Characteristics of nuclear radiation detectors based on semi-insulating gallium arsenide

Abstract

The characteristics of detectors based on bulk semi-insulating GaAs (SI-GaAs) have been studied by α particle detection and spectrometry. A distinctive feature of these detectors is the dependence of the width of the space charge region W on reverse bias voltage U. The rate of increase in W(U) is ∼1 µm/V, which permits formation of a sensitive region a few millimeters thick. The main obstacle to applying kilovolt-range bias voltages U is the reverse current noise. The characteristics of diode structures in which a rectifying barrier to SI-GaAs was formed by metal deposition (Schottky diodes) and by growing heterostructures with heavily doped AlGaAs or GaAsSb epitaxial layers were compared. Nonequilibrium carrier transport in epitaxial structures capable of sustaining bias voltages above 1 kV was investigated in both weak (below 1 kV/cm) and strong (10–30 kV/cm) electric fields. In both cases, the carrier lifetimes were found to be about a few nanoseconds. Such low values are due to the high concentration of trapping centers (EL2-type native defects), which limits the carrier transport. An analysis of the spectral line shape revealed that the lifetime is almost constant throughout the detector volume. The charge introduced by a particle was found to be enhanced in fields of ∼30 kV/cm. This effect can be qualitatively explained by focusing the electric field lines at the vertex of the α-particle track, which leads to an increase in the local field strength to ∼10−5 V/cm and impact ionization by nonequilibrium electrons.