Backside SIMS Analysis and Accelerated Thermal Aging of Optimally Alloyed

Ohmic Contacts to MESFETs

 

G. Sai Saravanan1, Mahadeva Bhat K2, Sandeep Chaturvedi1, M.N. Mudholkar1, R. Muralidharan1

1Gallium Arsenide Enabling Technology Centre (GAETEC), Vignyanakancha P.O., Hyderabad-500 069,

2Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi-110 054

 

Keywords: OHMIC CONTACTS, MESFETS, BACKSIDE SIMS,

ACCELERATED THERMAL AGING

 

Abstract

Low contact resistances (Rc) of 0.05-0.07Ω-mm were achieved by rapid thermal alloying of AuGe/Ni/Au ohmic contacts to GaAs MESFETs. ‘Under-alloyed’ contacts with Rc of 0.12-0.16Ω-mm, immediately after alloying, drifted to very high values of 0.4-0.7Ω-mm at the end of fabrication process (‘final Rc’), while optimally alloyed contacts had drifted only to 0.1-0.2Ω-mm. Accelerated thermal aging for optimally alloyed samples at temperatures of 185°C to 230°C showed drifts of the order of 10 – 13% in the ‘final’ Rc values, which is one of the lowest drifts in MESFETs. Backside SIMS studies revealed the differences in the level and extent of diffusion of alloy materials between the ‘under-alloy’ and optimum alloy samples. Minimal drifts in contact resistances could be attributed to optimum germanium doping of the active layers, and formation of stable compounds in the metal-semiconductor interface and the

 

 

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