M. Shimizu

Realization of Ga-polarity GaN films in radio-frequency plasma-assisted molecular beam epitaxy

GaN heteroepitaxial growth on sapphire (0 0 0 1) substrates was carried out by radio-frequency (RF) plasma-assisted molecular beam epitaxy. The lattice polarity of RF-MBE-grown GaN lms on sapphire (0 0 0 1) substrates was investigated as a function of bu!er layer process. GaN lms with Ga-face lattice polarity were fabricated using an AlN high-temperature bu!er layer before GaN growth. Direct measurements by coaxial impact collision ion scattering spectroscopy, as well as re#ection high-energy electron di!raction, scanning electron microscope observations of surface morphologies and chemical etching, conrmed the polarity assignment. Realization of Ga-polarity lms on sapphire substrates by RF-MBE is a promising result and is expected to lead to a breakthrough in fabricating high-quality MBE-grown III-nitride lms for device applications. ( 2000 Elsevier Science B.V. All rights reserved.

Growth and characterizations of AlGaN/GaN heterostructures using multi-AlN buffer layers in plasma-assisted molecular beam epitaxy

Abstract AlGaN/GaN single heterostructures (SH) were grown on sapphire (0xa00xa00xa01) substrates by plasma-assisted molecular beam epitaxy. It was found that multi-AlN buffer layers are effective to improve the two-dimensional electron gas (2DEG) mobility. High 2DEG mobility of about 1200xa0cm 2 /Vxa0s at room temperature was obtained by inserting 4 periods of AlN buffer layers. It is considered that the improvement resulted from the reduction of dislocations in the films by the multi-AlN buffer layers. It was also found that when the periods of the AlN buffer layer were 6, cracks were generated on the surface resulting in a reduction of the mobility.

High Breakdown Voltage AlGaN/GaN MIS-HEMT with SiN and TiO/sub 2/ Gate Insulator

We report the fabrication of AlGaN/GaN high electron mobility transistor (HEMT) with high breakdown voltage by employing the metal-insulator-semiconductor (MIS) gate structure. SiO 2 , SiN, and TiO 2 were used for the insulators. The gate leak current was significantly reduced by employing the MIS structure, and the breakdown voltage characteristics were improved. The breakdown voltage of the MIS-HEMTs increased non-linearly with the increase of gate-drain length L gd . The TiO 2 insulator exhibited highest breakdown voltage of 2 kV with the on-resistance of 15.6 mΩ cm 2 .for L gd = 28 μm. On the other hand, the breakdown voltage and on-resistance for SiN MIS-HEMT were found to be 1.7 kV and 6.9 mΩ cm 2 , respectively. We demonstrated that AlGaN/GaN MIS-HEMTs are promising not only for high speed applications but also for high power switching applications.

GaN/AlN Resonant Tunneling Diode with High Peak-to-Valley Current Ratio Grown by Metal-Organic Vapor Phase Epitaxy

We report a high-quality GaN/AlN resonant tunneling diode (RTD) grown by metal-organic vapor phase epitaxy (MOVPE). A negative differential resistance with a high peak-to-valley current ratio (PVCR) of 28 was obtained by optimizing the device design and growth conditions. This PVCR is much higher than that for a previous GaN/AlN RTD grown by MOVPE, and is also equivalent to the highest PVCR obtained for a device grown by molecular beam epitaxy. Thus, MOVPE growth is also shown to be effective for the fabrication of high-quality GaN/AlN RTDs.

Reduction of current collapse in AlGaN/GaN HEMTs using thick GaN cap layer

1 Department of Electrical Engineering, Faculty of Science and Technology, Tokyo University of Science. 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan Advanced Power Electronics Center, AIST, Central 2, 1-1-1, Umezono, Tsukuba, Ibaraki 305-8568, Japan +Phone +81-29-861-5647 E-mail: mitsu.shimizu@asit.go.jp Leading Edge Technology Development Department, Taiyo Nippon Sanso Corporation, 10 Okubo, Tsukuba, Ibaraki 300-2611, Japan