Bio-photosensors based on monolithic integration of light sensitive proteins with semiconductor devices and integrated circuits

This Ph.D. work is aimed to study the integration of a suitably engineered protein, bacteriorhodopsin (BR), with semiconductor optoelectronic devices and circuits. A detailed study was carried out on the coupling mechanism at the protein-semiconductor interface. It was found that electrophoretic deposition of dried protein membranes is best suited for reliable integration with semiconductor devices. In the course of this study, the photoelectric response time was directly measured by a femtosecond electro-optic sampling technique. The measured transient response time of 4.5 picosecond, gives valuable information in the photocycle and kinetic processes associated with the photoisomerization.; A highly sensitive bio-photosensor was designed and demonstrated, for the first time, based on the monolithic integration of bacteriorhodopsin and GaAs/AlGaAs modulation doped field effect transistors (MODFET). In this device, the small photovoltage generated by the protein is applied to the gate of the transistor embedded underneath, and therefore amplified and transformed into a large current signal. A light responsivity of 3.8 A/W was measured. Following this, double stage high gain MODFET-based transimpedance amplifier circuits were designed and monolithically integrated with the BR/FET bio-photosensors. The integrated bio-photoreceiver circuit exhibits a high responsivity of 175 V/W. The photoresponse was measured to be linear within several orders of magnitudes of the peak intensity of the light pulses. Unlike most semiconductor photodetectors, this bio-photosensor exhibits high sensitivity to change in incident light intensities, which is the essence of motion and edge detection. Polarization sensitive detection with the bio-photosensors was also demonstrated. This was achieved by photochemically modifying the molecular arrangement of the protein molecules inside the protein membrane.; In addition, a dual focus electro-optic micro-Fresnel lens was developed for an artificial vision system. The lens device was built with GaAs/AlGaAs multiple quantum well absorbers that are patterned into the Fresnel zones. A contrast ratio of 7:1 was achieved between the focusing and defocusing states of the micro-lens.