AVS 47th International Symposium
    Semiconductors Friday Sessions
       Session SC+EL-FrM

Paper SC+EL-FrM3
Effects of Etch Processing on Contacts to n-GaN

Friday, October 6, 2000, 9:00 am, Room 306

Session: III-Nitride Processing and Devices
Presenter: R. Singh, Boston University
Authors: R. Singh, Boston University
C.R. Eddy, Jr., Boston University
H.M. Ng, Lucent Technologies
T.D. Moustakas, Boston University
Correspondent: Click to Email
We report studies on the effects of high density plasma etching on the properties of ohmic contacts to n-GaN. Samples deposited by plasma-assisted MBE on a-plane sapphire and doped with Si are used in this study. Inductively coupled high density chlorine plasmas are applied to etch the surfaces of GaN and subsequent contacts (Ti/Al) to these etched surfaces are evaluated. We identify degradation of contact ohmicity even for very low rf bias powers (ion energies) as a function of the doping level in the GaN film. For films of high doping levels (3x10@super 18@ cm@super -3@), as might be encountered in a laser or LED structure, the degree of contact degradation, compared to the control sample, is a modest factor of 2 (4x10@super -4@ @ohm@cm@super -2@ to 1x10@super -3@ @ohm@cm@super -2@). However, for lower doping level films (10@super 17@ cm@super -3@), as might be encountered in electronic devices, the specific contact resistance is higher by almost two orders of magnitude for the same treatment (5x10@super -3@ @ohm@cm@super -2@ to 2x10@super -1@ @ohm@cm@super -2@). These as-deposited contacts are then rapid thermal annealed (700°C) in a nitrogen atmosphere, where specific contact resistance is monitored as a function of annealing time. Although there is improvement in contact resistivity, the effect of plasma exposure is still evident even at a cumulative rapid thermal annealing time of 280 seconds. We show that even modest ion energies in highly reactive chemistries can lead to contact degradation and that care must be taken in applying such processes if highly efficient power devices are to be routinely realized. In an effort to identify the cause of the degradation, we will also report SEM, AFM and surface sensitive photoluminescence measurements of the as etched surfaces. We will also discuss in-situ and ex-situ efforts to eliminate such degradation.