Heterostructure Devices Using Self-Aligned p-Type Diffused Ohmic Contacts

We describe 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. Lowresistance contacts (< 10-6 Ω. cm2) are formed both to GaAs and GaAIAs, and the lifetime of the diffused region is superior to that obtained from implantation. Heterostructure bipolar transistors (HBT's) showing high current gains (≥50 at 2 x 103 A.cm-2 and ≥200 at 1 x 105 A.cm-2 with micrometer-sized emitter widths) and p-channel GaAs gate heterostructure field-effect transistors (HFET's) showing high transconductances (78 mS/mm at 2.2-μm gate length) have been fabricated using this contact.