Capacitance Spectroscopy of Schottky Diodes Formed on Ion-Etched GaAs
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CAPACITANCE SPECTROSCOPY OF SCHOTTKY DIODES FORMED ON ION-ETCHED GaAs S. SEN, E. D. COLE AND L. C. BURTON College of Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 ABSTRACT DLTS and low frequency capacitance measurements were made on Schottky diodes formed on Ion-beam etched (IBE) GaAs surfaces. Ion bombardment causes strong low frequency capacitance dispersion, increasing with Ion energy. This is attributed to a thin, heavily damaged region, with a trap density in excess of 1017 per cm 3 . Such dispersion disappears under weak reverse bias and at reduced temperatures. These and other measurements are consistent with a lumped R-C model having components representing the top damaged layer, the underlying space-charge region, and shunt resistance to the ohmic contact. INTRODUCTION Increasing use of Ion beam and plasma processing in semiconductor device fabrication requires a better understanding of damage caused by ion-bombardment, and of effects on device characteristics [1-4]. Toward this end electrical characteristics of Schottky diodes formed on (100) n-type GaAs surfaces that were bombarded with argon ions of up to 4keV energy were studied, with emphasis on capacitive spectroscopy. We have reported some of the properties of such ion-etched surfaces [5]: arsenic deficient, partly amorphous, reduction by a factor of 3 in the EL2 trap density. In this paper we will report on more extensive electrical measurements performed on these and similar devices. EXPERIMENTAL Ion beam bombardment, and Schottky diodes, were made on (100) GaAs obtained from two vendors. These were n-type wafers, Si-doped to 5 x 6 101 cm- 3 . Following standard cleaning procedures [5], Ar+ Ion bombardment was carried out at energies from 0.5 to 4keV, in a Perkin-Elmer 5300 XPS system. Ohmic contacts were made with 88:12 Au:Ge, with a Ni cap prior to ion bombardment; annealed at 450°C for 2 min. in forming gas, at atmospheric pressure. Schottky barriers were made using both Au and Al dots, of 1.5mm diameter. Capacitance measurements were made on an HP 4192A Impedance Analyzer. RESULTS AND DISCUSSION DLTS measurements were performed on Schottky diodes fabricated on virgin and IBE material. A striking difference between virgin material obtained from two vendors is seen in Figure 1. Trap parameters are indicated In the table. Material from one vendor only contains EL2 defects; the other contains roughly twice the EL2 density, plus additional defects (see table.) It is not known precisely what effect, if any, these additional traps have on device quality. Schottky diodes made on the two materials were very similar, with regard to diode ideality factor, reverse saturation current and breakdown voltage.
Mat.Res. Soc. Symp. Proc. Vol.100. c1988Materials Research Society
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