Leakage Current Paths in Isolated AlGaN/GaN Heterostructures

Electrical characterization of AlGaN/GaN heterojunctions isolated by Ar-implantation identified three conduction regimes. These include an Ohmic regime below 100 V associated with conduction across the implanted area itself as well as an exponential regime above 400 V associated with a conduction across the buffer or buried interfaces with the substrate. While the extraction of activation energies found an average of roughly 0.85 eV for the Ohmic regime, activation energies above 400 V were consistent with a Poole-Frenkel conduction mechanism. Variations in epitaxial structure, lateral and vertical electric field enabled the distinction between a conduction path in the top layers of the structure and a conduction path which is at least partially vertical across the structure. In addition, time-dependent measurements showed a capacitive effect for conduction across the buffer at room temperature. Having identified the performance limiting conduction path through the buffer layers, these experimental results can also be used as a tool for epitaxy assessment very early on in the production process.