Monolithic Integration of Thermally Stable Enhancement-Mode and Depletion-Mode Indium Phosphide HEMTs Utilizing Iridium-Gate and Silver-Ohmic Contact Techniques

Excellent ohmic contacts based on Ge/Ag/Ni metallization have been developed for InAlAs/InGaAs/InP high electron mobility transistors (HEMTs) in a temperature range between 385 and 500°C for the first time. A minimum contact resistance of 0.06 O-mm was obtained at an annealing temperature of 425°C for 60 s in a rapid thermal annealing system. Thermal storage tests showed that the Ag-based ohmic contacts had far superior thermal stability than the conventional AuGe/Ni ohmic contacts for InAlAs/InGaAs/InP HEMTs. Auger electron spectroscopy and transmission electron microscopy study for both Ag-based and Au-based ohmic contacts confirmed that metal protrusions created by diffusion of contact metals linked the two-dimensional electron gas layer with the metal contacts to produce excellent ohmic contacts. The formation of liquid AuGe eutectic phase in the AuGe/Ni/Au metallization at relatively low temperature is believed to cause overannealing. The eutectic temperature of Ag-Ge is about 300°C higher than that of the Au-Ge system, leading to a much wider processing window and much better thermal stability for the Ge/Ag/Ni ohmic contacts. After a detailed electrical and microanalysis study of Shottky diodes based on Ir/Ti/Pt/Au metallization, a fabrication process for the realization of thermally stable InAlAs/InGaAs/InP enhancement-mode HEMTs based on annealed Ir-gate and Ge/Ag/Ni-ohmic contacts were developed subsequently. The enhancement-mode InAlAs/InGaAs/InP HEMTs with a gate-length of 0.1 mum demonstrated excellent DC and RF characteristics including: threshold voltage of 198 mV, Gm, max of 945 mS/mm, IDSS of 0.25 mA/mm, and fT of 205 GHz. Thermal stability study of these devices showed that no degradation of the extrinsic transconductance and drain current was observed at storage temperature of 215°C for a storing period of 96 h. At the same time, stable operation of the Ir/Ti/Pt/Au-gate contact was also obtained. Finally, by optimizing the HEMT layer structure and the doping concentration, monolithic integration of depletion-mode and enhancement-mode InAlAs/InGaAs/InP HEMTs were realized through the newly developed fabrication process based on Ge/Ag/Ni-ohmic and Ir-gate contact technologies, which are highly applicable to high speed integrated circuits.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical and Computer Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Zhao, Weifeng

Contributors dc:contributor

• Adesida, Ilesanmi

• Engineering, Materials Science

Language dc:language

eng

Identifier

(MiAaPQ)AAI3243043

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/80990