Removal of Si impurities from GaN regrowth interfaces using XeF2

Abstract

We present a process to decrease the concentration of unintentional impurities incorporated at GaN regrowth interfaces in situ by combining both cycles of Ga adsorption and desorption (“Ga polishing”) and room temperature XeF2 exposure. Schottky diodes and MOS structures were fabricated on GaN grown on freestanding GaN (FS-GaN) layers with an intentional ambient exposure in the drift region for the purpose of CV depth profiling. These layers were then either immediately regrown on or treated with just Ga polishing, or a combination of Ga polishing and XeF2 exposure, to remove the O, C, and Si that were incorporated at the regrowth interface due to the ambient exposure. The layers that received both Ga polishing and XeF2 treatment showed a reduction in net donor sheet density (ND-NA), measured by CV, by nearly an order of magnitude (from ∼5 × 10−12 to ∼5 × 10−11 cm−2). SIMS analysis corroborates this charge reduction with a reduction in the Si sheet concentration at this interface. The results provide an in situ processing method for vertical GaN devices, including regrown p–n junctions, for reducing the concentration of unintentional impurities at regrowth interfaces.