Influence of Surface States in AlGaN/GaN Nanodiodes Analyzed by Preconditioned Transient Current Measurements

AlGaN/GaN nanodiodes consisting of an array of several nanochannels in parallel are potential candidates for detection in the terahertz (THz) range. The nanochannels are fabricated by etching two isolating trenches and show a current-voltage characteristic strongly influenced by the presence of surface charges at the channel sidewalls. Transient current effects have been characterized at room temperature and found to be associated with electron capture and emission mechanisms by surface traps. The conductance of these devices increases or decreases depending on the history of applied voltage since it changes the occupation of the surface states and thus the depletion region present near the sidewalls. Moreover, the lateral field effect plays an important role, since, in addition to promoting trap charging or discharging, modifies the depletion region around the trenches, both of these processes determine the conductance of the channel. In addition, the increase of the bias induces an effect analog to the drain-induced barrier lowering (DIBL) of FETs. In this article, the static behavior and transients of current of these nanochannels were characterized from the experimental point of view thanks to very short duration voltage pulses, while Monte Carlo (MC) simulations were able to mimic the observed trends providing as well a physical interpretation that the charges trapped at the sidewalls of the trenches of the channels act as the gate in a FET.