bottom, an ohmic contact layer, a P-type barrier layer, an absorption layer, a transition layer, a charge layer, a multiplication layer, an N-type barrier layer, and a substrate;

[0008] An absorption layer, used for photoelectric conversion and increasing light absorption;

[0009] The transition layer is used to smooth the band gap between the absorption layer and the charge layer and reduce the hole accumulation effect;

[0010] A charge layer for adjusting the electric field so that the absorption region is kept at a low electric field and the multiplication region is kept at a high electric field;

[0011] The multiplication layer is used to enhance electron impact ionization and suppress hole impact ionization.

[0012] In a possible embodiment, the multiplication layer includes a plurality of multiplication units, and each multiplication unit includes a preheating layer, a buffer layer, an impact ionization layer, an electron cooling layer, and a relaxation layer.

[0013] In a possible embodiment, the impact ionization layer uses lattice-matched InAlAs and InGaAs materials, and the band gap is adjusted by controlling the Al and Ga components as the avalanche multiplication material of the multiplication region.

[0014] In a possible embodiment, the absorption layer is made of In 1-x Ga x As material, the band gap is adjusted by adjusting the composition of In and Ga.

[0015] In a possible embodiment, the charge layer is made of InAlAs material, and the electric field is controlled by adjusting the thickness and doping concentration.

[0016] In a possible embodiment, the material selected for the substrate is InP.

[0017] In a possible embodiment, the N-type barrier layer includes a first InAlAs layer and a second InAlAs layer.

[0018] The above-mentioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application; and in the present application, (non-conflicting options) options and other options can also be freely combined. After understanding the scheme of the present application, those skilled in the art can understand that there are multiple combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here.

[0019] Compared with the prior art, the embodiment of the present application proposes a ten-stage multiplication avalanche photodiode based on the SAGCM structure. The diode is a SAGCM structure, and includes an ohmic contact layer, a P-type barrier layer, an absorption layer, a transition layer, a charge layer, a multiplication layer, an N-type barrier layer and a substrate from top to bottom. The absorption layer performs photoelectric conversion to increase light absorption. The transition layer smoothes the band gap between the absorption layer and the charge layer to reduce the hole accumulation effect. The charge layer adjusts the electric field so that the absorption area is kept at a low electric field and the multiplication area is kept at a high electric field. The multiplication layer enhances electron impact ionization and suppresses hole impact ionization. By optimizing the doping concentration and thickness of the multiplication layer and the charge layer, the electric field and current characteristics can be effectively adjusted to achieve low noise and high gain performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A schematic diagram showing a ten-stage multiplication avalanche photodiode based on a SAGCM structure proposed in an embodiment of the present application

[0022] Figure 2 A schematic diagram of the structure of the multiplication layer proposed in an embodiment of the present application is shown.

[0023] Figure 3 The electric field diagram after optimization of the ten-level APD structure proposed in the embodiment of the present application is shown.

[0024] Figure 4 The photocurrent, dark current and gain diagram of the optimized ten-level APD structure proposed in the embodiment of the present application are shown. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0027] It should be noted that, in the absence of conflict, the features in the embodiments of the present application may be combined with each other.

[0028] In the existing technology, how to develop a technical solution that can maintain or improve APD gain and effectively reduce excess noise has become an important direction in current near-infrared APD research.

[0029] Therefore, in order to solve the above-mentioned technical problems, the embodiment of the present application proposes a ten-stage multiplication avalanche photodiode based on the SAGCM structure, which is particularly suitable for short-wave infrared detection in the semiconductor field in order to achieve low noise and high gain performance. The overall structure of the device follows the SAGCM (separation absorption, transition, charge and multiplication) design principle, and the specific layers are ohmic contact layer, P-type barrier layer, absorption layer, transition layer, charge layer, multiplication layer, N-type barrier layer and substrate from top to bottom. The multiplication layer is a key part, which is composed of a plurality of repeated multiplication units, each of which includes an electron preheating layer, a buffer layer, a collision ionization layer and an electron relaxation layer. The design of these layers enables photogenerated electrons to undergo avalanche multiplication when passing through, thereby greatly increasing the output current. By precisely controlling the doping concentration and thickness of the electron cooling layer and the charge layer in the multiplication layer, the electric field distribution is optimized, thereby effectively reducing noise and increasing gain, which will be further described in detail below.

