PDGETIPT OHMIC CONTACTS TO P+-ALXGA1-XAS

Ohmic contacts to heavily C‐doped AlGaAs were made using PdGeTiPt that had specific contact resistances Rc, as low as 1.7×10−6 Ω cm2 when annealed at 600 °C. The less heavily doped samples annealed at temperatures between 350 and 500 °C were non‐Ohmic, and Rc decreased with increasing annealing temperature between 500 and 600 °C. For the more heavily doped samples, Rc decreased with increasing annealing temperature. Rc increased for all samples at annealing temperatures above 600 °C. Rc rose quickly by 102 when the samples were reannealed at 300 °C for 20 h, but remained unchanged with further reannealing for up to 100 h. This behavior is consistent with partial compensation generated by the rapid out‐diffusion of Ga at low annealing temperatures and the subsequent in‐diffusion of Ge into the Ga vacancies left behind. The lower Rc obtained with the 600 °C anneal can be explained by an increased As out‐diffusion and the subsequent in‐diffusion of Ge into the As vacancies at the higher annealing temperature...