Forward current transport and noise behavior of GaN Schottky diodes

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In this work, we first measure the forward temperature-dependent current-voltage (<i>T</i>-<i>I</i>-<i>V</i>) characteristics of the GaN-based Schottky diodes grown on the bulk GaN substrates, and then study the transport mechanisms of the forward current and the low-frequency current noise behaviors under various injection levels. The results are obtained below. 1) In a forward high-bias region the thermionic emission current dominates, and the extracted barrier height is about 1.25 eV at <i>T</i> = 300 K, which is close to the value measured by capacitance-voltage sweeping. 2) In a forward low-bias region (<i>V</i> < 0.8 V) the current is governed by the trap assist tunneling process, having an ideality factor much larger than 1, and the derived barrier height is about 0.92 eV at <i>T</i> = 300 K, which indicates that the conductive dislocation should be mainly responsible for the excessive leakage current, having a reduced barrier around the core of dislocations. 3) The Lorentzian noise appears only at very small current (<i>I</i> < 1 μA) and low frequency (<i>f</i> < 10 Hz), whose typical time constant is extracted to be about 30 ms, depending on the multiple capture and release process of electrons via defects. 4) At a higher frequency and current, the low-frequency 1/<i>f</i> noise becomes important and the corresponding coefficient is determined to be about 1.1, where the transport is affected by the random fluctuation of the Schottky barrier height.