Structural and Electrical Characterization of Oxidated, Nitridated and Oxi-nitridated (100) GaAs Surfaces

Abstract

Oxidation by the UV & ozone process, nitridation by the nitrogen helicon-wave-excited plasma process, and the combination of these processes are applied to (100) GaAs wafers. An atomic force microscope, X-ray photoelectron spectroscopy, a transmission electron microscope, photoluminescence and electrical characteristics (current-voltage and capacitance-voltage) were used to analyze the influences of these processes on the structure and composition of the surfaces and the interfaces. Metal-insulator-semiconductor (MIS) diodes and Schottky diodes were fabricated in order to investigate the electrical influences of these processes. The oxidation slightly disorders GaAs surfaces. Nitridation of a bare surface creates about a 2nm-thick strongly disordered layer, which strongly deteriorates the electrical and photoluminescence characteristics. Nitridation of oxidated wafers (oxi-nitridation) forms firm amorphous GaON layers, which contain GaN, with very flat and sharp GaON/GaAs interfaces, where crystal disorder is hardly observed. It improves the current-voltage (I-V) and capacitance-voltage (C-V) characteristics and the photoluminescence intensity. Results of the structural and the electrical characterizations qualitatively coincide well with each other.

GaAs-MISFETs With Insulating Gate Films Formed by Direct Oxidation and by Oxinitridation of Recessed GaAs Surfaces

“…This, on the one hand implies that these are clean processes, but on the other restricts the operating conditions of the oxidation and nitridation systems so that the resist remains usable for the lift-off process. The RF power (50 W) of the treatment is much lower than that (250 W) used in our previous experiment [13].…”

“…Hara et al reported improved capacitance-voltage (C-V) characteristics of an oxidized GaAs-MIS diode by subjecting it to a helicon-waveexcited N plasma treatment [9], although Trivedi et al reported on N plasma damage of an AlGaAs-InGaAs-GaAs system [10]. Our experimental results demonstrate that N plasma nitridation after the UV and ozone oxidation forms a good quality GaAs-insulator interface with very little crystallographic disorder and improves both the electrical and the photoluminescence performance [11]- [13]. In order to check whether the beneficial effect of the N plasma nitridation is reproduced in a device fabrication process, we simultaneously fabricated GaAsMOSFETs (oxidation by UV and ozone only) and GaAs-MISFETs (N plasma after the UV and ozone oxidation) and compared their performance.…”

“…In this experiment, in order to minimize thinning of the photoresist, an RF power of 50 W was used for exciting the N plasma, which is much lower than that used in our previous experiment [13]. The authors have not yet found the optimum nitridation period under such low power conditions.…”

“…3. This suggests that the oxidized samples initially have positive charge ( cm in the oxide or cm at the interface [13]) which is neutralized by nitridation. The second bend, after nitridation, becomes sharper and shows a somewhat increased capacitance even at higher frequencies.…”

“…15 shows an energy band diagram across the MIS portion of the 4-0h sample. The deteriorated layer may be like an O doped semi-insulating semiconductor and contains positive charges as suggested by the first bend in the -curves [13]. The increase in drain current in the positive gate voltage region far beyond the flatband voltage [ Fig.…”