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Abstract
We report on the electrical properties of the AlN/4H-SiC interface using capacitance- and conductance-voltage (CV and GV) analysis of AlN/SiC MIS capacitors. The crystalline AlN layers are made by hot wall MOCVD. CV analysis at room temperature reveals an order of magnitude lower density of interface traps at the AlN/SiC interface than at nitrided SiO2/SiC interfaces. Electron trapping in bulk traps within the AlN is significant when the MIS capacitors are biased into accumulation resulting in a large flatband voltage shift towards higher gate voltage. This process is reversible and the electrons are fully released from the AlN layer if depletion bias is applied at elevated temperatures. Current-voltage (IV) analysis reveals that the breakdown electric field intensity across the AlN dielectric is 3–4 MV/cm and is limited by trap assisted leakage. By depositing an additional SiO2 layer on top of the AlN layer, it is possible to increase the breakdown voltage of the MIS capacitors significantly without having much impact on the quality of the AlN/SiC interface.
Highlights
4H-Silicon carbide (SiC) can be thermally oxidized to yield its native silicon dioxide (SiO2) but the drawback is a rather poor interface quality of the SiO2/SiC interface
The flatband voltage is ∼0.7 V which is close to the theoretical flatband voltage (i.e. ∼0.4 V) which shows that initially the AlN layer contains insignificant amount of fixed charge
It is evident that the interface traps that are held responsible for electron channel mobility reduction in 4H-SiC MISFETs are practically absent at the AlN/SiC interface in this study
Summary
4H-Silicon carbide (SiC) can be thermally oxidized to yield its native silicon dioxide (SiO2) but the drawback is a rather poor interface quality of the SiO2/SiC interface. The quality of the SiO2/SiC interface has been improved by various oxidation and nitridation methods which has enabled the commercialization of high voltage (> 900 V) MOSFETs [1,2,3]. These high voltage devices can tolerate lower channel mobilities than the low voltage ones because the current there is limited by the resistance of the low doped SiC used in these devices. SiC MISFETs with crystalline AlN as a gate dielectric grown by molecular beam epitaxy (MBE) have been reported but the structures were leaky and the channel mobility was very low (< 1 cm2/Vs) [10]. A crystalline AlN has been grown by MOCVD on both 4H- and 6H-SiC but studies showed a high density of fixed charge within the AlN and high density of interface traps [8,16]
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