Response-enhanced type-II superlattice long-wave infrared focal plane device

Abstract

The invention provides a response enhanced type-II superlattice long-wave infrared focal plane device, the device comprises a reading circuit, a metal electrode, a type-II superlattice material layer and an indium-arsenic-antimony buffer layer which are sequentially arranged from bottom to top, a reflecting film is grown on the side wall of the type-II superlattice material layer, and after incident light enters the buffer layer and reaches the metal electrode layer, the incident light is reflected by the reflecting film. Incident light is diffracted at the metal electrode, and the other part of transverse diffracted component is reflected back to an absorption area of the device through the reflecting film, so that light loss is reduced, and the overall response efficiency of the device is improved. According to the method for integrating the metal reflecting film on the side wall of the response enhancement type II superlattice long-wave infrared focal plane device, loss caused by the fact that incident light enters a channel from the side wall of the table top is inhibited, and response enhancement is achieved.

Description

Technical Field

[0001] The invention belongs to the field of infrared detection technology, and in particular relates to a novel response-enhanced type II superlattice long-wave infrared focal plane. Background Art

[0002] Infrared radiation is an inherent property of almost all objects. Since the discovery of infrared radiation, research on it has never been interrupted. Detection of infrared bands has been widely used in military or civilian fields. At present, many material systems have been used in the preparation of infrared detectors, such as silicon, germanium, mercury cadmium telluride, type II superlattice, etc. Among them, type II superlattice materials are widely used in the preparation of long-wave infrared focal planes due to their advantages such as Auger recombination suppression, large effective carrier mass, and good uniformity.

[0003] For high-performance focal planes, dark current and quantum efficiency are very important evaluation indicators, which directly determine the detection sensitivity to a certain extent. Type II superlattice has the characteristics of flexible and adjustable energy bands. The dark current noise can be reduced to a very small level by designing a unique barrier structure, but there is still room for optimization in quantum efficiency, especially in the long-wave and very long-wave bands, when the absorption coefficient of superlattice materials is extremely reduced. Therefore, the research on the response enhancement of type II superlattice long-wave infrared focal plane devices is of great significance.

[0004] At present, many methods have been applied to the response enhancement of infrared detectors at home and abroad, such as growing anti-reflection films on the incident interface of the focal plane, integrating surface micro-nano structures, etc., to improve the response of the device by reducing the reflection or diffraction effect of the incident light to improve the propagation path of the incident light in the device. However, due to the special structure of the focal plane device, the metal electrode of the focal plane device will reflect the incident light and produce reflection loss. At the same time, the incompletely covered metal electrode will cause the incident light to diffract at the electrode interface. The focal plane device is usually a small table device, so the lateral component generated by the diffraction will pass through the side wall of the focal plane device into the channel and be absorbed by the glue filled in the channel, resulting in loss. Especially when the wavelength is extended to the long-wave direction and the diffraction effect is enhanced, a large amount of incident light will enter the channel and cause loss. And when the surface micro-nano structure is used to enhance the device response, the diffraction effect is often introduced, so the loss of the focal plane device in the channel will be enhanced, resulting in an insignificant enhancement effect or even a decrease in the device response.

[0005] In response to the above problems, considering that one of the main reasons for the low response of type-II superlattice infrared focal plane devices is that the incident light enters the channel and cannot return to the device for absorption, resulting in losses, and at the same time, there has always been a demand for high-response infrared focal plane devices. Therefore, it is urgent to develop suitable methods to reduce the channel loss of focal plane devices and thus improve the response of type-II superlattice infrared focal plane devices.

[0006] Therefore, how to solve the problem of low response of type II superlattice long-wave infrared focal plane and provide a type II superlattice long-wave infrared focal plane device with enhanced response of the focal plane device is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0007] The object of the present invention is to provide a response-enhanced type II superlattice long-wave infrared focal plane device in view of the problems in the prior art.

[0008] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions: A response-enhanced type II superlattice long-wave infrared focal plane device, characterized in that: the device includes a readout circuit, a metal electrode, a type II superlattice material layer and an indium arsenic antimony buffer layer arranged in sequence from bottom to top, a reflective film is grown on the side wall of the type II superlattice material layer, after the incident light enters the buffer layer and reaches the metal electrode layer, part of the incident light is diffracted at the metal electrode, and another part of the lateral diffraction component is reflected back to the device absorption area through the reflective film, and lateral resonance enhancement is achieved in the absorption area to reduce light loss and improve the overall response efficiency of the device.

