Identification and elimination of inductively coupled plasma-induced defects in Al_xGa_1-xN/GaN heterostructures

By using temperature-dependent Hall, variable-frequency capacitance—voltage and cathodoluminescence (CL) measurements, the identification of inductively coupled plasma (ICP)-induced defect states around the Al_xGa_1-xN/GaN heterointerface and their elimination by subsequent annealing in Al_xGa_1-xN/GaN heterostructures are systematically investigated. The energy levels of interface states with activation energies in a range from 0.211 to 0.253 eV below the conduction band of GaN are observed. The interface state density after the ICP-etching process is as high as 2.75×10¹² cm^-2·eV^-1. The ICP-induced interface states could be reduced by two orders of magnitude by subsequent annealing in N₂ ambient. The CL studies indicate that the ICP-induced defects should be Ga-vacancy related.