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Title:Advanced process development for contacts to algan/gan high electron mobility transistors (HEMTS)
Author(s):Ofuonye, Benedict C.
Director of Research:Adesida, Ilesanmi
Doctoral Committee Chair(s):Adesida, Ilesanmi
Doctoral Committee Member(s):Schutt-Ainé, José E.; Hsieh, Kuang-Chien; Ravaioli, Umberto
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):AlGaN/GAN
Implantation
Contacts
Schottky
Ohmic
Thermal Annealing
Stability
Self-aligned
Gallium Nitride (GaN)
Activation
Selective-Area
Metallization
Abstract:High work function metals--Ni, Pt, Ir, and Au--were comparatively studied as Schottky metallizations to GaN and AlGaN/GaN heterostructures. Ni/Au, Ni/Pt/Au, Ir/Au, Ir/Pt/Au and Pt/Au Schottky diodes were fabricated on GaN and AlGaN/GaN substrates. Schottky barrier heights ranging from 0.8 to 0.9 eV were obtained as-deposited on GaN with ideality factors of about 1.05. The quality of the Schottky diodes was evaluated and their thermal stability also was studied. The interposition of Pt in Ni/Au and Ir/Au systems was found to improve the characteristics of the Schottky diodes. Ir/Pt/Au diodes were found to be more thermally stable than Ni/Pt/Au diodes. Ni/Au Schottky contacts exhibited good leakage response under thermal annealing for long periods. Microstructural studies were carried out on Ni/Pt/Au and Ni/Au Schottky contacts to elucidate the role of the intermediate layer, Pt, in the degradation of the Ni/Pt/Au metallization under long-term thermal anneal. A selective-area silicon ion implantation process for ohmic contact resistance improvement to AlGaN/GaN high electron mobility transistors (HEMTs) was developed. Non-alloyed ohmic contacts with very low contact resistances of 0.2 - 0.24 -mm were achieved with TLM pads fabricated using the Mo/Al/Mo/Au metallization. Simulations were carried out with SRIM to qualify the implantation process. Surface chemistry analysis was undertaken on the implanted AlGaN/GaN and GaN samples to determine the impact of implantation on the surface morphology of the AlGaN layer. The developed ion-implantation process was used to propose fabrication schemes for novel high speed self-aligned and non-self-aligned AlGaN/GaN high electron mobility trasistors (HEMTs) employing Ir/Pt/Au or Ni/Au gate and non-alloyed ohmic contact metallizations.
Issue Date:2010-01-06
URI:http://hdl.handle.net/2142/14559
Rights Information:copyright 2009 Benedict Chukwuka Ofuonye
Date Available in IDEALS:2010-01-06
Date Deposited:December 2


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