The refractive nonlinearities of InAs/GaAs quantum dots above-bandgap energy

The third-order optical nonlinear refractive properties of InAs/GaAs quantum dots grown by molecular beam epitaxy have been measured using the reflection Z-scan technique at above-bandgap energy. The nonlinear refractive index and nonlinear absorption index of the InAs/GaAs quantum dots were determined for wavelengths from 740 to 777 nm. The measured results are compared with the nonlinear refractive response of several typical III-V group semiconductor materials. The corresponding mechanisms responsible for the large nonlinear response are discussed.

First-principles study of p-type transparent conductive oxides CuXO2 (X=Y, Sc, and Al)

Using first-principles methods we have calculated electronic structures, optical properties, and hole conductivities of CuXO2 (X=Y, Sc, and Al). We show that the direct optical band gaps of CuYO2 and CuScO2 are approximately equal to their fundamental band gaps and the conduction bands of them are localized. The direct optical band gaps of CuXO2 (X=Y, Sc, and Al) are 3.3, 3.6, and 3.2 eV, respectively, which are consistent with experimental values of 3.5, 3.7, and 3.5 eV. We find that the hole mobility along long lattice c is higher than that along other directions through calculating effective masses of the three oxides. By analyzing band offset we find that CuScO2 has the highest valence band maximum (VBM) among CuXO2 (X=Y, Sc, and Al). In addition, the approximate transitivity of band offset suggests that CuScO2 has a higher VBM than CuGaO2 and CuInO2 [Phys. Rev. Lett. 88, 066405 (2002)]. We conclude that CuScO2 has a higher p-type doping ability in terms of the doping limit rule. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2991157]

Blue-green optically pumped GaN-based vertical cavity surface emitting laser

Blue-green GaN-based vertical cavity surface emitting lasers (VCSELs) were fabricated with two dielectric Ta2O5/SiO2 distributed Bragg reflectors. Lasing action was observed at a wavelength of 498.8 nm at room temperature under optical pumping. Threshold energy density and emission linewidth were 189 mJ/cm(2) and 0.15 nm, respectively. The result demonstrates that blue-green VCSELs can be realised using III-nitride semiconductors.

Photoluminescence study of AlGaInP/GaInP quantum well intermixing induced by zinc impurity diffusion

AlGaInP/GaInP quantum well intermixing phenomena induced by Zn impurity diffusion at 540 degrees C were studied using room-temperature photo luminescence (PL) spectroscopy. As the diffusion time increased from 40 to 120 min, PL blue shift taken on the AlGaInP/GaInP quantum well regions increased from 36.3 to 171.6 meV. Moreover, when the diffusion time was equal to or above 60 min, it was observed firstly that a PL red shift occurred with a PL blue shift on the samples. After detailed analysis, it was found that the red-shift PL spectra were measured on the Ga0.51In0.49P buffer layer of the samples, and the mechanism of the PL red shift and the PL blue shift were studied qualitatively. (C) 2007 Elsevier B.V. All rights reserved.

Magnetization of two-dimensional heavy holes with boundaries in a perpendicular magnetic field

The magnetisation of heavy holes in III-V semiconductor quantum wells with Rashba spin-orbit coupling (SOC) in an external perpendicular magnetic field is studied theoretically. We concentrate on the effects on the magnetisation induced by the system boundary, the Rashba SOC and the temperature. It is found that the sawtooth-like de Haas-van Alphen (dHvA) oscillations of the magnetisation will change dramatically in the presence of such three factors. Especially, the effects of the edge states and Rashba SOC on the magnetisation are more evident when the magnetic field is smaller. The oscillation center will shift when the boundary effect is considered and the Rashba SOC will bring beating patterns to the dHvA oscillations. These effects on the dHvA oscillations are preferably observed at low temperatures. With increasing temperature, the dHvA oscillations turn to be blurred and eventually disappear.

Influence of dislocation stress field on distribution of quantum dots

InAs quantum dots (QDs) were grown on In0.15Ga0.85As strained layers by molecular beam epitaxy on GaAs (0 0 1) substrates. Atomic force microscopy and transmission electron microscopy study have indicated that In0.15Ga0.85As ridges and InAs QDs formed at the inclined upside of interface misfit dislocations (MDs). By testifying the MDs are mixed 60 degrees dislocations and calculating the surface stress over them when they are 12-180 nm below the surface, we found the QDs prefer nucleating on the side with tensile stress of the MDs and this explained why the ordering of QDs is weak when the InGaAs layer is relatively thick. (c) 2006 Elsevier B.V. All rights reserved.

