Far infrared and X-ray detector applications of ultrapure liquid phase epitaxial gallium arsenide.

摘要

Lightly doped n-type GaAs single crystal layers are useful for both the detection of far infrared radiation due to the very low ionization energy of the shallow donors, and of x-rays at room temperature (our interest is from 20--60 keV) due to the relatively high atomic numbers of 31 (Ga) and 33 (As) and the relatively wide bandgap of 1.42 eV at 300 K. An experimental study of the response of far infrared and x-ray detectors fabricated from high purity liquid phase epitaxial GaAs grown by the author was performed.; With respect to the far infrared radiation detector, two different photoconductive detector structures were fabricated and characterized. The expected response of the detectors to the incident radiation was observed, but the signal to noise ratio was low. This low signal to noise ratio is expected to be due to the high acceptor compensation ratio in the n-type GaAs. Research aimed at understanding and controlling compensation was left to future students because the focus of research was redirected towards room temperature x-ray detectors.; With respect to the x-ray detector, two different diode structures were fabricated and characterized. Superior performance was observed from detectors fabricated from Schottky barrier diodes. After experimenting with surface preparation and passivation techniques, it was found that incorporating a guard ring around the main contact of a Schottky barrier diode reduced the reverse bias leakage current to approximately theoretical levels, and allowed the use of special low-noise signal collection and amplification electronics to measure the detectors' response to x-rays. The response of detectors with an incorporated guard ring demonstrated the expected response to x-rays from a weak 109Cd radioactive source, but the response peak was too wide to be useful for elemental x-ray fluorescence analysis. It is expected that the added capacitance of the guard ring leads to a broad response peak that must be reduced to produce a detector for high energy resolution applications.