Papers by Keyword: MOVPE

Abstract: To fabricate low threshold semiconductor lasers on silicon, strained quantum well structure is introduced to the well layer. The crystalline, optical, and laser characteristics of GaInAsP separate confinement heterostructure with multiple quantum wells (SCH-MQW) are investigated under various percentages of strain applied to the active layer. It is found that the strain-based III-V heterostructures possessed good crystalline and optical properties to study the current-light characteristics of the lasers. One of the successful achievements is that we do the laser growth only after fabricating InP thin film bonded to silicon substrate using hydrophilic bonding mechanism. GaInAsP SCH-MQW laser structures were fabricated on the directly bonded InP/Si substrate using metal-organic vapor phase epitaxy (MOVPE). Through our integration process and the intentional introduction of strain into the active layer, a significant reduction in threshold current was successfully achieved on the InP/Si substrate. Furthermore, a comparative analysis of the strain distribution within the quantum well structures between the InP and InP/Si substrates was conducted to better understand its impact on device performance.

Abstract: InGaAsN on Ge (001) is proposed to be a part of the InGaP(N)/InGaAs/InGaAsN/Ge four-junction solar cell to increase a conversion efficiency over 40%. In this work, InGaAsN lattice-matched film and GaAs buffer layer grown on Ge (001) substrate by metal organic vapor phase epitaxy (MOVPE) were examined by transmission electron microscopy (TEM). Electron diffraction pattern of InGaAsN taken along the [110]-zone axis illustrates single diffracted spots, which represent a layer with a uniformity of alloy composition. Cross-sectional bright field TEM image showed line contrasts generated at the GaAs/Ge interface and propagated to the InGaAsN layer. Dark field TEM images of the same area showed the presence of boundary-like planar defects lying parallel to the growth direction in the InGaAsN film and GaAs buffer layer but not in the Ge substrate. TEM images with the (002) and (00-2) reflections and the four visible {111} planes reflections illustrated planar defects which are expected to attribute to antiphase boundaries (APBs). Moreover, the results observed from atomic force microscopy (AFM) and field emission electron microscopy (FE-SEM) demonstrated the surface morphology of InGaAsN film with submicron-sized domains, which is a characteristic of the APBs.

Abstract: The author introduces and summarizes the results on bottom-up formation and structural characterizations obtained so far for the MnAs nanoclusters and MnAs/semiconductor nanowire hybrids. First, MnAs nanoclusters were grown by selective-area metal-organic vapor phase epitaxy. They had a hexagonal NiAs-type crystal structure. Their <00(0)1> direction was parallel to <111>B direction of zinc-blende-type GaAs substrates. Hybrid MnAs/GaAs nanowires, subsequently, were fabricated by combining selective-area metal-organic vapor phase epitaxy of GaAs nanowire templates and endotaxial MnAs nanoclustering on them. MnAs nanoclusters ordered at six ridges of hexagonal GaAs nanowires were formed possibly owing to more atomic steps between {0-11} crystal facets. In the case of hybrid MnA/InAs nanowires, MnAs nanoclusters were not formed only on the {0-11} side-walls, and/or ridges between them, but on the top {111}B crystal facets of hexagonal InAs nanowires. MnAs nanoclusters were formed much deeper into the InAs nanowires than into the GaAs nanowires. These facts are possibly due to the InAs nanowires are thermally less stable than the GaAs nanowires. Some of the hybrid MnA/InAs nanowires were bent at the parts where the MnAs nanoclusters were grown into the host nanowires mainly owing to the strain effects.

Abstract: We have investigated an effect of N incorporation on InGaAsN on Ge (001), which is proposed to be a part of the InGaP(N)/InGaAs/InGaAsN/Ge four-junction solar cell, and on its growth behavior. Results obtained from high resolution X-ray diffraction and Raman scattering demonstrated that high quality In_0.11Ga_0.89As_1-yN_y films with N (y) contents up to 5% were successfully grown on n-type doped Ge (001) substrate by metalorganic vapor phase epitaxy using low-temperature (500°C) GaAs buffer layer. As expectation, the In_0.11Ga_0.89As_0.96N_0.04 film is examined to be under lattice-matching condition. Anti-phase domains were observed for the film without N incorporation, which exhibits submicron-size domains oriented along the [110] direction on the grown surface. With increasing N content, the domains become less orientation, and present in a larger domain size. Based on results of transmission electron microscopy, a high density of anti-phase domains was clearly observed at the interface of low-temperature GaAs buffer layer and Ge substrate. On the other hand, it is found to drastically reduce within the N-contained InGaAsN region. Furthermore, the lattice-matched In_0.11Ga_0.89As_0.96N_0.04 film is well developed to reduce the density of anti-phase domains.

