Electronic transport through GaN/AlN single barriers: Effect of polarisation and dislocations

In this work, we study electronic and conduction properties of a single AlN barrier (thickness from 0.5 to 5 nm) embedded in GaN. The electronic structure was simulated using a self-consistent Schrodinger-Poisson solver, and verified by photoluminescence (PL) measurements. For 0.5- and 1-nm-thick barriers, we can identify the PL line related to recombination from the first electron confined level at the bottom interface of the barrier to the first hole confined level at the top interface. The PL evolution with bias reveals that most of the applied voltage drops in the depleted cap layer. Carrier transport was studied using conductive atomic force microscopy (C-AFM). Reference GaN layers display a rectifying behaviour between the C-AFM tip and the GaN surface. In samples with a barrier thickness from I to 3 nm, blockage by the barrier results in negligible current under direct bias, except for hot spots at dislocations (density similar to 1 X 10(7) cm(-2)). Finally, in samples with 5-nm-thick AIN barriers, a high-current density appears at reverse bias, which assigned to defects induced by AlN relaxation, as verified by transmission electron microscopy. (C) 2008 Elsevier Ltd. All rights reserved.