Mechanisms of Ohmic Contact Formation and Carrier Transport of Low Temperature Annealed Hf/Al/Ta on In0.18Al0.82N/GaN-on-Si

Abstract

The mechanisms of ohmic contact formation and carrier transport of low temperature (600°C) annealed Hf/Al/Ta on In0.18Al0.82N/GaN heterostructure grown on Si substrate have been investigated. The Hf/Al/Ta ohmic contacts have a smooth interface with In0.18Al0.82N/GaN, and the formations of HfN and Hf-Al alloy near the metal-semiconductor interface are critical to achieving good ohmic contact. Thermionic field emission (TFE) is found to be the dominant carrier transport mechanism in the Hf/Al/Ta ohmic contacts on In0.18Al0.82N/GaN and analysis of the TFE model has revealed a high carrier density of 1.72 × 1019 cm−3 and an effective barrier height of 0.48 eV. The sheet resistance of the In0.18Al0.82N/GaN substrate is shown to increase with temperature by the power-law (∝ T1.55). A series two-barrier model has been used to explain the carrier transport through the Hf/Al/Ta ohmic contacts on In0.18Al0.82N/GaN with a smooth metal-semiconductor interface. It has also been shown that the Hf/Al/Ta contacts on In0.18Al0.82N/GaN are stable at 350°C in air for more than 200 hours.