Processing and characterization of epitaxial GaAs radiation detectors

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 $\mu \text{m}$

• 130 $\mu \text{m}$ 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 $\mu \text{m}$/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 ($V_{\text{fd}}$) of the detectors with 110 $\mu \text{m}$ 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.