[0009] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: the reflective film is a metal reflective film.

[0010] As a preferred technical solution of the present invention: the reflective film is a gold reflective film with a thickness of 200nm.

[0011] As a preferred technical solution of the present invention: the reflective film is a platinum reflective film or a dielectric reflective film.

[0012] Compared with the prior art, the response-enhanced type II superlattice long-wave infrared focal plane device of the present invention has the following beneficial effects: the present invention integrates a reflective film on the side wall of the table of the type II superlattice long-wave infrared focal plane device to reduce the loss of incident light entering the focal plane channel through the table, and limits the incident light to the absorption area of ​​the device, thereby improving the quantum efficiency of the focal plane device.

[0013] A response-enhanced type II superlattice long-wave infrared focal plane device of the present invention suppresses the loss of incident light entering the channel from the side wall of the table by integrating a metal reflective film on the side wall of the focal plane device table, thereby achieving response enhancement. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the existing type II superlattice long-wave infrared focal plane device model; Figure 2It is a schematic structural diagram of a response-enhanced type II superlattice long-wave infrared focal plane device of the present invention; Figure 3 This is the quantum efficiency spectrum of type II superlattice long-wave infrared focal plane device; Figure 4 Quantum efficiency, reflectivity and channel loss spectrum of focal plane devices in the long-wave band; Figure 5 To respond to the enhanced type II superlattice long-wave infrared focal plane device quantum efficiency and channel loss spectrum; In the attached drawing, air 1; buffer layer 2; type II superlattice layer 3; gold electrode 4; reflective film 5. DETAILED DESCRIPTION

[0015] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0016] Example As attached Figure 1 As shown, the common type II superlattice long-wave infrared focal plane device in the prior art is composed of the following parts: a readout circuit, a metal electrode, a type II superlattice material layer, an indium arsenic antimony buffer layer, and a gallium antimonide substrate; wherein the gallium antimonide substrate can be selected to be removed, thinned, or retained.

[0017] A response-enhanced type II superlattice long-wave infrared focal plane device of the present invention, as shown in the attached Figure 2 As shown, a response-enhanced type II superlattice long-wave infrared focal plane device is provided, which adds a metal reflective film on the side wall of the table on the basis of the existing type II superlattice long-wave infrared focal plane device to increase the optical response of the device.

[0018] Take the focal plane device with a pixel center distance of 30μm as an example: the pixel center distance of the focal plane detector is 30μm, the pixel size is 27μm, there is a 3μm channel between adjacent pixels, and a passivation layer of about 200nm is grown on the surface of the table. Based on this, a simulation model is established and the quantum efficiency spectrum of the device is obtained, as shown in the attached figure. Figure 3As shown in the figure, due to the presence of metal electrodes, the reflectivity of light at the interface between the superlattice layer and the electrode is almost 100%, while the refractive index mismatch between the buffer layer and the superlattice layer leads to the formation of a planar resonant cavity between the superlattice and the electrode interface and between the superlattice and the buffer layer interface, resulting in a violent oscillation in the quantum efficiency of the back-incident focal plane device. As the wavelength gradually increases, the quantum efficiency of the back-incident device shows a gradually decreasing trend, especially in the long-wave range of 8-12μm, the average quantum efficiency obtained by simulation is only less than 40%. This is because when the wavelength gradually increases to the long-wave band, the absorption coefficient of the superlattice absorption zone decreases rapidly, and due to the presence of the bottom metal electrode, the unabsorbed light is reflected and emitted from the incident interface, so a large part of the light loss comes from the repeated reflection at the interface between the electrode and the superlattice. The reflectivity of the focal plane device at 8-12μm is given in the attached figure (4). In the range of 8-10μm, the reflection loss of the device is very large and even higher than the quantum efficiency of the device itself; in the range of 10-12μm, both the quantum efficiency and reflection loss of the device are greatly reduced. Therefore, in addition to reflection loss, the device should have other modes of loss. In addition to being reflected back by the metal electrode at the bottom, the incident light of the back-incident focal plane device will also enter the channel. In addition to the passivation layer, the channel is filled with resin. After entering the resin, the light cannot return to the absorption zone due to the absorption of the resin. Therefore, the incident light will be lost in the channel. The specific loss is shown in the attached figure. Figure 4 Normally, not a lot of light will enter the channel and be lost, but Figure 4 It is not difficult to see that starting from 10μm, this part of the loss increases greatly.

