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(a) Schematic structure of the analyzed Schottky diodes. To ensure a vertical current flow, an n-doped GaN layer is placed on bottom of a conventional AlGaN/GaN heterostructure. For the stress experiment, devices can be connected through terminals A and B (horizontal contact scheme), and A and C (vertical contact scheme). (b) Typical degradation kinetics measured by stressing the devices at −12 V. Both the horizontal and the vertical contact schemes give similar results. (c) Variation of the electric field within device structure with increasing reverse voltage level.
(a) and (b) I-V measurements taken before and after the stress at −15 V, 9800 s, on one of the analyzed samples, in the forward and reverse-bias regions. (c) C-V measurements taken on the same device during stress time.
(a) Variation of leakage current and peak capacitance measured during stress at −15 V on one of the analyzed samples. (b) C-V curves simulated by considering different concentrations of traps located in the GaN buffer, in proximity of the AlGaN/GaN interface.
(a) and (b) A schematic representation of the model used to explain the increase in leakage current (diagrams not in scale, the 3 nm GaN cap is not represented for simplicity). (c) Simulated variation in the leakage current of the analyzed devices induced by an increase in the concentration of shallow donor traps located at the AlGaN/GaN interface (without considering any modification in the conductivity of the AlGaN layer).
(a) Variation of the leakage current of several identical Schottky diodes submitted to stress at different voltage levels. (b) Dependence of the time for degradation (time necessary for a 50% increase in leakage current) on the electric field over the AlGaN barrier.
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