Kentaro Onabe

MOVPE Growth of Cubic GaN on GaAs Using Dimethylhydrazine

Abstract High-quality cubic GaN epitaxial films have been successfully grown on (100) GaAs sunstrates by metalorganic vapor phase epitaxy (MOVPE) using 1,1-dimethylhydrazine (DMHy) as the nitrogen source material. The full width at half maximum (FWHM) of the X-ray diffraction profile of 0.65° has been obtained, which is the narrowest reported to date. The grown films were found to be made up of ridges with (111)B facets, with increasing film thickness. Raman peak characteristic of cubic symmetry has been obtained for the first time, showing that GaN films were of excellent quality.

Metalorganic vapor phase epitaxy of GaP1−xNx alloys on GaP

We demonstrate a successful growth of GaP1−xNx alloys on GaP by metalorganic vapor phase epitaxy (MOVPE). This alloy system is predicted to have an extremely large miscibility gap, ranging from x=0.0000003 to 0.9999997 at 700 °C. However, metastable alloys (x≤0.04) have been obtained at the growth temperature of 630–700 °C. We focused on the growth condition dependence of solid composition (x). The nitrogen incorporation increases with decreasing growth temperature. It also increases with increasing growth rate, possibly due to nonequilibrium circumstances in the MOVPE growth. Low‐temperature photoluminescence (PL) measurements show that the band gap of GaP1−xNx shifts to lower energy with increasing x.

Unstable Regions in III–V Quaternary Solid Solutions Composition Plane Calculated with Strictly Regular Solution Approximation

The behavior of unstable regions in the composition plane for III–V quaternary solid solutions made from among Al, Ga, In, P, As and Sb is analyzed, based on the strictly regular solution approximation for solid solutions. Temperature dependences of spinodal isotherms at 400–1000°C show that unstable regions cover a wide range of compositions. It is suggested that composition ranges exist where the spinodal temperature exceeds the melting point, so that such solid solutions can never be grown by near-equilibrium growth methods. Positions of quaternary critical points in the composition plane are also shown.

Transmission Electron Microscope Observation of Cubic GaN Grown by Metalorganic Vapor Phase Epitaxy with Dimethylhydrazine on (001) GaAs

Cross-sectional transmission electron microscope observation has been performed on the microstructure of GaN films grown on a (001) GaAs substrate by metalorgahic vapor phase epitaxy (MOVPE) using 1,1-dimethylhydrazine (DMHy) and trimethylgallium (TMG) as the sources of nitrogen and gallium, respectively. Before the deposition, the surface of the substrate was nitrided with DMHy. High-resolution images and electron diffraction patterns confirmed that the GaN films have a zincblende structure (β-GaN) with the lattice constant of a GaN=0.454 nm, and contain bands of stacking faults parallel to {111} planes. The interface between GaN and GaAs is made of {111} facets with no interlayer. Misfit dislocations are found to be inserted on the interface approximately every five atomic planes of GaAs. The nitridation treatment with only DMHy for 130 min is found to form a thick layer of β-GaN on the (001) GaAs substrate. Nuclei of β-GaN formed by the pretreatment of surface nitridation play an important role in growing GaN in a zincblende structure during the supply of DMHy and TMG. The formation of facets on the top surface of GaN and on the interface of GaN/GaAs is explained in terms of the diffusion of arsenic in β-GaN. The characteristics of the structure of GaN films grown at 600 and 650° C are also presented.

Photoluminescence properties of cubic GaN grown on GaAs(100) substrates by metalorganic vapor phase epitaxy

Photoluminescence (PL) measurements were performed on cubic GaN films grown on GaAs(100) substrates by metalorganic vapor phase epitaxy. The cubic GaN films show a high optical quality that enables us to study the PL spectra in detail. From temperature and excitation intensity dependence, the emission lines at 3.274 and at 3.178 eV were assigned to the excitonic transition and the donor–acceptor pair transition, respectively. We also observed two additional emission lines at 3.088 and 3.056 eV. An excitonic emission at 3.216 eV with full width half maximum value as small as 73 meV was observed at 300 K.

Naturally formed ZnCdSe quantum dots on ZnSe (110) surfaces

We successfully realized ZnCdSe quantum dots on a cleavage-induced ZnSe (110) surface by depositing a ZnSe/ZnCdSe/ZnSe heterostructure under growth conditions that cannot lead to layer-by-layer growth of ZnSe. This growth mode introduces surface roughness to the newly deposited ZnSe layer, and ZnCdSe quantum dots are then formed. Cathodoluminescence and microphotoluminescence measurements demonstrate the formation of quantum dots.

Crystal Structure of GaN Grown on 3C-SiC Substrates by Metalorganic Vapor Phase Epitaxy

GaN films were grown on 3C-SiC substrates by metalorganic vapor phase epitaxy (MOVPE) using 1,1-dimethylhydrazine (DMHy) as the N source. The crystal structure was strongly affected by both the growth temperature and the V/III ratio. At 600° C, only hexagonal GaN films with their c-axis perpendicular to the substrate surface were grown. At 800° C, relatively high V/III ratios resulted in the growth of hexagonal GaN with their c-axis oriented in the [111] direction while cubic GaN films were obtained at lower V/III ratios. The origin of [111]-oriented hexagonal GaN is also discussed.

Photoluminescence excitation spectroscopy of GaP1−xNx alloys: conduction-band-edge formation by nitrogen incorporation

We have investigated the conduction-band-edge formation in GaP 1-x N x alloys by nitrogen incorporation into GaP using photoluminescence excitation (PLE) spectroscopy. The PLE spectra of GaP 1-x N x alloys with various nitrogen concentrations show that the absorption edge shifts to lower energies with increasing nitrogen concentration. From the nitrogen concentration dependence of the absorption edge energy we found that the conduction-band-edge formation in Ga 1-x N x alloys originates from the formation of the A line.

Selective Growth of Cubic GaN in Small Areas on Patterned GaAs(100) Substrates by Metalorganic Vapor Phase Epitaxy

The metalorganic vapor phase epitaxy growth of cubic CaN in small areas on SiO 2 -patterned CaAs substrates has been performed. We have succeeded in selective growth without deposition on the SiO 2 mask at temperatures between 620 and 675 o C. The crystal quality of cubic CaN has been improved through growth in small areas on patterned CaAs substrates. It is found that the grain size becomes larger and the full width at half maximum of the X-ray diffraction peak of cubic CaN becomes narrower on patterned substrates than on unpatterned ones

Metalorganic Vapor Phase Epitaxy Growth of High Quality Cubic GaN on GaAs (100) Substrates

We report on the growth of high quality cubic GaN films on GaAs (100) substrates by low pressure metalorganic vapor phase epitaxy. The GaN films exhibit a smooth surface which is free from cracks. X-ray diffraction shows the cubic nature of the GaN films. X-ray rocking curve with ω scan shows that the crystal quality of GaN films improves markedly with increasing growth temperatures. Photoluminescence measurements confirm the high quality of the cubic GaN films. The full width at half maximum of excitonic emission from the cubic GaN films is as narrow as 70 meV at 300 K.