Seiro Miyoshi

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.

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 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

Intermediate range between N-doped GaP and GaP1-xNx alloys: difference in optical properties

Abstract Metalorganic vapor phase epitaxy (MOVPE) grown GaP 1- x N x metastable alloys with relatively dilute nitrogen concentrations (0.03% ≤ x ≤ 1.4%, i.e., 1 × 10 19 ≤[N]≤ 3 × 10 20 cm -3 ) have been studied with photoluminescence (PL). These nitrogen concentrations are especially interesting because they mediate between the N-doped GaP ([N] ≈ 10 19 cm -3 ), while the PL spectrum is represented by the emissions due to excitons bound to nitrogen atom pairs (NN i , i = 1, 2, 3,…), and the alloy, where the PL should be associated with the band gap. THe nitrogen concentration dependence of the PL spectra shows that the dominant emission changes from the shallow NN i centers (NN 4 , NN 5 ) to the deepest one (NN 1 ) with increasing x . The temperature dependence of the PL shows a similar systematic change in the spectrum. The integrated PL intensity versus x relationship indicates that at x > 0.4% (≃ 1 × 10 20 cm -3 ) nitrogen-doped GaP may be properly looked upon as a GaP 1- x N x alloy.

Surface orientation dependence of growth rate of cubic GaN

Abstract The metalorganic vapor phase epitaxy (MOVPE) growth of cubic GaN has been performed on the patterned GaAs(100) substrates which have (111)A or (111)B facets. It is found that the growth features are strongly dependent on the configuration of the pattern. It is deduced that these features come from the surface-orientation-dependent growth rate, which is in the order (111)B > (100) > (111)A, combined with the diffusion of Ga adatoms on the surface. Taking advantage of the growth on the patterned substrates, the diffusion length of the Ga adatoms on the GaAs(100) surface is estimated to be several microns in the typical case.

Formation of Cubic GaN on (111)B GaAs by Metal-Organic Vapor-Phase Epitaxy with Dimethylhydrazine

The microstructure of GaN grown on (111)B GaAs by a metal-orgnic vapor-phase epitaxy method has been examined by transmission electron microscopy. Trimethylgallium and dimethylhydrazine were used as the source materials. It was revealed that the GaN crystal has a zincblende structure and is formed heterogeneously penetrating into the GaAs substrate. In a GaN crystal, stacking faults propagate on {111} planes other than those normal to the growth direction.

Nitrogen concentration dependence of photoluminescence decay time in GaP1−xNx alloys

Abstract We report on the nitrogen concentration dependence of photoluminescence (PL) properties in GaP 1− x N x alloys. Time-resolved PL measurements reveal that the radiative transition and relaxation processes in GaP 1− x N x alloys with high nitrogen concentrations are significantly different from those with low concentrations where NN lines are clearly observed. The PL decay profile shows two distinct exponential processes with fast and slow decay times for high concentrations. With increasing N concentration, the fast decay component becomes dominant and the slow decay time becomes longer. The fast decay is attributed to the relaxation to nonradiative recombination centers. The slow decay indicates the long radiative lifetime due to the weak localization of excitons and the slow relaxation due to the scattered spatial distribution of the states. This is consistent with the fact that the PL occurs at the tails of the density of states.

Band Structure of GaP1-xNx(x=0.25, 0.5, 0.75) Ordered Alloys: Semiempirical Tight-Binding Calculation.

A semiempirical tight-binding calculation of the electronic structure of GaP1-xNx ordered alloys (x=0.25, 0.5, and 0.75) has been performed. The bowing parameter of the band gap is extremely large (7.6 and 3.2 eV for the \varGamma–X and the \varGamma–\varGamma transitions, respectively), which explains the experimental band gap reduction with increasing x when x<0.03 as observed by photoluminescence (PL) measurements [S. Miyoshi, H. Yaguchi, K. Onabe, R. Ito and Y. Shiraki: Appl. Phys. Lett. 63 (1993) 3506]. We have clarified that the large bowing originates from the large valence band (VB) offset between GaP and GaN (3.66 eV by Harrisons rule). The calculated band lineup of the GaP1-xNx alloy indicates that not only the GaP1-xNx–GaP heterojunction but also the GaP1-xNx–GaN heterojunction will show a type-II transition. The electronic structures of GaAs1-xPx and GaAs1-xSbx ordered alloys have also been calculated, and the values were consistent with the experimental band gap. The consistency confirms the validity of our calculation. The calculation is also applied to the electronic structure of a GaAs1-xNx ordered alloy (x=0.25, 0.5, and 0.75) which is also found to have large bowing parameters (4.0, 8.5, and 6.2 eV for the \varGamma–\varGamma, \varGamma–X, and \varGamma–L transitions, respectively) probably due to the large VB offset between GaAs and GaN.