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 (N
_C
= 10
¹⁸
cm
^-3
) and high (N
_C
= 10
¹⁹
or N
_C
= 7 × 10
¹⁹
cm
^-3
) carbon concentration N
_C
. The discharging and charging events are found to be governed by transport properties of GaN:C for whole N
_C
range. However, distinct temperature behavior has been found as a function of N
_C
. In the samples with low N
_C
, 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 N
_C
, 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 ≥ 10
¹⁹
cm
^-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 N
_C
= 10
¹⁸
cm
^-3
where 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 N
_C
and dislocation densities, as well as for reliability testing and defect analysis.