Selectively Masked MBE Regrowth, Interdigitated Contacted Superlattice Optical Modulators and Three-Terminal Ballistic Electron Transistor.

Studies of quantum structure devices and surface normal superlattice devices are now being very actively pursued in optoelectronics, high speed electronics and integrated optics. The complexity of fabricating high quality interdigitated contacts and directly contacting individual quantum structures in one dimensional (1D) MBE grown structure still limits the realization of many superlattice devices and three-terminal quantum devices. The selectively masked MBE regrowth technique as well as two special doping methods, which we developed, provide possibilities to make interdigitated contacts with high quality and excellent selectivity and to contact individual quantum structures. Devices size ranging from several to hundreds of microns, can be done easily and conveniently. Surface normal superlattice optical modulators with interdigitated contacts were successfully fabricated by using these techniques. GaAs Franz-Keldysh effect doping superlattice optical modulators exhibit the highest single pass absorption change of 300%, a very wide 18 nm spectral range and a moderate modulation ratio (6:1), compared with other recent works. AlGaAs/GaAs hetero-nipi optical modulators using the bandfilling effect demonstrate a very large change of the absorption coefficient of 7850 cm^ {-1}. Both the Franz-Keldysh effect modulator and the bandfilling effect modulator require very high electric field (~10^5 V/cm) to operate. Only the high quality interdigitated contacts, made by the selectively masked MBE regrowth techniques, provide the possibility to achieve such high fields using very low operating voltages, ranging from 1 to 6 Volts. Three-terminal InGaAs/GaAs/AlGaAs quantum well base ballistic transistors have also been demonstrated by applying the selectively masked MBE regrowth technique. Contact to the 10 nm thin InGaAs quantum well base was very simple and successful. The common-base gain is approximately ~0.85, the highest reported. Several novel devices, such as superlattice tunable mirrors, high gain opto-optical bistable switches and two possible future applications, by using the selectively masked MBE regrowth technique, are briefly discussed at the end of this thesis.