A method of manufacturing a semiconductor device having an improved ohmic
contact system to epitaxially grown, low bandgap compound semiconductors.
In an exemplary embodiment, the improved ohmic contact system comprises a
thin reactive layer of nickel deposited on a portion of an epitaxially
grown N+ doped InGaAs emitter cap layer. The improved ohmic contact system
further comprises a thick refractory layer of titanium or other suitable
material deposited on the thin reactive layer. Both the reactive layer and
the refractory layer are substantially free of gold and other low
resistivity, high conductivity metal overlayers. The improved ohmic
contact system and method for forming the same minimize contact
resistance, improve reliability and the long-term stability of the
electrical characteristics of the device, minimize raw material costs, and
decrease manufacturing costs on high performance semiconductor devices,
such as heterojunction bipolar transistors, laser diodes, light emitting
diodes (LEDs), Schottky diodes, field effect transistors (FETs),
metal-semiconductor field effect transistors (MESFETs),
metal-oxide-semiconductor field effect transistors (MOSFETs), high
electron mobility transistors (HEMTs), and other compound semiconductor
and optoelectronic devices.