[0030] Please refer to Figure 1 , Figure 1 A schematic diagram of a ten-stage multiplication avalanche photodiode based on a SAGCM structure proposed in an embodiment of the present application is shown. The diode is a SAGCM (Separated Absorption, Grading, Charge and Multiplication) structure, which includes an ohmic contact layer, a P-type barrier layer, an absorption layer, a transition layer, a charge layer, a multiplication layer, an N-type barrier layer and a substrate from top to bottom;

[0031] An absorption layer, used for photoelectric conversion and increasing light absorption;

[0032] The transition layer is used to smooth the band gap between the absorption layer and the charge layer and reduce the hole accumulation effect;

[0033] A charge layer for adjusting the electric field so that the absorption region is kept at a low electric field and the multiplication region is kept at a high electric field;

[0034] The multiplication layer is used to enhance electron impact ionization and suppress hole impact ionization.

[0035] The ten-stage multiplication avalanche photodiode in this application is designed for short-wave infrared detection, and has the characteristics of high gain and low noise. The material used for the ohmic contact layer is InGaAs, which can provide good electrical contact and ensure that the current flows smoothly into the device. The material of the P-type barrier layer is InAlAs, which can prevent electrons from penetrating directly from the top to the absorption layer, ensuring that the photogenerated electrons are effectively absorbed in the absorption layer. The material of the absorption layer is InGaAs, which can perform photoelectric conversion, convert incident photons into electron-hole pairs, and increase light absorption. The material of the transition layer is InAlGaAs, which can smooth the band gap between the absorption layer and the charge layer, reduce the hole accumulation effect, reduce the influence of the interface state, and improve the device performance. The material of the charge layer is InAlAs, which can adjust the electric field distribution, keep the absorption zone at a low electric field, and keep the multiplication zone at a high electric field, thereby optimizing the electric field distribution and improving the device performance. The material of the multiplication layer is InAlGaAs, which can enhance electron impact ionization and suppress hole impact ionization through multiple sublayers (electron preheating layer, buffer layer, impact ionization layer, electron relaxation layer), achieving the purpose of approximate single electron multiplication, thereby improving gain and reducing noise. The material of the N-type barrier layer is InAlAs, which can prevent electrons from penetrating directly from the multiplication layer to the bottom, ensuring that the electrons are fully multiplied in the multiplication layer. The material of the substrate is InP, which can provide mechanical support and electrical insulation to ensure stable operation of the device.

[0036] The working principle of the ten-stage multiplication avalanche photodiode in this application is as follows: the ohmic contact layer is connected to a negative voltage, the InP substrate is added with a positive voltage, the entire device is in a reverse biased state, and then light is irradiated from the top ohmic contact layer, through the InAlGaAs and InAlAs layers in the P-type barrier layer, and enters the InGaAs absorption layer, and then the absorption layer absorbs photons to complete the photoelectric conversion and form electron-hole pairs. Under the action of the built-in electric field, electrons drift to the N region, and holes drift to the P region. The photogenerated electrons finally reach the multiplication layer via the transition layer and the charge layer. In the multiplication layer, electrons collide with the lattice to produce new electron-hole pairs, and these carriers continue to cause new collision ionization, resulting in avalanche multiplication of carriers and obtaining current gain.

[0037] The doping concentration and thickness in the charge layer are optimized to ensure that the electric field is properly distributed between the absorption and multiplication regions, improving device performance. The doping concentration and thickness in the electron cooling layer are optimized to ensure that the electrons can be effectively cooled during the multiplication process, reducing thermal noise.

[0038] Through this optimized design, the ten-stage avalanche photodiode significantly reduces noise and improves overall performance while maintaining high gain.

[0039] The multiplication layer includes a plurality of multiplication units, and each multiplication unit includes a preheating layer, a buffer layer, an impact ionization layer, an electron cooling layer, and a relaxation layer.

[0040] Figure 2 The schematic diagram of the structure of the multiplication layer proposed in the embodiment of the present application is shown, which is composed of 76 thin layers, multiplied 10 times in total, and the doping concentration of the electron cooling layer is 7×10 17 cm -3 The impact ionization layer uses InAlGaAs material with a low threshold energy. When electrons enter the impact ionization layer from the InAlAs buffer layer with a high threshold energy, they will obtain part of the conduction band step energy due to the difference in threshold energy, further increasing the impact ionization rate of electrons. High gain is achieved through multi-stage multiplication, and thermal noise is reduced through the electron cooling layer.

