Tetsu Kachi 교수

Many power switching devices are used in hybrid vehicles (HVs) and electric vehicles (EVs). To improve the efficiency of HVs and EVs, better performance characteristics than those of Si power devices, for example, lower on-resistance, higher speed, higher operation temperature, are required for the power devices. GaN power devices are promising candidates for satisfying the requirements. A lateral GaN power device with a blocking voltage of 600 V and a vertical GaN power device with a blocking v

Abstract Magnesium ion implantation has been performed on a GaN substrate, whose surface has a high thermal stability, thus allowing postimplantation annealing without the use of a protective layer. The current–voltage characteristics of p–n diodes fabricated on GaN showed distinct rectification at a turn-on voltage of about 3 V, although the leakage current varied widely among the diodes. Coimplantation with magnesium and hydrogen ions effectively suppressed the leakage currents and device-to-d

A new buffer layer to grow high-quality GaN films was proposed. The new buffer layer consisted of a thin (20–30 nm) InN layer deposited at low temperature (∼600 °C). GaN films were grown on (112̄0)-oriented (A-face) sapphire substrates using a conventional GaN buffer layer and an InN buffer layer by atmospheric pressure metalorganic vapor phase epitaxy. Dislocations in the GaN films were observed by cross-sectional transmission electron microscopy (TEM). The dislocation densities were measured f

Abstract Sources of carrier compensation in n-type and p-type GaN layers grown by metalorganic vapor phase epitaxy were quantitatively identified by a combination of Hall-effect analysis and deep level transient spectroscopy. For n-type GaN, we identified three electron compensation sources: residual carbon atoms likely sitting on nitrogen sites (C N ), an electron trap at the energy level of E C –0.6 eV (the E3 trap), and self-compensation appearing with increasing donor concentration. We showe

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead o

Many power switching devices are used in a hybrid vehicle (HV) and an electric vehicle (EV) systems. For future development of the HV/EV, higher performances than Si power device, for example, low on-resistance, high speed, high operation temperature, are strongly required. GaN power devices are promising candidate for the requirements. Present status of the GaN power device development is presented. Reliability of the GaN power device was also discussed.

To investigate Mg diffusion during ultra-high-pressure annealing, which activates Mg acceptors in GaN, GaN samples with p–n junctions prepared via epitaxial growth were annealed at 1573 K under 1 GPa. The profiles of Mg diffusion toward the underlying n-type layer cannot be explained by a simple diffusion model. We found that H atoms diffused along with Mg atoms. By considering the suppressed diffusion of positively charged interstitial H atoms due to the electric field in the depletion layer, w

The performance of GaN power devices has been rapidly improving. Recently, the main approach is the use of AlGaN/GaN HEMT structures on Si substrates, for which the target breakdown voltage is initially 600V or less. Although issues still remain with regard to current collapse and the threshold voltage required for normally-off operation, many companies have announced their intention to commercialize such devices. In this report, recent developments concerning GaN power devices are reviewed, and