Surface passivation of GaAs MESFETs

The metal semiconductor field effect transistor (MESFET) represents a more realistic test for “passivation” efficacy than conventional capacitor test structures due to its prototypical fabrication process. This paper evaluates Gallium-Arsenide (GaAs) surface passivation films utilizing the MESFET as a test vehicle. For this study, gate-to-drain leakage current, gate-to-drain breakdown voltage, complex impedance versus frequency, and low-frequency noise measurements are performed on MESFETs with various passivation films. The results indicate that a hydrogen plasma used to “pre-clean” the GaAs surface in conjunction with an in situ plasma-enhanced chemical vapor deposition (PECVD) Si₃N₄ passivation film yields the best performance. In contrast, atomic-layer-epitaxial ZnSe demonstrated inferior performance (even in comparison to PECVD Si₃N₄ passivation films that did not receive a hydrogen “pre-clean”)