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TiAl Ohmic contact on GaN, in situ high or low doped or Si implanted, epitaxially grown on sapphire or silicon
Author(s) -
Cayrel F.,
Ménard O.,
Yvon A.,
ThierryJébali N.,
Brylinsky C.,
Collard E.,
Alquier D.
Publication year - 2012
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201127564
Subject(s) - ohmic contact , materials science , annealing (glass) , sapphire , optoelectronics , epitaxy , doping , contact resistance , silicon , gallium nitride , composite material , optics , layer (electronics) , laser , physics
In this work, the Ti/Al Ohmic contact quality on n‐type gallium nitride (GaN) films has been studied as a function of different process parameters such as surface cleaning procedure, etching, thickness of the deposited layers or annealing conditions. GaN epilayers, with uniform doping concentration from 1 × 10 16 to 5.8 × 10 18 at./cm 3 were grown on sapphire or silicon substrates using AlN and/or AlGaN buffer layers. Electrical characterizations were made using circular transfer length method (cTLM) patterns with a four‐probe equipment. Specific contact resistance (SCR) was then extracted from current–voltage ( I – V ) characteristics, for all the process conditions. Contact structures depending on experiment parameters were studied by means of (scanning) transmission electronic microscopy (STEM‐TEM). Our results reveal that process parameters such as surface treatment have a lower impact than annealing temperature or metal thickness and annealing duration. Finally, SCR values of 1 × 10 −6 Ω cm 2 can be reproducibly achieved. Moreover, good Ohmic contacts have been obtained on etched surfaces or on low‐doped layers implanted with Si. This low value demonstrates a good Ohmic contact and this large parameter process window is of high interest for future device fabrication based on GaN (planar or mesa structures).