Schottky barrier height modification on high-purity LPE GaAs following a sulphur-based etch

Nuclear radiation detectors constructed from GaAs Schottky barrier structures require control of barrier height if high resolution is to be reproducibly obtained. The authors have therefore studied the variation of device barrier height after treatment with common etching solutions. The heights of Au and Al Schottky barriers on respective samples of n- and p-type liquid-phase epitaxial GaAs were found from reverse bias I-V measurements subsequent to etching with aqua regia and 3H₂SO₄:H ₂O₂:H₂O (3:1:1). An increase in barrier height observed after the 3:1:1 etch was found to be a consequence of sulphur contamination. This result is consistent with those reported for deliberate sulphur passivation of GaAs. Low diode ideality factors, from 1.007 to 1.064, were measured for layers with carrier concentrations in the range 4*10¹⁴ cm^-3 to 2.5*10¹⁶ cm ^-3. A comparison was made between samples etched in the 3:1:1 solution at 5 degrees C and at 100 degrees C. C-V measurements gave anomalously large barrier heights for those samples etched at 5 degrees C, indicating the formation of a significant interfacial layer prior to Schottky barrier metallization, while X-ray photoelectron spectroscopy measurements confirmed the presence of a large oxide layer. No such anomalies were observed for the samples etched in 3:1:1 at 100 degrees C.