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High lateral density quantum dot (QD) structures are self-formed by growing GaAs/InAs short-period superlattices (SLs) on InP (411)A substrates by gas source molecular beam epitaxy. Multilayer QD structures sandwiched with InP barrier layers showed a strong photoluminescence emission. The 1.3–1.6 μm wavelength emission was easily obtained and precisely controlled by regulating the SL period as well as the number of InAs monolayers (layer thickness). This wavelength control can be understood by considering the carrier confinement along the growth direction as well as the effective well depth change. [ABSTRACT FROM AUTHOR]

GaN nanorod films have been grown on Si(001) substrates with native silicon oxides by radio-frequency plasma-enhanced molecular beam epitaxy. GaN nanorod films are made up of single-crystalline nanorods with a so-called (0001) fiber-like texture. Each nanorod is elongated along c axis in perpendicular to the substrate surface and has no preferential axis in film plane. Excellent electron field emission characteristics were observed for the fabricated GaN nanorod films with a field emission threshold as low as 1.25 V/μm at a current density of 0.1 μA/cm2 and a field emission current density as high as 2.5 mA/cm2 at an applied field of 2.5 V/μm. These excellent characteristics are attributed to the geometrical configuration of nanorods and their good crystalline quality as well as the low electron affinity of GaN. [ABSTRACT FROM AUTHOR]

TlInGaAs quaternary alloy layers were grown on InP substrates by gas-source molecular-beam epitaxy. Refractive index dispersions were determined at the temperature range of 300–340 K in the photon-energy region below and a little above the direct bandedge E0 by the optical reflectance measurements. The temperature dependence of the refractive index was analyzed with the first-order Sellmeier equation. The temperature dependence of the E0 edge was also determined by the absorption measurements. It was found that the temperature coefficients of both refractive index and E0 edge of TlInGaAs are much smaller than those for InGaAs. These results facilitate the fabrication of the temperature-stable-wavelength optoelectronic devices using this alloy system. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the influence of hydrogen on the step flow growth of gallium arsenide (GaAs) on the vicinal surfaces by gas-source migration enhanced epitaxy. Analysis of the reflection high-energy electron diffraction intensity oscillation; Advantage of using AsH[sub 3] over solid As; Factors responsible for the enhancement of step flow growth of GaAs.

Abstract: Cubic GaCrN layers are grown on MgO(001) substrates at 350–700°C by plasma-assisted molecular beam epitaxy. Substrate temperature dependences of their structural and magnetic properties were systematically studied. It is found that the solubility limit of Cr atoms in cubic GaCrN is dramatically improved by the low temperature (350°C) growth, though crystalline quality becomes poorer. It is also observed that the magnetic ordering increases with Cr content in the low Cr content region, but after showing highest ordering it decreases in the high Cr content region. The Cr content range showing ferromagnetic behavior increases with lowering substrate temperature. However, the magnetization vs. magnetic field curve shows “emaciated” hysteresis for the low temperature grown samples. [Copyright &y& Elsevier]

Abstract: Epitaxial growth of transition-metal Cr-doped cubic-phase GaN (GaCrN) layers on GaAs (001) substrates by plasma-assisted molecular-beam epitaxy and the observation of ferromagnetism above room temperature are reported for the first time. Influence of V/III ratio and Cr-cell temperature on the physical properties of the grown layers is studied extensively. X-ray diffraction studies and transmission electron microscopy observations confirm the predominantly cubic-nature of GaN and GaCrN for the epitaxial layers grown under Ga-rich condition. Cr dopant atoms exhibit surfactant nature and improve the crystalline quality and also enhance the growth of cubic-phase of GaN and GaCrN. Strong and broad blue-luminescent band (centered at 2.85eV) is induced by the Cr doping in GaN. The saturation magnetization of the grown layers initially increases with Cr concentration and then decreases for further increase of Cr concentration. [Copyright &y& Elsevier]

Abstract: Structural and magnetic properties of cubic GaCrN (c-GaCrN) grown on MgO (001) substrate by plasma-assisted molecular beam epitaxy (PAMBE) were studied with X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) analysis and a superconducting quantum interference device (SQUID) magnetometer. The Cr concentration dependence of XRD rocking curve showed that high Cr-doping induced mosaic block effect in the c-GaCrN layer. It was found that the saturation magnetization (M s) and the coercive field (H c) obtained from the M–H curves decrease with increase in the Cr concentration. XAFS results showed that the ratios of Cr atoms substituted for Ga sites to Cr atoms incorporated in low Cr-doped samples (Cr∼0.2%) are higher than those in highly Cr-doped samples (Cr∼3%), and that the other Cr atoms are segregated to form a CrN phase with NaCl structure. This XAFS results correspond to the SQUID data that the amounts of magnetically active Cr atoms in c-GaCrN decrease for the highly Cr-doped samples. X-ray absorption near-edge structure spectra also supports these results. [Copyright &y& Elsevier]

Abstract: We have grown polycrystalline GaN on quartz, refractory metal (W, Mo, Ta and Nb) and Si substrates by using plasma-assisted molecular beam epitaxy. It has been found that polycrystalline GaN grown on quartz and refractory metal substrates shows a strong band-edge emission without yellow emission. GaN growth on Si with native oxide produces well c-orientated nanorods exhibiting a low field emission threshold and high emission current density. We will review the growth of polycrystalline GaN films and the evaluation of their optical properties and electron field emission characteristics. [Copyright &y& Elsevier]

Abstract: GaCrN-based ferromagnet/nonmagnet/ferromagnet trilayer structures were grown by radio frequency molecular beam epitaxy. During GaN and GaCrN growth, reflection high-energy electron diffraction pattern showed thin streaks and Kikuchi lines, indicating surface flatness and high crystalline quality. Clear hysteresis and saturation characteristics were observed in the magnetization versus magnetic field curves at all the measuring temperatures. The coercivity H c was about 130Oe at 10K. Step-like hysteresis loops were also observed at 10 and 300K because of different Cr concentrations in the two GaCrN layers. Photoluminescence emission was observed from GaCrN. Hysteresis loop was observed in the magnetic field dependence of vertical electrical resistance. [Copyright &y& Elsevier]

To realize the temperature-stable threshold-current and lasing-wavelength 1.3–1.5 μm laser diodes, TlInGaAsN/AlGaAs heterostructures were proposed. As a first step, TlInGaAs was successfully grown, for the first time, on GaAs substrate by molecular beam epitaxy. The incorporation of Tl was confirmed with reflection high-energy electron diffraction intensity oscillation measurement. Photoluminescence (PL) measurements were conducted on the TlInGaAs/GaAs and InGaAs/GaAs heterostructure samples and the red shift of the PL peak energy was observed for the TlInGaAs/GaAs samples, as expected. [Copyright &y& Elsevier]