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Title:Monolithic Integration of Thermally Stable Enhancement-Mode and Depletion-Mode Indium Phosphide HEMTs Utilizing Iridium-Gate and Silver-Ohmic Contact Techniques
Author(s):Zhao, Weifeng
Doctoral Committee Chair(s):Adesida, Ilesanmi
Department / Program:Electrical and Computer Engineering
Discipline:Electrical and Computer Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Materials Science
Abstract: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.
Issue Date:2006
Description:108 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.
Other Identifier(s):(MiAaPQ)AAI3243043
Date Available in IDEALS:2015-09-25
Date Deposited:2006

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