Showing papers by "Jun Suda published in 2003"

4H-polytype AlN grown on 4H-SiC(112̄0) substrate by polytype replication

Abstract: 4H-polytype AlN has been grown on a 4H-SiC substrate with the (1120) face via plasma-assisted molecular-beam epitaxy The microscopic structure of the AlN/4H-SiC interface was examined using high-resolution transmission electron microscopy, and the polytype replication of the 4H structure from the 4H-SiC(1120) substrate was evidently confirmed The x-ray rocking curve of (1120) diffraction for the single crystalline 4H-AlN epilayer exhibited a very small linewidth of 90 arc sec, suggesting noticeably small tilting around the [1120] direction The excellent crystalline quality is probably owing to the polytype matching between the 4H-AlN epilayer and the 4H-SiC substrate, which resulted in remarkable reduction of defects at the interface

High-Quality AlN by Initial Layer-by-Layer Growth on Surface-Controlled 4H–SiC(0001) Substrate

Abstract: The initial layer-by-layer growth of AlN was realized on a surface-controlled 4H–SiC(0001) substrate using plasma-assisted molecular-beam epitaxy (PA-MBE). To achieve initial two-dimensional (2D) growth, the control of SiC surface chemistry is very important as well as that of surface flatness. The effect of SiC preparation on the surface structure and chemical composition was investigated by using reflection high-energy electron diffraction (RHEED) and in situ X-ray photoelectron spectroscopy (XPS). The initial growth mode of AlN was strongly influenced by the removal of residual oxygen atoms from the SiC surface. Symmetrical and asymmetrical X-ray rocking curve (XRC) measurements revealed that initial 2D growth was essential to obtain the excellent crystalline quality of AlN layer.

ZrB2 Substrate for Nitride Semiconductors

Abstract: Zirconium diboride (ZrB2) has excellent properties as an electrically conductive substrate for nitride semiconductors. In this paper, the bulk growth of ZrB2 by a floating-zone method and some properties of ZrB2, together with a brief summary of heteroepitaxial growth of gallium nitride (GaN) by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE), are presented. By optimizing the bulk growth conditions, a 20-mm-diameter ZrB2 single crystal was obtained. The cleavage direction of the ZrB2 (0001) substrate was confirmed to be parallel to [1120], which is parallel to that of GaN (0001). Epitaxial growth by both MBE and MOVPE was demonstrated. The grown n-type GaN/ZrB2 structure exhibited ohmic-like current–voltage behavior. These results indicate that ZrB2 has potential for application to the substrate for nitride semiconductors.

The First-Order Raman Spectra and Lattice Dynamics for YAlO3 Crystal

Abstract: The phonon-dispersion curves of the YAlO 3 crystal are calculated on the basis of a rigid-ion model using the measured frequency values by Raman and infrared polarized spectroscopy at room temperat...

Lattice dynamics and temperature dependence of the first-order Raman spectra for α-SiO2 crystals

Abstract: The phonon dispersion curves for α-SiO2 crystals were calculated on the basis of a rigid-ion model. The first-order Raman spectra of the A1 mode of the α-SiO2 crystal were measured in the temperature range from 303.1 to 773.1 K. The temperature dependence of the linewidth was analyzed by using the phonon dispersion curves, and the results showed that it was caused approximately by the cubic anharmonic term in the crystal potential energy. The temperature dependence of the frequency shift of the A1 mode was analyzed by using the lattice dynamic perturbative treatment. We found that the quartic anharmonic term of the first-order perturbation and also the cubic term of the second-order perturbation contribute to the temperature dependence of the frequency shift of the A1 mode in the α-SiO2 crystal. Copyright © 2003 John Wiley & Sons, Ltd.

Fabrication of SiC lateral super junction diodes with multiple stacking p- and n-layers

Abstract: Using epitaxial multiple p-n junction structures of 4H-SiC, lateral super junction diodes were fabricated for the first time. The breakdown voltage of the device was 400 V, which is more than 3/spl times/ higher than the theoretical value calculated for a device with uniformly-doped drift layer (130 V), indicating the effective operation of the super junction structure.

Impact of SiC surface control on initial growth mode and crystalline quality of AlN grown by molecular-beam epitaxy

Abstract: The surface pretreatment of SiC substrate for AlN heteroepitaxial growth was investigated to realize initial two-dimensional (2D) layer-by-layer growth. AlN layers were grown on atomically flat SiC (0001) substrates by plasma-assisted molecular-beam epitaxy (PA-MBE). To achieve initial 2D growth, the control of SiC surface chemistry was very important as well as that of surface flatness. Owing to Ga deposition on the SiC surface and subsequent flash-off, an oxygen-free () R30° surface structure was achieved, and initial 2D growth with an evident RHEED intensity oscillation was demonstrated. The initial growth mode of AlN closely correlated with the crystalline quality of AlN layer. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of high-quality non-polar AlN on 4H-SiC(11–20) substrate by molecular-beam epitaxy

Abstract: Non-polar AlN epitaxial growth on SiC substrates with the (11–20) face, which is parallel to the 〈0001〉 direction, has been investigated. AlN(11–20) epilayers were grown on 6H- and 4H-SiC(11–20) substrates by molecular-beam epitaxy (MBE) using elemental Al and rf plasma-excited nitrogen. The crystalline structure of the AlN layer was strongly influenced by the stacking structure of the SiC substrate. A considerably smooth AlN(11–20) layer with an rms roughness of 0.3 nm was obtained on the 4H-SiC(11–20) substrate. From the results of X-ray diffraction (XRD), the superior crystalline quality of the AlN(11–20) layer on the 4H-SiC(11–20) substrate was clearly shown.

Surface Control of ZrB2 (0001) Substrate for Molecular-Beam Epitaxy of GaN

Abstract: Zirconium diboride (ZrB2) is a promising lattice-matched substrate for GaN-based materials. A key issue to realize high-quality heteroepitaxial growth is preparation of the substrate surface. The ZrB2 surface was studied by x-ray photoemission spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). XPS results indicated the presence of both ZrO2 and ZrB2 on the as-received substrate surface. Thermal cleaning at 1000°C in ultra-high vacuum, Ar+ ion sputtering, and wet chemical treatments were examined as surface preparation methods. After treatment with HF acid, the O peak intensity was much reduced. The combination of HF treatment and thermal cleaning resulted in sharp and intense RHEED from the ZrB2 surface. GaN grown on the surface by molecular-beam epitaxy exhibited intense photoluminescence, suggesting that this treatment is effective to obtain high-quality GaN on ZrB2 substrates.

Either step-flow or layer-by-layer growth for AlN on SiC (0001) substrates

Abstract: AIN was grown on 4H- or 6H-SiC (0001) on-axis substrates by plasma-assisted molecular beam epitaxy. By utilizing optimized SiC surface pretreatment, RHEED oscillations just after the growth of AIN were obtained with high reproducibility. This study focused on the growth kinetics of AIN and the correlation between kinetics and the crystalline quality of the grown layers. It was found that the growth mode changed from layer-by-layer to step-flow for high growth temperatures, while for lower temperatures the layer-by-layer growth mode persisted. The mechanism responsible for the change in growth mode is discussed. Symmetrical (0002) and asymmetrical (01–14) x-ray rocking curve measurements were carried out to evaluate the crystalline quality. For the (0002) peak, both high-temperature and low-temperature grown layers showed almost the same FWHM values. On the other hand, for the (01–14) peak, the FWHM of low-temperature grown AIN was much smaller (180 arcsec) than that of the high-temperature grown AIN (450 arcsec).