Effect of threading dislocation in an AlN nucleation layer and vertical leakage current in an AlGaN/GaN high-electron mobility transistor structure on a silicon substrate

We used conductive atomic force microscopy (C-AFM) and aqueous potassium hydroxide (KOH) solution etching to investigate the origin of vertical leakage current through an AlN nucleation layer in AlGaN/GaN high-electron mobility transistors (HEMTs) grown on a Si substrate. The micro area vertical leakage current in the AlN nucleation layer was observed in the presence of large hexagonally shaped etch pits (Each etch pit was about 1 μm in diameter) using C-AFM measurements after KOH etching. It is considered that large hexagonally shaped etch pits originate from screw-type dislocations from the etch pit shape. Vertical leakage current in the AlN nucleation layer increased by two orders of magnitude with increasing density of large hexagonally shaped etch pits in the AlN nucleation layer. Consequently, with increased vertical leakage current in the AlN nucleation layer, the vertical leakage current in the HEMT structure also increased. These results indicate that screw-type threading dislocations in AlN nucleation layers creates the vertical leakage current path in HEMT structures on Si substrates.