The Effects of Low Energy Ion-Beam Milling on the Physical and Electrical Properties of N-GaAs.
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W.F. Seng* and P.A. Barnes, Department of Physics, Auburn University, AL 36849-5311; M.L. Lovejoy, Sandia National Laboratories, Albuquerque, NM 87185; L.P. Fu, GD. Gilliland, Department of Physics, Emory University, Atlanta, GA 30322; D. Ila, Alabama A&M University, Center for Irradiation of Materials, Normal, AL 35762 *Present address: Department of Physics, Michigan Technological University, Houghton, M1
ABSTRACT Low energy neutral Ar ion-beam etching of n-GaAs was investigated as a possible
"cleaning" procedure prior to contact metallization. The ion-beam source energy was varied between 35 eV and 1200 eV at a fixed current density of 1 mA/cm2 . The effects of ion-milling on lightly doped n-GaAs were analyzed electrically by measuring current-voltage (IV) and capacitance-voltage (CV) characteristics of Schottky barriers formed after the ion-milling. The metal semiconductor barriers were prepared immediately following ion-milling without breaking vacuum. Photoluminescence and Rutherford Backscattering (RBS) were used to determine if any physical modification of the surface and near surface region of the ion-milled substrates had occurred. INTRODUCTION. Ion beam etching has been used historically as a technique for mesa isolation of GaAs based devices. [1-3]. The ion-beams used have energies in the keV to several keV range in order to remove material at a reasonable rate. In this paper we report on a study to determine if ionmilling can be used as a "cleaning" step prior to device metallization. The work to be described investigated the effects of neutral Ar ion milling upon the Schottky barrier height of n-GaAs. We are attempting to determine the possible use of in situ Ar ion cleaning to prepare the surface for reproducible contacts on compound semiconductors such as GaAs, InP, GaN, InN, AIN and their
single crystal alloys. Preliminary experiments were performed on semi-insulating GaAs and ntype GaAs with doping (Nd - Na) = 7 x 1017/cm 3. The Ar ion cleaned samples were examined using optical and electron (SEM) microscopy. photoluminescence and Rutherford Backscattering. Photolithographically patterned samples were prepared for electrical evaluation using IV and CV measurements. EXPERUVIENT. The procedure employed in this series of experiments was to clean n-GaAs by standard organic solvent cleaning followed by a de-oxidizing rinse in HCl:H 2 0 (1:1), ion-mill the samples at energies (voltages) ranging from -35 to 1200 eV with constant geometry and fluence, and then pattern and deposit Ni/Al Schottky barrier contacts. The samples were prepared, examined optically and with the SEM and characterized using Current-Voltage (IV) and CapacitanceVoltage (CV) measurements at Auburn University. Photoluminescence (PL) studies of ion-milled samples were performed at Emory University; and RBS studies at Alabama A&M University. Samples were prepared in a CHA SE-600 electron beam deposition system at a
nominal background pressure of-5 x 10-7 Torr. The system is pumped using a 6 inch diffusion pump loaded with DC704 pumpi
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