Processing and characterization of epitaxial GaAs radiation detectors

TL;DR

This paper reports on the processing, characterization, and simulation of GaAs radiation detectors with epitaxial layers, demonstrating their potential for high-energy photon detection with low leakage current and fast signal transit times.

Contribution

It introduces a method for fabricating GaAs detectors with epitaxial layers and provides comprehensive experimental and simulation analysis of their electrical and charge collection properties.

Findings

Full depletion voltage: 8-15 V

Leakage current density: ~10 nA/cm²

Signal transit time: ~5 ns

Abstract

GaAs devices have relatively high atomic numbers (Z=31, 33) and thus extend the X-ray absorption edge beyond that of Si (Z=14) devices. In this study, radiation detectors were processed on GaAs substrates with 110 $\mu\textrm{m}$ - 130 $\mu\textrm{m}$ thick epitaxial absorption volume. Thick undoped and heavily doped p$^+$ epitaxial layers were grown using a custom-made horizontal Chloride Vapor Phase Epitaxy (CVPE) reactor, the growth rate of which was about 10 $\mu\textrm{m}$/h. The GaAs p$^+$/i/n$^+$ detectors were characterized by Capacitance Voltage ($CV$), Current Voltage ($IV$), Transient Current Technique (TCT) and Deep Level Transient Spectroscopy (DLTS) measurements. The full depletion voltage ($V_{\textrm{fd}}$) of the detectors with 110 $\mu\textrm{m}$ epi-layer thickness is in the range of 8 V - 15 V and the leakage current density is about 10 nA/cm$^2$. The signal transit time determined by TCT is about 5 ns when the bias voltage is well above the value that produces the peak saturation drift velocity of electrons in GaAs at a given thickness. Numerical simulations with an appropriate defect model agree with the experimental results.