Novel optoelectronic devices using intersubband transitions in gallium arsenide/aluminum gallium arsenide quantum wells and superlattices: Theory, fabrication, and measurement

The applications of novel optoelectronic devices by intersubband transition in GaAs/AlGaAs quantum wells and superlattices have attract intense interest in recent years. This study is to investigate some potential applications and properties by intersubband transition in GaAs/AlGaAs quantum wells and superlattices. The study includes modeling of the intersubband transition, material designs and characterizations, device fabrication and characterization, and the investigation of novel three terminal transistors and undoped QW IR modulators.;Modeling is specifically based on the envelope function approximation and transfer matrix method to calculate the energy levels and wavefunctions. The oscillator strength of intersubband transition then can be evaluated using the obtained wavefunctions. This model affords the capability to simulate arbitrary quantum well structures, since the potential profiles can be decomposed into sublayers with linear potential only.;Material characterizations based on the advanced techniques such as, PL spectroscopy, Fourier Transform Infrared spectroscopy, doping profiler, and double crystal X ray, are used to study the energy levels, heavy-doping induced Burstein-Moss shift and band-narrowing effect, doping profile inside the material, and quantum well layer thickness.;For most quantum effect devices, in order to contact the specific layer precisely, well-controlled fabrication techniques and procedures are very important. The diffusion length of the Au/Ge/Ni/Au ohmic contact system is on the order of 1000-4000 A on GaAs, which is not suitable for devices with thin layers. The new ohmic contact materials by Pd/Ge/Au is studied and developed for the fabrication of novel quantum well devices. This metal system has already shown very stable and wide alloying condition.;Finally, in this study, three terminal infrared transistor and all-optical IR modulator based on intersubband transition are investigated. Hot electron transistor not only shows interesting transport physics, but also potential for ultra-high speed circuit applications. Using MQW emitter, a high speed infrared phototransistor is proposed and investigated in this thesis. The other interesting HEMT-type phototransistor with 2DEG is also designed for potential high speed IR phototransistor applications.;All-optical IR modulator by interband pumping is also studied. Since the electron-hole pairs are induced by optical pumping, the magnitude of the intersubband absorption can be directly modulated by the power of the pump light.;One novel approach to populate the quantum well to required density level is also studied by electrical injection. As semiconductor lasers and LED's, the carrier density (electrons and holes) as high as 10...