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.