Kelvin probe force microscopy study of surface potential transients in cleaved AlGaN∕GaN high electron mobility transistors

The surface potential of cleaved cross sections of AlGaN∕GaN high electron mobility transistors was measured by Kelvin probe force microscopy. For the bias conditions of Vgs=−5V and Vds=20V, the electric field was concentrated near the GaN∕SiC interface under the gate and between the gate and drain electrodes. A negative potential that decreased over time was observed in the GaN layer beginning 10min after the bias stress was removed. The transient surface potential was found to be well described by an exponential dependence with two time constants: 11 and 55s.