Theoretical design and material growth of Type-II Antimonide-based superlattices for multi-spectral infrared detection and imaging.

摘要

Infrared detectors find applications in many aspects of life, from night vision, target tracking for homeland security and defense, non-destructive failure detection in industry, chemical sensing in medicine, and free-space communication. Currently, the dominant technologies of photodetectors based upon HgCdTe and InSb are experiencing many limitations. Under this circumstance, the Type-II InAs/GaSb/AlSb superlattices which have been intensively studied recently appear to be an excellent candidate to give breakthroughs in the infrared technology. The Type-II SLs with theirs advantages such as great flexibility in bandgap engineering, high carrier effective mass, Auger recombination suppression and high uniformity have shown excellent device performance from MWIR to VLWIR. In the era of the third generation for infrared cameras, Type-II SLs are entering the new phase of development with high performance and multi-spectral detection.;The goal of this work is to investigate quantum properties of the superlattice system, design appropriate device architectures and experimentally fabricate infrared detectors which can push further the limit of this material system and outperform existing competing technologies. The binary-binary InAs/GaSb superlattice has gone through much transformation over the years. Incorporating compounds lattice matched to the 6.1A family has invited more possibilities to band engineer the Type-II SLs. For the first time, by employing all three members of this material system, we have designed a new superlattice structure and demonstrated shortwavelength infrared (SWIR) photodiodes based on Type-II InAs/GaSb/AlSb with high electrical and optical performance. The photodiodes exhibited a quantum efficiency of 60% with very low dark current, can be operated at room temperature. In addition to the range of MWIR to VLWIR, a new channel of detection has been added to the GaSb based type-II SL material system.;The new realization of SWIR photodiodes has led to the possibility of incorporating this channel to the multi-spectral detection. By combining with the MWIR channel, dual-band SWIR-MWIR photodiodes and focal plane arrays have been demonstrated, giving the capability of delivering both active and passive imaging in one single camera. Dual-band SWIR-MWIR photodiodes with quantum efficiency more than 50% for each channel has been achieved. Just like visible imaging, besides the available dual-band detection, the prospect of incorporating the third infrared waveband detection is very promising for a wide range of applications. However, the challenges for making such devices are so many that little success has been achieved. In the work, we also propose a new approach in device design to realize bias-selectable three-color shortwave-midwave-longwave infrared photodetector based on InAs/GaSb/AlSb type-II superlattice. The effect of conduction band off-set and different doping levels between two absorption layers are employed to control the turn-on voltage for individual channels. For the first time, we demonstrate experimentally Type-II superlattice based three-color photodiodes without using additional terminal contacts. As the applied bias voltage varies, the photodiodes exhibit sequentially the behavior of three different colors, corresponding to the bandgap of three absorbers. Well defined cut-offs and high quantum efficiency in each channel are achieved. While retaining the simplicity in device fabrication, this demonstration opens the new prospect for three-color infrared imaging.;Finally, for further improvement, we are looking toward new type-II material called InAs/InAsSb superlattices. Theoretical design and growth techniques have been developed to investigate the properties of this material. We successfully demonstrated the design and growth of MWIR to VLWIR photodiodes based on Type-II InAs/InAsSb with high performance. Given the fact that these two Type-II material systems share the same GaSb substrate, a new incorporation could further fully exploit their advantages in the near future.;Theoretical design, growth and optimization of device performance in each work are discussed.