Development the semiconductor photorefractive devices employing asymmetric quantum well structures

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The purpose of this research project is to improve the properties of semiconductor photorefractive devices by employing asymmetric coupled quantum well structures.(1) Improvement of spectral bandwidth : Femto-second pulse shaping is one of the interesting applications of photorefractive devices. However, the spectral bandwidth of conventional AlGaAs multiple quantum well devices are limited within 4 nm in wavelengths. This bandwidth is too narrow to handle femto-second pulses. In order to broaden the spectral region, we have employed an asymmetric coupled quantum well structure, where two different quantum wells are coupled through thin coupling layers. We can tailor the electro-absorption spectrum of excitonic resonance by controlling the thickness and depth of wells and coupling layers. We have designed and fabricated several asymmetric quantum well structures and have measured the photorefractive properties. Finally, the spectral bandwidth of response is broadened up to 12 nm in wav … More elength. Moreover, the asymmetric quantum well structure improved the sensitivity substantially.(2) Improvement of spatial resolution : In p-i-n diode structures, the external field is applied longitudinally through the multiple quantum well layers. In this geometry, photo-induced charges are trapped in cladding layers. Therefore, the energy step between the multiple quantum well layers and the cladding layers plays an important roll in the performance of this device. We have fabricated several device structures that have different potential energy of cladding layers by changing the fractions of Al and Ga. We found that the reduction of energy step improves the spatial resolution of device. It is found that the temporal behavior is also influenced by the potential of cladding layer.(3) New material GaN : We demonstrated, at the first time, the photorefractive effect in a semi-insulating GaN thin layer at the wavelength of 363.6 nm, which is the shortest wavelength at which the photorefractive effect has ever been demonstrated in semiconductors. Less