Showing papers by "Jun Suda published in 2002"

Growth of AlN(1120) on 6H-SiC(1120) by Molecular-Beam Epitaxy.

Abstract: AlN epitaxial growth on 6H-SiC substrates with the (110) face, which is parallel to the direction, has been investigated. AlN epitaxial layers were grown by molecular-beam epitaxy (MBE) using elemental Al and rf plasma-excited nitrogen (N*). The surface roughness of the AlN layers was relatively small (rms roughness of 0.98 nm). From the results of reflection high-energy electron diffraction (RHEED), AlN layers on 6H-SiC (1120) substrates were revealed to be grown toward the [110] direction, not toward the [0001] direction. AlN and 6H-SiC (110) had an exact epitaxial relationship, i.e., [110]AlN∥[110]SiC and [0001]AlN∥[0001]SiC. The polytype of the AlN layer was also discussed based on the results of microscopic Raman scattering spectroscopy.

Molecular-beam epitaxial growth of insulating AlN on surface-controlled 6H-SiC substrate by HCl gas etching

Abstract: Insulating AlN layers were grown on surface-controlled 6H–SiC subtrates by molecular-beam epitaxy (MBE) using elemental Al and rf plasma-excited nitrogen (N*). HCl gas etching was introduced as an effective pretreatment method of substrate for MBE growth of AlN. 6H–SiC substrates pretreated by HCl gas etching had no surface polishing scratches and an atomically flat surface. In addition, evident (∛×∛)R30° surface reconstruction was observed even before thermal cleaning. AlN layers grown on this substrate had no defects related to surface polishing scratches and excellent insulating characteristics.

First-order Raman spectra and lattice dynamics of a NdGaO 3 crystal

Abstract: The phonon-dispersion curves of the ${\mathrm{NdGaO}}_{3}$ crystal are calculated on the basis of a rigid-ion model by using the measured frequency values by Raman and infrared polarized spectroscopy at room temperature. The temperature dependence of the molar heat capacity of ${\mathrm{NdGaO}}_{3}$ is also calculated using the one-phonon density of states obtained from the phonon-dispersion curves. The first-order polarized Raman spectra of the ${A}_{1g}$ mode in the ${\mathrm{NdGaO}}_{3}$ crystal have been measured in the temperature range between 31 and 500 K. The temperature dependence for the linewidth of the ${A}_{1g}$ modes has been analyzed at 339 and 470 ${\mathrm{cm}}^{\ensuremath{-}1}$ by using the phonon-dispersion curves, and the calculated result reproduces the observed one in the temperature range 31--500 K. Thus, the temperature dependence of the linewidth of the ${A}_{1g}$ modes in the ${\mathrm{NdGaO}}_{3}$ crystal is approximately explained by the cubic anharmonic term in the expansion series of the crystal potential energy.

Effects of 6H-SiC surface reconstruction on lattice relaxation of AlN buffer layers in molecular-beam epitaxial growth of GaN

Abstract: Growth of GaN on on-axis 6H-SiC (0001)Si substrates with an AlN buffer layer was performed by molecular-beam epitaxy. The effects of SiC surface reconstruction on the lattice relaxation of AlN buffer layers and the crystalline quality of GaN layers were studied. High-temperature HCl-gas etching followed by HF chemical treatment resulted in an atomically flat SiC surface with a 1×1 structure. The AlN layer grown on the surface showed slow lattice relaxation. GaN grown on the AlN buffer layer exhibited the narrowest (0002) x-ray rocking curve of 70 arcsec and 107 cm−2 screw-type dislocation density, which was two orders of magnitude smaller than that of GaN grown on as-received substrates.

Scanning Capacitance and Spreading Resistance Microscopy of SiC Multiple-pn-Junction Structure

Abstract: Scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) of a SiC multiple-pn-junction structure are presented. The structure was grown by atmospheric-pressure chemical vapor deposition using silane, propane and hydrogen. Nitrogen and diborane were used for n- and p-type doping gases, respectively. The SCM and SSRM results are compared with those of secondary ion mass spectrometry (SIMS). The 0.2-µm-thick n-type layer and 0.3-µm-thick p-type layer with a doping level of 1.5 ×1017 cm-3 in the multiple pn-junction were clearly resolved by both SCM and SSRM as well as SIMS.

Epitaxial Growth of AlN on 6H-SiC (1120) by Molecular-Beam Epitaxy and Effect of Low-Temperature Buffer Layer

Abstract: Aluminum nitride (AlN) has been grown on 6H-silicon carbide (SiC) substrates with the non-polar (1120) face using rf plasma-assisted molecular-beam epitaxy (rf-MBE) Reflection high-energy electron diffraction (RHEED) revealed that AlN and 6H-SiC (1120) had an exact epitaxial relationship, ie, [1120]AlN[1120]SiC and [0001]AlN∥[0001]SiC From the result of microscopic Raman scattering spectroscopy, the stacking structure of the AlN epitaxial layer was suggested to be a 2H structure, not a 6H structure A directly grown AlN layer and layer with AlN low-temperature (LT) buffer layer were investigated based on atomic force microscopy (AFM) and X-ray diffraction (XRD)

First-order Raman spectra and lattice dynamics of a NdGaO3 crystal

Abstract: The phonon-dispersion curves of the NdGaO 3 crystal are calculated on the basis of a rigid-ion model by using the measured frequency values by Raman and infrared polarized spectroscopy at room temperature. The temperaturedependence of the molar heat capacity of NdGaO 3 is also calculated using the one-phonon density of states obtained from the phonon-dispersion curves. The first-order polarized Raman spectra of the A 1 g mode in the NdGaO 3 crystal have been measured in the temperature range between 31 and 500 K. The temperature dependence for the linewidth of the A 1 g modes has been analyzed at 339 and 470 cm - 1 by using the phonon-dispersion curves, and the calculated result reproduces the observed one in the temperature range 31-500 K. Thus, the temperature dependence of the linewidth of the A 1 g modes in the NdGaO 3 crystal is approximately explained by the cubic anharmonic term in the expansion series of the crystal potential energy.

Lattice Relaxation of AlN Buffer on Surface-Treated SiC in Molecular-Beam Epitaxy for Growth of High-Quality GaN

Abstract: The effects of SiC surface treatment on the lattice relaxation of AlN buffer layers and the crystalline quality of GaN layers grown on the buffer layers were studied. AlN buffer layers and GaN main layers were grown by plasma-assisted molecular-beam epitaxy on on-axis 6H-SiC (0001)Si substrates. High-temperature HCl-gas etching resulted in an atomically flat SiC surface with (√3×√3)R30° surface reconstruction, while HCl-gas etching followed by HF chemical treatment resulted in an atomically flat surface with (1×1) structure. The AlN layer grown on the (1×1) surface showed slower lattice relaxation. GaN grown on the AlN buffer layer exhibited a (0002) X-ray rocking curve of 70 arcsec and 107 cm−2 of screw-type dislocation density, which was superior than that of GaN grown on (√3×√3)R30° surface.