N-polar gallium nitride doping by atomic layer deposition for improved electrical performance

Atomic layer deposition (ALD) is an excellent growth technique to achieve high-quality, high-uniformity, and highly conformal films with precise growth control at low (<400 °C) substrate temperatures. In this work, ALD was used to deposit low-resistance GaN layers on nitrogen-polar (N-polar) semi-insulating (S.I.) GaN substrates at 300 °C; film conductivity was significantly increased by adding a Si-precursor dose step immediately after the Ga-precursor step in the group III half-cycle and before the nitrogen-based plasma step in the group V half-cycle. Hall measurements revealed remarkably lower resistivities and five orders of magnitude increases in charge density in the Si-doped GaN films (∼3.5 × 1019 cm−3) relative to unintentionally doped films (∼2 × 1014 cm−3), with a Hall mobility of ∼30 cm2/V-s. Moreover, the charge density was further increased to 6.0 × 1019 cm−3 by utilizing a dual plasma process and a sub-saturation dosing of the Ga-precursor prior to the Si dose in the group III half-cycle. The sample surface remained smooth in most experiments.