[0041] After multiple multiplication units are connected in series, the electrons in each unit gradually accumulate gain after undergoing the process of preheating, collision ionization, cooling and relaxation. This multi-stage multiplication design can achieve very high gain while maintaining a low noise level. The electric field distribution inside each multiplication unit is carefully designed to ensure smooth transmission of electrons between layers and avoid electrical breakdown caused by sudden changes in the electric field. Through the design of the electron cooling layer and the relaxation layer, the energy of the electrons is effectively managed, thermal noise is reduced, and the overall performance of the device is improved.

[0042] The material of the ohmic contact layer is InGaAs, with a doping concentration of 4×10 19 cm -3 , thickness 15-30nm. It can provide good electrical contact and ensure that the current flows out of the device smoothly.

[0043] The impact ionization layer uses lattice-matched InAlAs and InGaAs materials, and the band gap is adjusted by controlling the Al and Ga components as the avalanche multiplication material in the multiplication zone.

[0044] The impact ionization layer can adjust the band gap by controlling the composition of Al and Ga, making it suitable as an avalanche multiplication material in the multiplication zone. The band gap adjustment is achieved by changing the ratio of Al and Ga to accurately control the band gap of the material, thereby optimizing the ionization efficiency during the avalanche multiplication process.

[0045] The absorption layer uses In 1-x Ga x As material, the band gap is adjusted by adjusting the composition of In and Ga.

[0046] The absorption layer consists of two layers of In 1-x Ga x As material composition, doping concentration is 1×10 18 cm -3 , 1×10 14 -1×1015 cm -3 The thickness ranges are 250±50nm and 1250±50nm respectively, and the total thickness is maintained at 1.5μm. It can perform photoelectric conversion, convert incident photons into electron-hole pairs, and increase light absorption.

[0047] The band gap of the absorption layer is adjusted by adjusting the composition of In and Ga. The band gap is adjusted by using x=0.47, so that the wavelength range of the absorption layer is concentrated in 0.8-1.8μm, which makes the device have high sensitivity in the short-wave infrared region.

[0048] The charge layer is made of InAlAs material, and the electric field is controlled by adjusting the thickness and doping concentration.

[0049] The charge layer is composed of two layers of InAlAs with different doping concentrations, with doping concentrations of 8×10 17 cm -3 , 1×10 15 cm -3 , thicknesses of 25nm and 35±5nm respectively. By adjusting the thickness and doping concentration, electric field control can be achieved. By adjusting the thickness and doping concentration of the charge layer, the electric field distribution can be optimized to ensure that the absorption area is kept at a low electric field and the multiplication area is kept at a high electric field, thereby improving the overall performance of the device.

[0050] The thickness of the InAlGaAs transition layer is 40nm and the doping concentration is 1×10 15 cm -3 , which can smooth the band gap between the absorption layer and the charge layer, reduce the hole accumulation effect, reduce the influence of the interface state, and improve device performance.

[0051] The material selected for the substrate is InP, which can provide mechanical support and electrical insulation.

[0052] The N-type barrier layer includes a first InAlAs layer and a second InAlAs layer.

[0053] The N-type barrier layer is composed of two layers of InAlAs with different doping concentrations. The first layer has a doping concentration range of 1×10 18 cm -3 -2×10 18 cm -3 , the second layer doping concentration range is 2×10 18 cm -3 -6×10 18 cm -3 , with the same thickness of 100nm. It can prevent electrons from penetrating directly from the multiplication layer to the bottom, ensuring that the electrons are fully multiplied in the multiplication layer.

[0054] The P-type barrier is composed of two layers of materials, InAlAs and InAlGaAs, which can prevent electrons from penetrating directly from the top to the absorption layer, ensuring that the photogenerated electrons are effectively absorbed in the absorption layer.

