On-chip High-polarization Multispectral Quantum Well Infrared Photodetector

Multispectral and/or polarization imaging are the key focus of the next generation of infrared cameras.Compared to monochrome or panchromatic imaging,narrow and multispectral imaging can provide more abundant object information,making it possible to determine the absolute temperature of the object,and reducing the sensitivity of the camera to atmospheric conditions.The combination of several adjacent spectral channels facilitates the detection of buried objects in complex environment.On the other hand,artificial objects(such as metal and glass)normally have different polarization characteristics to that of natural objects.Acquiring polarization information therefore has the potential to identify certain objects,and is considered to be an important means to improve identification efficiency and reduce false alarms.Traditional multispectral and polarization technologies are based on the incorporation of broad-band focal plane array,spectrometers or dispersive lens and polarizers,which often requires high-cost mechanical scanning instrument and extra space,resulting in large volume and high cost imaging instruments.Therefore,people want to integrate these functions directly on the pixels to achieve miniaturization,low cost,low power consumption and high stability imaging instruments.In order to achieve high-performance multi-function infrared detectors,great efforts have been made to integrate camera pixels with spectral or polarization detection capabilities.The key is to make the pixel have multi-spectral or narrow-band response and polarization dependence.In most cases,micro filters or micro polarizers are used for on-chip integration of related detection functions.However,there are problems such as material matching and assembly difficulty between these optical units and the focal plane,which limits their further application.Here,we design and fabricate QWIPs with metallic cavity(MC-QWIP)that not only realize very narrow wavelength selective detection but also possesses very high polarization extinction ratio.At the same time,the device process technology is fully compatible with the existing focal plane process,so it can achieve true multifunctional on-chip integration.The main work of this paper is as follows:1.The quantum well absorption model is studied and the simulation model of MC-QWIP is established.Several different material structures were designed using Ga As/Al_xGa_1-xAs.The detection wavelengths locate at the absorption bands of CH₄(?8?m)and SF₆(?10.6?m),respectively.2.Based on the rectangular metal cavity,a formula for predicting the resonance wavelength of the cavity mode is given.The mode number of the cavity was analyzed using standing wave conditions,which explains why the mode number of MC-QWIP is 1/2 in the Z direction.According to the simulation results of quantum efficiency,the factors need to be concerned when optimizing the optical coupling structure are summarized.3.According to the theoretical analysis and simulation results,MC-QWIP devices are designed and fabricated.Test results show that,compared with the standard 45°QWIP,MC-QWIP can increase the blackbody response by about 2 times and the peak response by at least 7 times.The response spectra of MC-QWIPs are very narrow,and a quality factor of up to 60(peak wavelength?5.71?m)has been observed.The peak response wavelength can be adjusted according to the size of the mesa,so the combination of different sizes can achieve narrow-band and multi-spectral detection.MC-QWIP also has strong polarization sensitivity.At 9.13?m,MC-QWIP achieves a polarization extinction ratio of 146.The theoretical and experimental results of MC-QWIP are compared and analyzed.The results show that the proposed metal cavity resonance theory is in good agreement with the experimental results.The effect of incident angle on the response spectrum of the device was also studied.The results show that MC-QWIP has stronger angular stability than Fabry-Perot filters and plasma filters.4.A filter free MC-QWIP is proposed for SF₆ gas detection.According to the simulation results,the absorption quantum efficiency of MC-QWIP can be high(?74%)with a very low doping concentration in the quantum well(?1×10¹⁷ cm^-3).The simulated dark current of the device shows that the dark current of MC-QWIP can be reduced by at least an order of magnitude compared to R-QWIP(doping concentration?1×10¹⁸ cm^-3),while the quantum efficiency is almost the same.It is expected that this MC-QWIP design will be an effective way to improve the detection performance of the QWIP device.