Abstract
The quality of ohmic contacts in pseudomorphic high electron mobility transistors (p-HEMTs) formed by sequential e-beam evaporation of Ni/Ge/Au/Ag/Au was investigated as a function of alloying cycles in the range from 390degC to 460degC for duration of 30 sec. The contact resistance (Rc) and the specific transfer resistance (ohm-mm) values of ohmic contacts so formed were measured by Transmission line method (TLM) and compared with the contacts formed without Ag interlayer. XRD technique revealed the presence of Au-Ga phase at alloying temperatures 420degC and 440degC indicative of the formation of good quality and low Rc ohmic contacts. The Ag based contacts showed improved specific transfer resistance values and smooth surface morphology at wider alloying temperatures compared to the contacts formed without using Ag as a barrier layer. This factor is beneficial in the fabrication of lower resistance ohmic contacts in HEMTs, where a deeper penetration of ohmic metal upto the 2DEG channel is desirable.
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