GaAs thin film epitaxy and x-ray detector development

Abstract

We report on the growth of high purity n-GaAs using Liquid Phase Epitaxy and on the fabrication of Schottky barrier diodes for use as X-ray detectors using these layers. Our epilayers are grown from an ultra-pure Ga solvent in a graphite boat in a hydrogen atmosphere. Growth is started at a temperature of approximately 800 °C; the temperature is ramped down at 2 °C/min. to room temperature. Our best epilayers show a net-residual-donor concentration of approximately 2x10'2 cm3, measured by Hall effect. Electron mobilities as high as 150,000 cm2 V1 s' at 77 K have been obtained. The residual donors have been analyzed by far infrared photothermal ionization spectroscopy and found to be sulfur and silicon. Up to approximately 200 p.m of epitaxial GaAs have been deposited using several sequential growth runs on semi-insulating and nt-doped substrates. Schottky barrier diodes have been fabricated using this epitaxial material and have been electrically characterized by current-voltage and capacitance-voltage measurements. The Schottky barriers are formed by electron beam evaporation of Pt films. The ohmic contacts are made by electron beam evaporated and alloyed Ni-Ge-Au films on the backside of the substrate. Several of our diodes exhibit dark currents of the order of 0. 3 -3 .3 nA/mm2 at reverse biases depleting approximately 50 j.tm of the epilayer. Electrical characteristics and preliminary performance results of our Schottky diodes using '°9Cd and 241Am gamma and X-ray radiation will be discussed.

Liquid phase epitaxial growth and characterization of germanium far infrared blocked impurity band detectors

“…Germanium has also been grown from Pb [Immorlica, 1980] on GaAs substrates, yielding layers with high concentrations of Ga and As. There has been recent interest in growth of ultra pure GaAs layers for x-ray and infrared detectors [Wynne, 1999] out of a Ga solution. Gallium can be obtained with very high purity (8N).…”