Toshiki Hikosaka

Optical and electrical properties of (1-101)GaN grown on a 7° off-axis (001)Si substrate

Uniform growth of (1-101)GaN was performed on coalesced stripes of GaN which had been prepared by selective metalorganic vapor phase epitaxy on a 7° off-axis (001)Si substrate via an AlN intermediate layer. The cathodoluminescence spectra at 4 K exhibited a donor bound excitonic emission at 358 nm followed by defect-related emission peaks at 363, 371, and 376 nm. The 363 and 376 emission bands are observed upon the coalescence region. The Hall measurements exhibited p-type conduction at 80–300 K (the hole carrier density 6.3×1012 cm−2 and hole mobility 278 cm2/V s at 100 K). The activation energy of the acceptor was estimated to be 60 meV. The possible origin of the p-type conduction is discussed in relation to the unintentionally doped carbon.

Al doping in (1−101)GaN films grown on patterned (001)Si substrate

The effect of Al doping on crystalline and optical properties of semipolar (1−101)GaN was investigated. The samples were grown on a patterned (001)Si substrate by selective metal-organic vapor phase epitaxy. The x-ray analyses showed that the strain in the (1−101)GaN layer is reduced substantially by the Al doping. Moreover, the cathode-luminescence (CL) intensity of the band edge emission band was enhanced and the linewidth became narrow. The CL images showed the reduction of dislocation density. These results show that the small amount of Al atoms in GaN improves the crystalline and optical properties. The results are attributed to the dislocation pinning and solution hardening effect due to Al atoms.

Nature of yellow luminescence band in GaN grown on Si substrate

High-optical-quality GaN was grown on a (111)Si substrate by metal–organic vapor phase epitaxy using an AlInN buffer layer and an indium doped AlN nucleation layer. The photoluminescence spectra at room temperature showed a strong and narrow edge-emission peak and weak defect-related emission bands. We found four spectral peaks in the green and yellow luminescence bands at G0: 514.5 nm (2.410 eV), G1: 546.5 nm (2.269 eV), Y1: 553.5 nm (2.240 eV), and Y0: 584.5 nm (2.121 eV), independent of the growth methods/conditions. The results suggest that the emission is associated with an intrinsic defect such as a Ga vacancy.

Carbon Incorporation on (1101) Facet of AlGaN in Metal Organic Vapor Phase Epitaxy

Using C2H2 as the source material, the incorporation of carbon into a (1101)AlGaN facet was studied in metal organic vapor phase epitaxy. The cathodo luminescence (CL) spectra for the sample surface were dominated by two near-band-edge emission peaks, assigned as a donor bound exciton (DBE) peak and a carbon-related exciton peak. The emission intensity of the carbon related exciton peak was enhanced by carbon doping, and the enhancement was more efficient on the (1101) facets than on the (0001) facet. It was found that more carbon is incorporated in a sample with high Al composition on the (1101) facets. In the case of Mg doping, on the other hand, the optical properties on the (1101) facets are nearly the same as those of the (0001) facet.

Selective growth and impurity incorporation in semipolar GaN grown on Si substrate

Semipolar nitrogen terminated (1-101)GaN film was grown on a patterned (001)Si substrate using selective area metal organic vapor phase epitaxy. By using a high temperature grown AlN buffer layer upon oblique (111) Si facets on the substrate, we achieved a GaN crystal film with low dislocation density. Because the growth of GaN crystal was selforganized on the facets, we achieved two dimensional growth mode automatically, and the surface roughness was as small as 0.2nm. Incorporation of magnesium (Mg) and carbon (C) in the (1-101) GaN was studied extensively. It was found that the Mg doping efficiency is superior on (1-101) face to that on (0001) face. In case of C doping, a shallow acceptor level was generated in (1-101) face and p-type conduction was realized.

Acceptor Level due to Carbon in a (1–101)AlGaN

Carbon doping into N terminated GaN and AlGaN epitaxial layer is investigated. We found strong carbon related emission band which is insensitive to the annealing effect. The results suggested a shallow acceptor level which was slightly increased by the increase of the Al composition. A possible mechanism of the shallow level is discussed.