Conductance deep-level transient spectroscopic study of anomalous hole trap in GaAs MESFETs

The anomalous `hole' trap like peaks observed in conductance DLTS spectra of GaAs MESFETs have been previously studied and have been associated with surface states present in the ungated regions at the GaAs-passivant interface. Besides these peaks, the conductance DLTS study of thermal emission and capture by these interface traps also indicates the presence of an associated surface conducting layer. These results show that electrons from this thin conducting layer interact with the interface states giving rise to a temperature-dependent surface leakage current when the Schottky gate is reverse biased with respect to the source and/or drain. This surface current affects both the capture and the emission processes of the interface traps. From the conductance DLTS measurements on GaAs MESFETs passivated with films, we have extracted a characteristic thermal activation energy of 0.43 eV for the interface electron traps, in both of these modes. A two-dimensional interface state band model has been used to explain our experimental results reported in this work.