Abstract: Epitaxial lateral overgrowth (ELO) was performed to grow cubic GaN layers on stripe-patterned GaAs (001) substrates via metalorganic vapor phase epitaxy. Growth time was varied from 10 to 120 minutes to investigate an evolution of growth morphologies and crystal structures of GaN, which were respectively analyzed by scanning electron microscopy and micro-Raman scattering spectroscopy. Growth features of ELO cubic GaN for [1-10] oriented mask stripe-pattern showed the {113} side-wall facets. On the other hand, the {111} side-wall facets were observed for ELO cubic GaN grown on the [110] oriented mask stripe-pattern. In case of [100] oriented mask stripe-pattern, growth feature with top rough surface and unclear side-wall facets was obtained. Micro-Raman spectroscopy was used as a tool to identify both cubic and hexagonal GaN structures performed on surface of the top and side-wall facets of the GaN stripes. ELO cubic GaN layer with growth time of 60 min along the [1-10] oriented mask stripe-pattern exhibited the highest ratio of cubic to hexagonal GaN, which was examined from an integrated intensity of LO phonon mode at 738 cm^-1 for cubic GaN comparing with that of hexagonal GaN, appearing at A₁ (TO) 538 cm^-1, E₁ (TO) 558 cm^-1 and E₂ (high) 568 cm^-1.

Abstract: It is imperative to determine the dependence of the quality and characteristics of the epitaxial film on different growth parameters. A mathematical model has been developed showing the effect of different growth parameters e.g. temperature, TMI and TEG flow rate, molar ratio on epitaxial film. This model is considered for InGaN film on GaN template with an Indium mole fraction up to 0.4 by Metal Organic Vapor Phase Epitaxy (MOVPE). The results obtained from this model has been compared and fitted with experimentally obtained data through XRD, RSM, PL, SEM etc. Finally, a phase diagram has been proposed to interpret the phase separation and Indium content evolution under the influence of growth temperature and precursor gas flow.

Abstract: We have studied the properties of photoluminescence (PL) from individual isoelectronic traps formed by nitrogen-nitrogen (NN) pairs in nitrogen atomic-layer doped (ALD) GaAs. Micro-PL measurements were performed to investigate the properties of single photons generated from individual isoelectronic traps. Twin PL peaks were observed from individual isoelectronic traps in nitrogen ALD GaAs (001). The PL transitions at longer and shorter wavelength sides were linearly polarized in the [110] and [1-10] directions, respectively. The peak splitting and polarization properties can be explained by some in-plane anisotropy most likely due to strain in host crystal. From individual isoelectronic traps in nitrogen ALD GaAs (111), a single PL peak with random polarization was observed, showing that the growth on (111) surface is an effective way to obtain unpolarized single photons. As for nitrogen ALD GaAs (110), different polarization properties were obtained depending on the atomic configuration of NN pairs. In addition, we have used AlGaAs layers to diminish the in-plane anisotropy and could successfully obtained single emission lines with unpolarized character. Introducing AlGaAs layers was also useful for improving the luminescence efficiency.

Abstract: We fabricated a thin film Peltier device based on an InSb film and a SbTe film. N-type InSb thin films were grown on sapphire (0001) substrate with InAsSb buffer layer by metalorganic vapor phase epitaxy, and P-type SbTe thin films were deposited on the substrate by electron beam evaporation. N-type and P-type films were separated on the substrate, and between them, a Au thin film was deposited by direct-current sputtering. We observed partial Peltier effect in the device.

Abstract: The GaAs1-xNx alloy semiconductor has been grown on GaAs (001), (111)A and (011) substrates by metalorganic vapor-phase epitaxy. High resolution X-ray diffraction and Raman scattering were employed to examine the effective N content and the growth rate, as a function of the substrate-surface orientation. The growth rate, which was assessed though the clear Pendellösung fringes, and the N content were found to change dramatically with the substrate-surface orientations. The N content was determined in the order (111)A > (001) > (011). While, the growth rate is in the order, (001) > (011) > (111)A. The effect of substrate-surface orientation on the N incorporation found in the present study is interpreted in terms of the difference in the growth rate on each surface orientation and the number of dangling bonds with which the N atoms can be trapped on the growing surface. Our results show that controlled nitrogen incorporating for GaAsN is successfully achieved and can be applied to the fabrication of some novel structures such as a spontaneous N content modulated structure, which is applicable to high performance long wavelength laser diodes.

Abstract: The fundamental growth issues of AlN and AlGaN on sapphire and SiC using metalorganic vapor phase epitaxy, particularly the growth of AlN and AlGaN on a groove-patterned template are reviewed. In addition, the conductivity control of AlGaN is shown. The conductivity control of p-type AlGaN, particularly the realization of a high hole concentration, is essential for realizing high-efficiency UV and DUV LEDs and LDs.