Hideo Nakanishi

Suppression of crack generation in GaN epitaxy on Si using cubic SiC as intermediate layers

We demonstrate suppression of crack generation in GaN epitaxy on Si using cubic SiC as intermediate layers. Crack-free GaN with a thickness of 2μm was obtained. Epilayers of SiC (0–1μm), thin AlN (50nm), and GaN (1–3μm) were prepared on 3in. (111)Si substrates (GaN∕AlN∕SiC∕Si) by metalorganic vapor-phase epitaxy. Cracking of GaN is suppressed with thicker SiC (1μm), whereas cracks are generated in GaN without SiC and with thinner SiC (50nm). Transmission electron microscopy analysis revealed monocrystalline wurzite structure of GaN. Current-voltage measurements showed breakdown voltage exceeding 250V, indicating its potential for high voltage application.

Stress reduction in epitaxial GaN films on Si using cubic SiC as intermediate layers

Stress in the epitaxial films of GaN on Si is reduced by using SiC as intermediate layers. The crystalline films of cubic SiC (0–1μm), thin AlN (50nm), and GaN (1–3μm) were prepared on 3in. (1 1 1) Si substrates—stacked in the order of GaN∕AlN∕SiC∕Si—by metalorganic vapor-phase epitaxy. It is revealed by Raman spectroscopy that the tensile stress in GaN is reduced to half (reduction of about 300MPa) for GaN on Si with SiC intermediate layers compared with GaN on Si without SiC intermediate layers. Because of stress reduction, crack-free GaN on Si with a thickness of 2μm was obtained by using SiC intermediate layers. Cracking was minimized even on thicker GaN on Si (3μm thick) with SiC intermediate layers. The SiC intermediate layers are promising for the realization of nitride based electronic devices on Si.

Electrical conduction and electronic structures of novel tetrathionaphthalene derivatives

The electrical conduction of pristine (undoped) and iodine doped vacuum deposited films of the novel donors, dibenzodithiotetra‐thionaphthalene and dibenzodithiotetraselenonaphthalene were measured. The electronic structures of these donor compounds were examined experimentally by ultraviolet photoelectron spectroscopy and theoretically by semiempirical MO calculations and compared with the corresponding data of tetrathiotetracene.