Investigation Of Characteristics Of Quantum Well Infrared Photodetectors Under High Bias Voltage

Infrared detectors are widely used in various fields. Quantum well infrared photodetectors (QWIPs) are more mature, in material growth and device fabrication, than Mercury cadmium telluride (MCT) photodetector, which is currently the dominant photodetector. III-V semiconductors have tunable bandgap by adjusting the components in III-V compounds, which provides more flexibility in adjusting the quantum well width and the barrier height, when such kind of materials are employed in QWIPs. Consequently, working wavelength of QWIPs can be tuned to cover the three atmosphere windows with the so-called energy band engineering. Thus, QWIPs is a key candidate in infrared multi-color detection. Compared with quantum dots infrared photodetector, which is not commercialized yet, QWIPs needs to be improved in many aspects.This dissertation focuses on the optoelectronic performance under high voltage bias. Both photo current and dark current are investigated theoretically and experimentally as summarized as follows.(1) Computations are carried out to understand the energy level in multi-quantum well structure and miniband in superlattice.(2) For GaAs and AlGaAs materials, polar optical phonon scattering and inter-valley scattering was simulated. For the AlGaAs material, alloy scattering was simulated as well. The impact ionization rate was theoretically derived for quantum well structure at high bias. Further more, collision ionization rate enhancement caused by tunneling was investigated under different electric field strength.(3) The different characteristics of three different samples with different barrier materials and periods were further investigated experimentally and theoretically to found a impact ionization model in accordance with quantum well system. The relation between multiplication factor M and periods of quantum well N varying with capture probability and impact ionization coefficient was deduced.(4) Three major kinds of mechanism of dark current of QWIPs and a couple dark current investigation models were summarized. The unusual characteristics of dark current under high voltage bias were analyzed based on self consistent model. The unusual phenomena may be caused by the ground tunneling current, which is supported by the simulation under high voltage bias.(5) The contribution of defect-assistant tunneling to dark current under high voltage bias was evaluated. Defect tunneling model was found after impact ionization and ground tunneling was found to contribute little to dark current under high voltage bias. Good agreement to experimental results was obtained by setting proper defect energy band ET and the concentration NT.