Room-temperature optical transitions in Mg-doped cubic GaN/GaAs(100) grown by metalorganic chemical vapor deposition

The mechanism of room-temperature optical transitions in a Mg-doped cubic GaN epilayer grown on GaAs(100) by metalorganic chemical vapor deposition has been investigated. By examining the dependence of photoluminescence on the excitation intensity (which varied over four orders) at room temperature, four different emissions with different origins were identified. A blue emission at similar to 3.037 eV was associated with a shallow Mg acceptor, while three different lower-energy emissions at similar to 2.895, similar to 2.716, and similar to 2.639 eV were associated with a deep Mg complex. In addition to a shallow acceptor at E congruent to 0.213 eV, three Mg-related deep defect levels were also found at around 215, 374, and 570 meV (from the conduction band). (C) 2000 American Institute of Physics. [S0021-8979(00)01904-6].

Gallium diffusion through cubic GaN films grown on GaAs(100) at high-temperature using low-pressure MOVPE

Cubic GaN films were grown on GaAs(1 0 0) substrates by low-pressure metalorganic vapor-phase epitaxy at high temperature. We have found a nonlinear relation between GaN film thickness and growth timer and this nonlinearity becomes more obvious with increasing growth temperature. We assumed it was because of Ga diffusion through the GaN film, and developed a model which agrees well with the experimental results. These results raise questions concerning the role of Ga diffusion through the GaN film, which may affect the electrical and optical properties of the material. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Effects of growth temperature on highly mismatched InAs grown on GaAs substrates by MBE

InAs layers were grown on GaAs by molecular beam epitaxy (MBE) at substrate temperature 450 and 480 degrees C, and the surface morphology was studied with scanning electron microscopy (SEM). We have observed a high density of hexagonal deep pits for samples grown at 450 degrees C, however, the samples grown at 480 degrees C have smooth surface. The difference of morphology can be explained by different migration of cations which is temperature dependent. Cross-sectional transmission electron microscopy (XTEM) studies showed that the growth temperature also affect the distributions of threading dislocations in InAs layers because the motion of dislocations is kinetically limited at lower temperature. (C) 1998 Elsevier Science B.V. All rights reserved.

High Characteristic Temperature 1.3 mu m InAs/GaAs Quantum-Dot Lasers Grown by Molecular Beam Epitaxy

We report the molecular beam epitaxy growth of 1.3 mu m InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T-0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 mu m and a cavity length of 1200 mu m are fabricated and tested in the pulsed regime under different temperatures. It is found that T-0 of the QD lasers is as high as 532K in the temperature range from 10 degrees C to 60 degrees C. In addition, the aging test for the lasers under continuous wave operation at 100 degrees C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.

Substrate temperature dependence of ZnTe epilayers grown on GaAs(001) by molecular beam epitaxy

ZnTe thin films have been grown on GaAs(0 0 1) substrates at different temperatures with constant Zn and Te beam equivalent pressures (BEPs) by molecular beam epitaxy (MBE). In situ reflection high-energy electron diffraction (RHEED) observation indicates that two-dimensional (2D) growth mode can be established after around one-minute three-dimensional (3D) nucleation by increasing the substrate temperature to 340 degrees C. We found that Zn desorption from the ZnTe surface is much greater than that of Te at higher temperatures, and estimated the Zn sticking coefficient by the evolution of growth rate. The Zn sticking coefficient decreases from 0.93 to 0.58 as the temperature is elevated from 320 to 400 degrees C. The ZnTe epilayer grown at 360 degrees C displays the narrowest full-width at half-maximum (FWHM) of 660 arcsec from (0 0 4) reflection in double-crystal X-ray rocking curve (DCXRC) measurements. The surface morphology of ZnTe epilayers is strongly dependent on the substrate temperature, and the root-mean-square (RMS) roughness diminishes drastically with the increase in temperature.

High resistance AlGaAs/GaAs quantum cascade detectors grown by solid source molecular beam epitaxy operating above liquid nitrogen temperature

This work was supported by the National Research Projects of China (grant numbers are 60525406, 60736031, 60806018, 60906026, 2006CB604903, 2007AA03Z446 and 2009AA03Z403, 10990100, respectively). The authors would like to thank P Liang, Y Hu, H Sun, X L Zhang, B J Sun, H L Zhen and N Li for their help in processing and characterization.

Twinning in Low-Temperature MOCVD Grown GaN on (001) GaAs Substrate

GaN buffer layers (thickness ～60nm) grown on GaAs(001) by low-temperature MOCVD are investigated by X-ray diffraction pole figure measurements using synchrotron radiation in order to understand the heteroepitaxial growth features of GaN on GaAs(001) substrates. In addition to the epitaxially aligned crystallites,their corresponding twins of the first and the second order are found in the X-ray diffraction pole figures. Moreover, { 111 } q scans with χ at 55° reveal the abnormal distribution of Bragg diffractions. The extra intensity maxima in the pole fig ures shows that the process of twinning plays a dominating role during the growth process. It is suggested that the polarity of { 111 } facets emerged on (001) surface will affect the growth-twin nucleation at the initial stages of GaN growth on GaAs(001) substrates. It is proposed that twinning is prone to occurring on { 111 } B, N-terminated facets.

