The degradation of 36mm AlGaN/GaN HFETs-on-Si under DC stress conditions has been studied on a large number of nominally identical devices that were chosen randomly across a production process. A common and primary degradation phenomenon was observed in the devices. A combination of electrical and physical analysis was used to identify a possible failure mechanism related to the Ni/Au Schottky gate diode that appears to explain the degradation of the FET. Based on the analysis, a gate anneal step was added into the fabrication process of AlGaN/GaN HFETs-on-Si. Nominal devices processed using a gate anneal showed (a) a modified gate metal-semiconductor interface (b) forward diode characteristics that are unchanged upon stress and (c) improvement in overall reliability relative to control devices.

Reverse leakage current characteristics of Ni Schottky contacts to GaN grown on Si is experimentally studied using high electron mobility transistors (HEMT). The temperature in this study is between 273 K and 428 K. The reverse gate leakage current is found to be dominated by Frenkel-Poole emission, a trap-assisted process, when the reverse electric field is smaller than 1.4 MV/cm. For electric field larger than 1.6 MV/cm, the underlying mechanism is mainly Fowler-Nordheim tunneling, an electric-field-dominated process. As a result, properly engineering electric field is considered critical for reducing reverse leakage current in GaN-on-Si HEMT for high-voltage applications.

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