PhD Defense: "Development of Ultra-Low Resistance Ohmic Contacts for InGaAs/InP HBTs"

Ashish Baraskar

May 13th (Friday), 1:00pm
Engineering Science Building (ESB), Rm 1001

Very low resistance metal-semiconductor contacts are an enabling technology for high-performance transistors in the Terahertz domain: base and emitter contact resistivities in heterojunction bipolar transistors (HBTs) must decrease in proportion to the inverse square of the transistor cutoff frequency. Degenerately high active carrier concentrations and efficient surface preparation techniques are required to obtain ultra-low resistance contacts. Additionally, thermal stability of the contacts is crucial to attain high reliability for THz transistors that operate at high current densities for extended periods of time. In this work, the approach to obtain degenerate active carrier concentrations in n-In(0.53)Ga(0.47)As, n-InAs and p-In(0.53)Ga(0.47)As using molecular beam epitaxy (MBE) technique is discussed. Contacts with ultra-low resistivities were fabricated with various refractory metals (W, Mo, Ir) using different surface preparation techniques. Transmission line model structures were designed to accurately extract the contact resistivities. A theoretical model has been developed to estimate minimum possible contact resistivities for these metal-semiconductor contacts, and it has been applied to validate the experimental data.

Hosted by: Professor Mark Rodwell