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Buffer leakage in aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure transistors is recognized as an issue that has deleterious consequences on device performance for high-power, high-frequency transistors and has been related to the presence of uncharged threading screw dislocations. In this study, we demonstrate that measurements of buffer leakage in AlGaN/GaN heterostructures grown on bulk gallium nitride (GaN) substrates are consistent with a mechanism based on the concept of dislocations acting as quantum wires in series with unintentional silicon (Si) impurity incorporation at the bulk GaN substrate/GaN buffer interface. The number of electronic channels N deduced from the leakage data using Landauer’s formula for the quantum resistance of N electronic channels is consistent with the number of dislocations along the ohmic contact pads determined from panchromatic cathodoluminescence and x-ray diffraction measurements of the dislocation density. This mechanism is consistent with Shockley’s suggestion that dislocations can act as one-dimensional conductors due to the presence of edge states along the dislocation core.
In an effort to investigate the stability of the surface and hetero-interface of AlGaN/GaN HEMTs during high temperature device processing steps, AlGaN/GaN HEMT samples were subjected to temperatures from 650°C to 1150°C for a period of 30 seconds prior to processing. Hall and photoluminescence measurements were performed on samples before and after temperature stressing. The samples annealed at 700°C and 1150°C were then processed, and electrical parametric data were collected during and after processing. Large increases in HEMT Schottky gate diode reverse leakage current are observed at higher pre-process annealing temperatures, while the low-field mobility decreases.
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