[0019] The reason for this phenomenon is that the absorption coefficient of the superlattice decreases greatly from 10μm; but the more important reason is that the metal electrode does not completely cover the entire table, so a diffraction effect is generated, resulting in a lateral propagation mode of light. When the lateral propagation light propagates to the side wall of the table, it enters the channel and causes loss. According to the diffraction theory of light, the larger the wavelength of light, the stronger the diffraction effect generated by the slit. At the same time, the reduction of the superlattice absorption coefficient also enhances the light reaching the surface of the metal electrode, which also enhances the diffraction effect in disguise, thereby increasing this part of the loss.

[0020] The metal electrode at the bottom of the focal plane detector also acts as a reflective film. When the incident light enters the device and reaches the metal electrode, it will be reflected back and reabsorbed. However, since the metal electrode often cannot cover the entire table surface, a large amount of incident light will be diffracted at the metal electrode, generating a lateral diffraction component, which will enter the channel from the table surface and cause loss. Therefore, the side-enhanced reflective film system can suppress this part of the light loss, thereby achieving response enhancement. In short, the reflective film acted by the bottom metal electrode is for light transmitted longitudinally, while the side wall reflective film is for light propagating laterally. In addition, the side wall reflective film and the absorption area of ​​the device also form a lateral planar resonant cavity. The light reflected back to the absorption area on both sides of the absorption area will achieve the effect of lateral resonance enhancement in the absorption area, further improving the absorption rate of the device and further improving the quantum efficiency of the device. From the attached Figure 5 It is not difficult to see that the quantum efficiency spectrum of the device shows many tiny resonance peaks, corresponding to the transverse planar resonant cavity.

[0021] The loss generated by the channel comes from the fact that the light propagating laterally enters the channel and is absorbed by the resin in the channel and cannot return to the absorption area of ​​the device. Therefore, this part of the loss can be reduced by reducing the transmission of light at the sidewall interface of the table, that is, increasing the reflectivity of the interface. The simplest and most effective way to increase the reflectivity of the interface is to design a reflective film system at the interface.

[0022] Among the various reflective film systems, the metal reflective film has the highest reflection efficiency. Therefore, a metal reflective film on the sidewall is added to the simulation model of the focal plane. The material is gold and the thickness is 200nm. The performance of the focal plane device after integrating the metal reflective film is shown in the attached figure. Figure 5 As shown in the figure, the quantum efficiency of the device has been significantly improved in the 10-12μm band, from 27% to 38%, and the loss generated by the channel has also been significantly reduced, from 53% to 26%. It can be seen that the design of a reflective film on the side wall of the focal plane can effectively improve the quantum efficiency of the device, especially in the 10-12μm band.

[0023] Based on the above method, the response enhancement of type II superlattice long-wave infrared focal plane devices can be achieved, thereby improving the performance of the device.

[0024] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A response-enhanced type II superlattice long-wave infrared focal plane device, characterized in that: The device includes a readout circuit, a metal electrode, a type II superlattice material layer and an indium arsenic antimony buffer layer arranged in sequence from bottom to top. A reflective film is grown on the side wall of the type II superlattice material layer. After the incident light enters the buffer layer and reaches the metal electrode layer, part of the incident light is diffracted at the metal electrode, and another part of the lateral diffraction component is reflected back to the device absorption area through the reflective film, and lateral resonance enhancement is achieved in the absorption area to reduce light loss and improve the overall response efficiency of the device.

2. The response-enhanced type II superlattice long-wave infrared focal plane device according to claim 1, characterized in that: The reflective film is a metal reflective film.

3. The response-enhanced type II superlattice long-wave infrared focal plane device according to claim 2, characterized in that: The reflective film is a gold reflective film with a thickness of 200 nm.

4. The response-enhanced type II superlattice long-wave infrared focal plane device according to claim 1, characterized in that: The reflective film is a platinum reflective film or a dielectric reflective film.

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