No abstract

SiO 2 film deposition and subsequent high-temperature annealing resulted in the generation of a two-dimensional electron gas (2DEG) at Al(Ga)N/GaN hetero-interfaces, of which the 2DEG was originally fully depleted. The obtained mobilities and sheet carrier concentrations were over 1100 cm 2 /Vs and 3.0 × 10 12 cm -2 , respectively. Surface energy lowering, which is proof of the generated 2DEG, was observed by electron state analysis using hard X-ray photoelectron spectroscopy. This damage-less method that selectively generates a 2DEG can contribute not only toward improving some characteristics in existing devices but also toward creating entirely novel devices.

The growing demand for power devices has led to the use of magnetic field-applied Czochralski (m:Cz) wafers owing to the limited production capacity and available diameters of the traditionally used floating zone (FZ) wafers. Consequently, the influence of oxygen impurities in the wafers on the electrical properties of devices, regardless of the growth method, needs to be investigated to achieve a stable fabrication process for power devices. Using the proton irradiation doping process and spreading resistance profiling technique, we evaluated the effective diffusion coefficient (Deff) related to trap-limited diffusion of hydrogen and the effects of impurities on diffusivity. We irradiated n-type silicon wafers, which have different carbon, oxygen, and phosphorus concentrations, with 2 MeV protons and annealed them at 300–400 °C. By analyzing the width of the n-type region, where hydrogen-related shallow donors (HDs) are induced, we estimated Deff to be five to six orders of magnitude lower than the intrinsic diffusion coefficient, indicating that hydrogen motion is highly trap-limited. Deff was significantly dependent on the oxygen concentration, and the activation energy of hydrogen diffusion varied from 0.57 ± 0.15 eV (pure epitaxial wafer) to 2.19 ± 0.15 eV (m:Cz wafer). This trend suggests that oxygen-related defects preferentially trap the mobile hydrogen released from thermally dissociated HDs. This study also reveals that the diffusion coefficients of different materials when annealed at 400 °C are comparable. This information is essential to realize the cost-effective production of power devices because we can treat m:Cz and FZ wafers equivalently during the doping process.

Ideal transport characteristics were firstly demonstrated in AlGaN/GaN Schottky barrier diodes (SBDs) on free-standing SI-GaN substrate. This result indicates that unintentional doping levels due to the dislocations and defects were drastically reduced in the fabricated SBDs on SI-GaN substrate.