Room-temperature continuous-wave lasing from InAs GaAs quantum dot laser grown by molecular beam epitaxy

Quantum dot lasers are predicted to have proved lasing characteristics compared to quantum well and quantum wire lasers. We report on quantum dot lasers with active media of vertically stacked InAs quantum dots layers grown by molecular beam epitaxy. The laser diodes were fabricated and the threshold current density of 220 A/cm(2) was achieved at room temperature with lasing wavelength of 951 nm. The characteristic temperature To was measured to be 333K and 157K for the temperature range of 40-180K and 180-300K, respectively.

Room-temperature continuous-wave operation of GaInNAs/GaAs quantum dot laser with GaAsN barrier grown by solid source molecular beam epitaxy

We present the results of GaInNAs/GaAs quantum dot structures with GaAsN barrier layers grown by solid source molecular beam epitaxy. Extension of the emission wavelength of GaInNAs quantum dots by ~170nm was observed in samples with GaAsN barriers in place of GaAs. However, optimization of the GaAsN barrier layer thickness is necessary to avoid degradation in luminescence intensity and structural property of the GaInNAs dots. Lasers with GaInNAs quantum dots as active layer were fabricated and room-temperature continuous-wave lasing was observed for the first time. Lasing occurs via the ground state at ~1.2μm, with threshold current density of 2.1kA/cm[superscript 2] and maximum output power of 16mW. These results are significantly better than previously reported values for this quantum-dot system.

Effect of temperature on the optical properties of GaAsSbN/GaAs single quantum wells grown by molecular-beam epitaxy

GaAsSbN/GaAs strained-layer single quantum wells grown on a GaAs substrate by molecular-beam epitaxy with different N concentrations were studied using the photoluminescence (PL) technique in the temperature range from 9 to 296 K. A strong redshift in optical transition energies induced by a small increase in N concentration has been observed in the PL spectra. This effect can be explained by the interaction between a narrow resonant band formed by the N-localized states and the conduction band of the host semiconductor. Excitonic transitions in the quantum wells show a successive red/blue/redshift with increasing temperature in the 2-100 K range. The activation energies of nonradiative channels responsible for a strong thermal quenching are deduced from an Arrhenius plot of the integrated PL intensity. (C) 2003 American Institute of Physics.

Influence of magnetic clusters on electrical and magnetic properties of In1-xMnxSb/GaAs dilute magnetic semiconductor grown by liquid phase epitaxy

In1-xMnxSb films have been grown with different Mn doping concentrations (x = 0.0085, 0.018, 0.029 and 0.04) beyond the equilibrium 14 solubility limit by liquid phase epitaxy. We have studied temperature dependent resistivity, the Hall effect, magnetoresistance and magnetization for all compositions. Saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic clusters in the film which has been verified by scanning electron microscopy studies. The anomalous Hall coefficient is found to be negative. Remnant field present on the surface of the clusters seems to affect the anomalous Hall effect at very low fields (below 350 Gauss). In the zero field resistivity, a variable-range hopping conduction mechanism dominates below 3.5 K for all samples above which activated behavior is predominant. The temperature dependence of the magnetization measurement shows a magnetic ordering below 10 K which is consistent with electrical measurements. (c) 2007 Elsevier Ltd. All rights reserved.

Structural and optical characterization of vertical GaAs/GaP core-shell nanowires grown on Si substrates

GaAs nanowires were grown on Si (111) substrates. By coating a thin GaAs buffer layer on Si surface and using a two-temperature growth, the morphology and crystal structure of GaAs nanowires were dramatically improved. The strained GaAs/GaP core-shell nanowires, based on the improved GaAs nanowires with a shell thickness of 25 nm, showed a significant shift in emission energy of 260 meV from the unstrained GaAs nanowires. © 2010 IEEE.

Improvement of morphology, structure, and optical properties of GaAs nanowires grown on Si substrates

We investigate vertical and defect-free growth of GaAs nanowires on Si (111) substrates via a vapor-liquid-solid (VLS) growth mechanism with Au catalysts by metal-organic chemical vapor deposition (MOCVD). By using annealed thin GaAs buffer layers on the surface of Si substrates, most nanowires are grown on the substrates straight, following (111) direction; by using two temperature growth, the nanowires were grown free from structural defects, such as twin defects and stacking faults. Systematic experiments about buffer layers indicate that V/III ratio of precursor and growth temperature can affect the morphology and quality of the buffer layers. Especially, heterostructural buffer layers grown with different V/III ratios and temperatures and in-situ post-annealing step are very helpful to grow well arranged, vertical GaAs nanowires on Si substrates. The initial nanowires having some structural defects can be defect-free by two-temperature growth mode with improved optical property, which shows us positive possibility for optoelectronic device application. ©2010 IEEE.

Metamorphic InGaAs p-i-n Photodetectors with 1.75 mu m Cut-Off Wavelength Grown on GaAs

Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 mu m at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 x 10(-6) A/cm(2) at 0 V bias and 2.24 x 10(-4) A/cm(2) at a reverse bias of 5 V. At a wavelength of 1.55 mu m, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 mu m diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence (PL) and lasing properties of InAs/GaAs quantum dots (QDs) with direrent growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the lowgrowth rate sample shows a greater blue shift of PL peak wave length. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blue shift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.