[0055] Figure 3 The electric field diagram after the optimization of the ten-level APD structure proposed in the embodiment of the present application is shown. By setting the charge layer doping concentration to 8×10 17 cm -3 , with a thickness of 25 nm, to achieve the regulation of the overall electric field. By setting the doping concentration of the dropping layer to 7×10 17 cm -3 , with a thickness of 17nm, to achieve the regulation of the electric field of the electron cooling layer between the high field in the multiplication region and the high field. As can be seen from the figure, the electric field in the absorption region is now 1×10 5 V / cm, which can ensure that the photogenerated electrons have enough speed to cross the transition region from the narrow bandgap absorption region to the wide bandgap charge region, and at the same time be less than the absorption region threshold electric field strength of 1.8×10 5 V / cm, which can suppress noise to a certain extent. The electric field in the multiplication region is kept at 5×10 5 V / cm, achieving a high electric field level in the multiplication zone, making the impact ionization of photogenerated electrons more concentrated. In addition, since the dropping layer is N-type doped, the impact ionization of carriers between high fields is suppressed, making the impact ionization area thinner, reducing the randomness of carrier impact ionization, and also suppressing the impact ionization of holes, thereby reducing noise.

[0056] Figure 4 The photocurrent, dark current and gain diagram of the optimized ten-level APD structure proposed in the embodiment of the present application are shown. According to theoretical calculation, the maximum gain of the device structure can reach more than 850, and when the gain is 100, the excess noise factor is 6.5. As can be seen from the figure, the device punch-through voltage is about 56V and the breakdown voltage is about 93V.

[0057] Compared with the prior art, the ten-stage multiplication avalanche photodiode proposed in the embodiment of the present application has the following beneficial effects:

[0058] First, through the series connection of multiple multiplication units, the electrons in each unit gradually accumulate gain after undergoing the processes of preheating, collision ionization, cooling and relaxation, and finally achieve very high gain, which has a higher gain effect than the single-stage multiplication structure.

[0059] Second, through the design of the electron cooling layer and the relaxation layer, the energy of electrons is effectively managed and thermal noise is reduced, so that the overall noise level is significantly reduced and the signal-to-noise ratio is improved. The design of the buffer layer reduces the sudden change of the electric field, prevents electrical breakdown, and further reduces the noise.

[0060] Third, the electric field distribution inside each multiplication unit has been carefully designed to ensure smooth transmission of electrons between layers and avoid electrical breakdown caused by sudden changes in the electric field, making the electric field distribution of the entire device more uniform and stable.

[0061] Fourth, through the effective design of the electron cooling layer and the relaxation layer, the energy of electrons can be quickly reduced, heat accumulation can be reduced, and the thermal stability of the device can be improved.

[0062] Fifth, the design of the multi-stage multiplication unit enables the avalanche photodiode to perform well in high-sensitivity and low-noise applications, and is suitable for various high-performance detectors such as night vision equipment, lidar, fiber-optic communications and other fields.

[0063] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A ten-stage multiplication avalanche photodiode based on a SAGCM structure, characterized in that: The diode is a SAGCM structure, which includes an ohmic contact layer, a P-type barrier layer, an absorption layer, a transition layer, a charge layer, a multiplication layer, an N-type barrier layer and a substrate from top to bottom; An absorption layer, used for photoelectric conversion and increasing light absorption; The transition layer is used to smooth the band gap between the absorption layer and the charge layer and reduce the hole accumulation effect; A charge layer for adjusting the electric field so that the absorption region is kept at a low electric field and the multiplication region is kept at a high electric field; The multiplication layer is used to enhance electron impact ionization and suppress hole impact ionization.

2. The ten-stage multiplication avalanche photodiode according to claim 1, characterized in that: The multiplication layer includes a plurality of multiplication units, and each multiplication unit includes a preheating layer, a buffer layer, an impact ionization layer, an electron cooling layer, and a relaxation layer.

3. The ten-stage multiplication avalanche photodiode according to claim 2, characterized in that: The impact ionization layer uses lattice-matched InAlAs and InGaAs materials, and the band gap is adjusted by controlling the Al and Ga components as the avalanche multiplication material of the multiplication zone.

4. The ten-stage multiplication avalanche photodiode according to claim 1, characterized in that: The absorption layer uses In 1-x Ga x As material, the band gap is adjusted by adjusting the composition of In and Ga.

5. The ten-stage multiplication avalanche photodiode according to claim 1, characterized in that: The charge layer is made of InAlAs material, and the electric field is controlled by adjusting the thickness and doping concentration.

6. The ten-stage multiplication avalanche photodiode according to claim 1, characterized in that: The material selected for the substrate is InP.

7. The ten-stage multiplication avalanche photodiode according to claim 1, characterized in that: The N-type barrier layer includes a first InAlAs layer and a second InAlAs layer.

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