Formation of thermally grown SiO2/GaN interface

Abstract

An attempt was made to form a thermally grown SiO2/GaN interface. A Si layer deposited on the c-plane GaN surface was oxidized in an O2 atmosphere to form a SiO2 layer. The formation of SiO2 with a bandgap of 8.6 eV was confirmed by x-ray photoelectron spectroscopy. Metal–oxide–semiconductor diodes were fabricated and tested to characterize the interface by electrical measurements. The capacitance–voltage (C–V) characteristics measured at 1 MHz showed that a longer oxidation time resulted in a steeper slope. However, it was unavoidable that a bump in a C–V curve appeared after a long oxidation time. The electron trap distributions derived from C–V curves exhibited a discrete-level trap at 0.7 eV from the conduction band edge. This discrete-level trap was an acceptor-like trap that can be assigned to a Ga vacancy. An insufficient oxidation led to a high leakage current owing to the asperities of the residual polycrystalline Si layer. Although the leakage current was improved by extending the oxidation time, an excessively long oxidation time resulted in a slight increase in the leakage current. We cannot deny the possibility of the diffusion of Ga atoms into SiO2 during oxidation. Moreover, the cross-sectional transmission electron microscopy and energy-dispersive x-ray spectroscopy of a sample formed with an excessively long oxidation time indicated the formation of a Ga oxide interlayer without a severe disorder. Most possibly, the formation of the Ga oxide interlayer by excess oxidation improved the interface properties.

Atomic structure analysis of gallium oxide at the Al2O3/GaN interface using photoelectron holography

“…Therefore, in recent years, the control of the oxidation state of the interface and the atomic arrangement have been reported. 4,[19][20][21][22][23][24][25] In particular, the gallium oxide layer has been analyzed by X-ray photoelectron spectroscopy (XPS) 26,27) and observed by cross-sectional transmission electron microscopy (TEM). 9,[28][29][30][31] Although many crosssectional TEM observations have been reported, making a detailed analysis of the interface between the amorphous and crystalline layers is difficult because of the damage that occurred during the sample preparation and crystallization of the material; this damage was caused by electron beam irradiation of Al 2 O 3 /GaN.…”