Heterostructure devices using self-aligned p-type diffused ohmic contacts

Describes the use of a p-type refractory ohmic contact in ohmic self-aligned devices. The contacts are based on self-aligned diffusion of zinc-doped tungsten film. The diffusion is nearly isotropic in the vicinity of silicon nitride sidewalls, allowing self-alignment of ohmic contacts with emitters and gates. Low-resistance contacts (<10/sup -6/ Omega .cm/sup 2/) are formed both to GaAs and GaAlAs, and the lifetime of the diffused region is superior to that obtained from implantation. Heterostructure bipolar transistors (HBTs) showing high current gains (>or=50 at 2*10/sup 3/ A.cm/sup -2/ and >or=200 at 1*10/sup 5/ A.cm/sup -2/ with micrometer-sized emitter widths) and p-channel GaAs gate heterostructure field-effect transistors (HFETs) showing high transconductances (78 mS/mm at 2.2- mu m gate length) have been fabricated using this contact.<>