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.
Highlights
GaN is a promising material for fabricating highly efficient power electronic devices because of its wide bandgap (3.4 eV),1 high breakdown field (3.3 MV/cm),2 high electron mobility (1000 cm2/V s),1 high saturation electron velocity (2.6 × 107 cm/s),3 and good thermal conductivity (2.1 W/cm ○C).1 Recently, it has become possible to obtain a high-quality GaN layer with low dislocation density by epitaxial growth on GaN substrates, enhancing the advantage of this material
Since a relatively high temperature (>800 ○C) process can be applied to GaN MOS structures,7 the thermal growth of SiO2 on GaN is a candidate method to form the SiO2/GaN interface
Bumps in C–V curves appeared for the long oxidation time
Summary
GaN is a promising material for fabricating highly efficient power electronic devices because of its wide bandgap (3.4 eV), high breakdown field (3.3 MV/cm), high electron mobility (1000 cm2/V s), high saturation electron velocity (2.6 × 107 cm/s), and good thermal conductivity (2.1 W/cm ○C). Recently, it has become possible to obtain a high-quality GaN layer with low dislocation density by epitaxial growth on GaN substrates, enhancing the advantage of this material. The metal–oxide–semiconductor (MOS) structure formed on a GaN-on-GaN layer exhibits excellent electrical properties with minimal interface states.. The metal–oxide–semiconductor (MOS) structure formed on a GaN-on-GaN layer exhibits excellent electrical properties with minimal interface states.4–7 This property enables the realization of a high-efficiency high-power MOS fieldeffect transistor (FET) that fully derives the excellent properties from GaN. SiO2 thermally grown on Si by dry oxidation forms an excellent insulator–semiconductor interface. If a method of forming an excellent interface between thermally grown SiO2 and GaN is available, a MOSFET with excellent performance can be expected. Since a relatively high temperature (>800 ○C) process can be applied to GaN MOS structures, the thermal growth of SiO2 on GaN is a candidate method to form the SiO2/GaN interface. We attempted to form a thermally grown SiO2/GaN interface
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