Ohmic Contacts for Technology for Frequency Agile Digitally Synthesized Transmitters

Researchers at The Pennsylvania State University have investigated ohmic contacts to p-InGaAs and n-InGaAs, which are needed for heterojunction bipolar transistors. They have refined an electroless deposition process for ohmic contacts to p-InGaAs in which the metals selectively deposit on the semiconductor but not on dielectric layers such as silicon nitride. This process produces contacts with a low specific contact resistance and offers the potential for self-aligned contacts. The researchers have also investigated the factors that affect the resistance of contacts to InGaAs, including premetallization surface preparation and method of deposition, and have analyzed errors involved with extracting very low specific contact resistances. This work has resulted in the recognition of reproducible trends in contact resistance with processing conditions as well as insight into how to more accurately measure the specific contact resistance of very low-resistance contacts.