Polarity Reversible Freestanding AlN Thin Film and Its Application in Schottky Diode

AlN with specific polarity, i.e., N-polar or Al-polar, plays a key role in optimizing the transport characteristics of the electronic devices, by tuning barrier height, accumulating interfacial charges, and so on. However, limited by materials fabrication processes, there is yet a simple method that can directly reverse the polarity of the same AlN thin film. Thus, no direct experimental evidence was reported on in situ polarity reverse-induced effects on the same AlN device. In this work, by employing a transfer bonding and flipping process, free-standing AlN films with controllable polarity were fabricated. Scanned probe measurements (SPMs) were used to characterize as-transferred AlN films’ polarity. Then, Schottky barrier diodes (SBDs) were built on the sample with different polarity and polarity-related transport characteristics were demonstrated. SBD with N-polar showed a 55% reduction in the specific ohmic contact resistance, 87% in the positive ON-resistance, and an increase in the current density by an order of magnitude. Importantly, the barrier height difference calculated from the current–voltage curves of the SBDs was consistent with the surface potential in SPM, providing clear evidence on the different AlN polarities that modulated the potential barrier between the metal–semiconductor contacts. Our work provides a simple and effective way to control the polarity in AlN thin film, which offers useful reference and potential application for III–nitrides-based power devices.