Showing papers by "Tsutomu Uesugi published in 2011"

Study of etching-induced damage in GaN by hard X-ray photoelectron spectroscopy

Abstract: We carried out nondestructive measurements of the depth profile of etching-induced damage in p-type gallium nitride (p-GaN), in particular surface band bending, using Hard X-ray Photoelectron Spectroscopy (HAX-PES). HAX-PES at different take-off angles of photoelectrons made it clear that etching by inductively coupled plasma (ICP) introduced donor-like states in a surface layer of GaN. We were able to quantitatively analyze band bending and charge distribution in an etched p-GaN. The analysis results indicated the existence of deep donors with a concentration of 1―2 x 10 20 cm ―3 in a surface layer whose thickness increased with increasing a bias power of ICP.

Study on leakage current of pn diode on GaN substrate at reverse bias

Abstract: In this paper, we studied on a leakage current of a pn diode on a GaN substrate isolated by a mesa structure at a reverse bias. The leakage current flowed at a surface of the mesa sidewall across the pn junction. Results of scanning capacitance microscopy and scanning spread resistance microscopy indicated that the surface of the mesa sidewall in the p type region changed to a depleted or a n--layer. Results of auger electron spectroscopy indicated that a concentration of nitrogen decreased near the surface of the mesa sidewall. From these results, we estimated the leakage current was caused by a change of the p type region at the surface of the mesa sidewall to the depleted or n--layer by inductively coupled plasma dry etching, which was used to form the mesa structure. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Automotive Applications of GaN Power Devices

Abstract: Many power switching devices are used in a hybrid vehicle (HV) and an electric vehicle (EV). The power electronics in the HV/EV system is reviewed. For future development of the HV/EV system, higher performances of the power devices than Si limit, for example, low on-resistance, high operation temperature, are strongly required. GaN power devices are promising candidate for the requirements. Developing GaN power devices are lateral structure and vertical structure. Recent progress of the GaN power devices are also reviewed.

Hole traps in n‐GaN detected by minority carrier transient spectroscopy

Abstract: Minority carrier transient spectroscopy (MCTS) has been applied for the detection of hole traps in n-GaN using Schottky diodes. MCTS using 355 nm light emitting diodes is performed under isothermal conditions in the temperature range 280 to 330 K for n-GaN grown by metalorganic chemical vapor deposition on sapphire. Isothermal MCTS spectra reveal the Ev + 0.86 eV hole trap with the trap concentration of 1.1x1016 cm-3. The Ev + 0.86 eV hole trap has the higher concentration as compared to electron traps observed by deep level transient spectroscopy. Thus, the isothermal MCTS around room temperature provides a convenient way to evaluate the dominant trap in n-GaN. It is suggested that the Ev + 0.86 eV hole trap is associated with the VGa-related defect or carbon-related defect. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Parallel connection dc-dc converter

Abstract: PROBLEM TO BE SOLVED: To provide a technology of effectively suppressing surge voltages and noises, while utilizing superior characteristics of a lateral GaN MOS high electron mobility transistor SOLUTION: A parallel connection DC-DC converter 100a is provided which is used for a moving-body mounting type power supply system to supply an electric power to a device to drive a moving body, and has a boosting ratio of 4 or more The parallel connection DC-DC converter 100a includes three DC-DC converter units 111, 112, 113 connected in parallel with one another Each DC-DC converter unit includes switching elements 511, 512, 513 including a lateral type high electron mobility transistor using GaN as a material and reactors 121, 122, 123 connected in series to the switching elements thereof COPYRIGHT: (C)2011,JPO&INPIT

Semiconductor device including p-type group iii nitride semiconductor layer, and method for manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To solve the problem in which when a plurality of semiconductor devices are manufactured utilizing a laminate structure including a p-type group III nitride semiconductor layer, subjected to etching and other process and divided into individual semiconductor devices, a leak current flows along a surface of the p-type group III nitride semiconductor layer exposed on a side surface of the individual semiconductor devices.SOLUTION: A method for manufacturing a semiconductor device including a p-type group III nitride semiconductor layer 8, comprises: etching or dicing a laminate structure including the p-type group III nitride semiconductor layer 8 from a front surface or a back surface thereof to a depth not reaching the p-type group III nitride semiconductor layer 8; and dividing the laminate structure into individual semiconductor devices by cleaving the remaining thickness. The surface of the p-type group III nitride semiconductor layer 8 exposed on a side surface of the semiconductor device forms a cleavage surface having reduced crystal defects, thus preventing a leak current from flowing along the side surface.

Electrical Characterization of GaN p-n Junctions Grown on Freestanding GaN Substrates by Metal-Organic Chemical Vapor Deposition

Abstract: The electrical characteristics of GaN p–n junctions grown on freestanding GaN substrates by metal–organic chemical vapor deposition were investigated. The current–voltage (I–V) characteristics of the GaN p–n diode showed relatively low values and, little temperature dependence of the reverse leakage current. The breakdown voltage of the GaN p–n diode was 900 V and the leakage current at 600 V was 1 µA/cm2 or less. The inverse of squared capacitance–voltage (1/C2–V) data showed a linear relationship, indicating an abrupt junction at the p–n interface. Little temperature dependence of the C–V curve was also observed. Plasma etching before the growth of the p-GaN layer induced a large leakage current and a lower breakdown voltage, probably due to the disorder of atomic bonds and the nitrogen depletion at the plasma-etched surface. The insertion of a regrown n-GaN layer between the p-GaN and the plasma-treated n-GaN surface was effective in suppressing the leakage current and recovering the breakdown voltage.