| Due to its high quantum efficiency,high operating temperature range,continuously adjustable bandgap and high electron mobility,HgCdTehas become the most competitive infrared detection material in the field of high speed,high resolution and hyperspectral detection.With the second generation of HgCdTeIRFPA technology gradually into the industrial production,the third generation of HgCdTeIRFPA technology research is also launched.However,the application of HgCdTefocal plane detector based on traditional PN junction is significantly affected by its dark current characteristics,and is unable to achieve the breakthrough in the field of high temperature detection and weak signal detection.Therefore,the barrier-blocking HgCdTeoptoelectronic devices based on band engineering are studied in this paper.The physical characteristics and structure optimization design of HgCd Te-nBn devices are explored from two aspects of process and device performance.Furthermore,we coupled the barrier-blocking structure into HgCdTeavalanche detector,and further introduced the two-color detection function into the device.We designed the structure of pBp-APD,Auger suppressed nBvn,dual-band nBn and dual-band pBp-APD structures,which are designed for the new generation HgCdTeinfrared focal plane devices with high operating temperature,high gain,low dark current and dual-band detection ability.The research and development provide theoretical basis and device design guidance.The specific research contents and main research results are as follows:1.Research on LWIR HgCdTenBn photodetectors.For HgCdTedevices,nBn detector can avoid the difficulty of preparing P-type materials,and its suppression effect on SRH current and surface leakage is also helpful for LWIR HgCdTedevices with low leakage current and high performance.Based on the experimental results,the simulation model of LWIR HgCdTenBn photodetector is established by using Sentaurus-TCAD simulation software.The valence band-offset and minority carrier barrier can be significantly reduced by adding a grading layer on both sides of the barrier layer,thus could significantly improve the transport of photogenerated carriers.The detectivity could be increased by more than two orders of magnitude at 180 K.The physical characteristics such as depletion region,band structure and optical response are extracted and analyzed,and the optimal operating voltage of LWIR HgCd Te-nBn device has been found.The simulation also considers the influence of the Cd composition and doping diffusion brought by the annealing process on the device performance.The results show that the annealing will lead to a large deviation between the actual structure and the design value,which will significantly increase the dark current.In addition,we consider the device performance from both the dark current and response,and the device structure and physical parameters(including thickness,doping concentration and cadmium component)are optimized.The model and simulation results in this paper can provide important theoretical support for the further study of LWIR HgCd Te-nBn devices.2.Design and study of barrier-blocking pBp-APD structure of HgCd Te.APD has been widely used in weak signal detection because of its signal amplification effect.However,the practical application of HgCdTeAPD is seriously limited by its high dark current due to its internal gain effect,especially at high operating temperature.In this study,a new barrier-blocking LWIR HgCdTepBp-APD structure was proposed and its performance was compared with that of conventional mesa HgCd Te-APD.The results show that the dark current can be reduced by more than one order of magnitude at 260 K compared with the conventional APD.Further studies show that the key to the dark current suppression effect is to reduce the avalanche dark current.By further extracting and studying the intrinsic physical properties of pBp-APD devices,we reveal that the physical essence of the effect of avalanche dark current suppression is the depletion of carriers in the absorption region.The feasibility of improving the structure is also further confirmed by analyzing the energy band and electric field distribution.In addition,the reduction of gain normalized dark current(GNDC)by pBp-APD at high temperature does not need to sacrifice gain characteristics.Then we further calculated and analyzed the physical characteristics of the pBp-APD device under different structural parameters,and made it clear that the key point of the design of the pBp-APD structure is to control its electric field distribution characteristics.The innovative structure design of LWIR pBp-APD will greatly contribute to the development of infrared HgCd Te-APD to high operating temperature.3.Study on Auger-suppressed nBvn devices.In order to increase the operating temperature HgCdTedevices,nBvn structure is proposed to deplete the carrier concentration in the absorption region to reduce the leakage current.In this study,the mechanism of Auger suppression in nBvn structure is analyzed,and it is revealed that the physical mechanism of the auger suppression is the depletion of holes in the absorption region.By comparing the dark current characteristics of nBvn and nBn,it is further confirmed that HgCdTenBvn structure can suppress dark current at high temperature.In addition,the traditional nBvn structure design usually introduces additional heterojunction,which significantly improves the process requirements.In this study,the dark current characteristics of two different structure nBvn structures are analyzed and compared.The results show that the introduction of additional heterojunction does not significantly improve the leakage current characteristics of devices,while the introduction of homojunction design can reduce the difficulty of fabrication.This work can provide theoretical and technological guidance for the fabrication of high temperature LWIR HgCd Te-nBvn devices.4.Research on dual-band HgCdTenBn device.Dual-band detection is an important part of the third generation HgCdTeinfrared focal plane,and the special structure design of nBn makes it could realize dual-band detection.In this study,the dual-band detection performance of HgCd Te-nBn detector is studied.The results show that the device structure has excellent dual-band detection function,which can maintain high response rate and suppress medium wave spectral response when working at LWIR detection mode.The MWIR detection mode could work at near zero bias,which can significantly improve the image output rate.Compared with the general nBn structure,the dual-band detection mode can improve the MWIR quantum efficiency without introducing more additional bulk dark current.5.Dual-band detection of HgCdTepBp APD-device.Both military and civil fields have put forward higher requirements for HgCdTeinfrared APD and dual-band detection.However,there is no report that coupling these two detection functions.In this study,we designed a HgCdTepBp-APD device structure with duan-band detection ability.The results show that the structure has excellent duan-band detection function.The results of the band structure in the MWIR mode show that the further improvement of the reverse bias by the medium wave detection will not destroy the dark current suppression effect of the barrier-blocking design.Further analysis of the electrostatic potential distribution and dark current characteristics shows that the introduction of dual-band detection structure will not lead to large forward diffusion current.The proposed dual-band detection pBp-APD structure is expected to further expand the development of high operating temperature and low dark current APD devices to the field of dual-band detection. |
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