Effect of Carbon Doping on Charging/Discharging Dynamics and Leakage Behavior of Carbon-Doped GaN

Capacitance transient spectroscopy and dc current-voltage (I-V) characterization are employed to analyze charging/discharging effects and transport in 200-nm-thin carbon-doped GaN layers (GaN:C) with a low (NC= 1018cm-3) and high (NC= 1019or NC= 7 × 1019cm-3) carbon concentration NC. The discharging and charging events are found to be governed by transport properties of GaN:C for whole NCrange. However, distinct temperature behavior has been found as a function of NC. In the samples with low NC, an Arrhenius-like behavior with an activation energy of 0.8 eV indicates that the hole transport in valence band (VB) is the limiting process and the carrier exchange occurs between VB and the defect level. In contrast, in samples with high NC, a non-Arrhenius charging/discharging behavior with exp(aT)-dependence (a being a constant) in a wide temperature range (150-560 K) indicates that the transport is governed by defect bands (DBs) where the carrier exchange occurs between DBs and the carbon defect level. For samples with NC ≥ 1019cm-3, the large charge accumulation in GaN:C produces a large energy barrier to prevent electron injection from n-GaN to GaN:C, thus making GaN:C blocking. This is in contrast to samples with NC= 1018cm-3where the barrier is low, rendering thus the bilayer leaky. Detailed physical models for carrier capture and emission processes and carrier transport are provided for both cases. The developed knowledge is important for understanding the role of growth parameters such as NCand dislocation densities, as well as for reliability testing and defect analysis.