Processing and characterization of epitaxial GaAs radiation detectors
X-ray detectors made on thick epitaxial GaAs were successfully processed.
CVPE technique was used to grow high purity epi-GaAs with over layer thickness.
Leakage current density of about 10 nA/cm2 indicates high purity of the epi-layer.
DLTS shows a significant concentration of deep level electron traps in the epi-layer.
TCAD simulations with a deep level trap in the epi-layer reproduce the measurements.
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 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 . 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 (Vfd) of the detectors with epi-layer thickness is in the range of 8–15 V and the leakage current density is about 10 nA/cm2. 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.