Research on the Semiconductor Based Optical Detector for the Short-Wavelength Visible and Ultra-Violet Region.

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We have performed this reserch project with focussing our attentions onto four fundamental key-technologies : (i) precise controling of hetero-interfaces (ZnSe-ZnSe, ZnSeZnMgSSe systems) in MBE growth, (ii) p and n type conduction control, (iii) high quality semi-insulating ZnSe layr (active layr in device), and (iv) perfect ohmic contact layr of ZnTe-Zn-Se super lattice (SLS). Concerning the MBE growth techniques, following high quality film growth conditions are established : (1) High resistive active layr (i-layr) of ZnSe : this active layr plays a role of active layr in PiN structure optical detectors and we have established the high quality i-layr with defect density of less than 10^<13>cm^<-3>. (2) SLS contact layr : almost perfect SLS ohmic contact layr (ZnTe-ZnSe superl-lattice) with the contact resistance of less than 0.1 (ohm cm^2) is realized by adjusting the N-doping conditions in MBE growth.Based on these techniques established here, we have fabricated Heter-Structure PiN optical detectors (SLS-pZnSSe-iZnSe-nZnSe on nGaAs). Tentative performance of the PiN photo-diodes are followings : (a) Quantum Efficiency=50-60% (for light wavelength region of 460-400nm), (b) dark current=0.9-0.1 nA/cm^2 at V=20 V (this value is about one order smaller in magnitudes than the cace of Si PiN diode). As described above, this research has demonstrated a very high potential of the II-VI (ZnSe) based PiN photo-diode by MBE growth for the future short wavelength visible and ultra-violet optical regions.