The role of Sb in the molecular beam epitaxy growth of 1.30-1.55 mu m wavelength GaInNAs/GaAs quantum well with high indium content

Sb-assisted GaInNAs/GaAs quantum wells (QWs) with high (42.5%) indium content were investigated systematically. Transmission electron microscopy, reflection high-energy electron diffraction and photoluminescence (PL) measurements reveal that Sb acts as a surfactant to suppress three-dimensional growth. The improvement in the 1.55 mu m range is much more apparent than that in the 1.3 mu m range.. which can be attributed to the difference in N composition. The PL intensity and the full-width at half maximum of the 1.55 mu m single-QW were comparable with that of the 1.3 Am QWs. (c) 2006 Elsevier B.V. All rights reserved.

The effect of AlN growth time on the electrical properties of Al0.38Ga0.62N/AlN/GaN HEMT structures

Al0.38Ga0.62N/AIN/GaN HEMT structures have been grown by metal-organic chemical vapor deposition (MOCVD) on 2-inch sapphire substrates. Samples with AIN growth time of 0s (without AIN interlayer), 12, 15, 18 and 24s are characterized and compared. The electrical properties of two-dimensional electron gas (2DEG) are improved by introducing AIN interlayers. The AIN growth time in the range of 12-18s, corresponding to the AIN thickness of 1-1.5 nm, is appropriate for the design of Al0.38Ga0.62N/AIN/GaN HEMT structures. The lowest sheet resistance of 277 Omega sq(-1) and highest room temperature 2DEG mobility of 1460 cm(2)V(-1) s(-1) are obtained on structure with AIN growth time of 12s. The structure with AIN growth time of 15s exhibits the highest 2DEG concentration of 1.59 x 10(13) cm(-2) and the smallest RMS surface roughness of 0.2 nm. (c) 2006 Elsevier B.V. All rights reserved.

Room-temperature observation of electron resonant tunneling through InAs/AlAs quantum dots

Molecular beam epitaxy is employed to manufacture self-assembled InAs/AlAs quantum-dot resonant tunneling diodes. The resonant tunneling current is superimposed on the thermal current, and together they make up the total electron transport in devices. Steps in current-voltage characteristics and peaks in capacitance-voltage characteristics are explained as electron resonant tunneling via quantum dots at 77 or 300 K, and thus resonant tunneling is observed at room temperature in III-V quantum-dot materials. Hysteresis loops in the curves are attributed to hot electron injection/emission process of quantum dots, which indicates the concomitant charging/discharging effect. (c) 2006 The Electrochemical Society.

Optical properties of inGaAs/GaAs quantum wells grown by Sb-assisted molecular beam epitaxy

It is found that both methods using either continuous Sb supply or pre-deposition of a very thin Sb layer are efficient for the Sb-assisted molecular beam epitaxy growth of highly strained InGaAs/GaAs quantum wells (QWs). The emission of QWs is extended to long wavelength close to 1.25 mu m with high luminescence efficiency at room temperature. The influence of rapid thermal annealing (RTA) on the photoluminescence intensity critically depends on the annealing temperature and duration for highly strained QWs. A relatively low RTA temperature of 700 degrees C with a short duration of 10 s is suggested for optimizing the annealing effect. (c) 2005 Elsevier B.V. All rights reserved.

Magnetron sputtering growth of InAs0.3Sb0.7 films on (100) GaAs substrates: Strong effect of growth conditions on film structure

The growth of highly lattice-mismatched InAs0.3Sb0.7 films on (100) GaAs Substrates by magnetron Sputtering has been investigated and even epitaxial lnAs(0.3)Sb(0.7) films have been successfully obtained. A strong effect of the growth conditions on the film structure was observed, revealing that there was a growth mechanism transition from three-dimensional nucleation growth to epitaxial layer-by-layer growth mode when increasing the substrate temperature. A qualitative explanation for that transition was proposed and the critical conditions for the epitaxial layer-by-layer growth mode were also discussed. (c) 2005 Elsevier B.V. All rights reserved.

Optical properties of self-assembled InAs/InAlAs/InP quantum wires with different InAs deposited thickness

We report on the photoluminescence (PL) properties of InAs/InAlAs/InP quantum wires (QWRs) with various InAs deposited thickness. The PL linewidth of the QWRs decreases with increasing InAs deposited thickness due to the different thicknesses of the QWRs and defects in the samples. The defects and lateral composition modulation of the InAlAs layers play an important role in the temperature-dependent PL properties of the samples. (c) 2005 Elsevier B.V. All rights reserved.

Influence of high-temperature AIN buffer thickness on the properties of GaN grown on Si(111)

The influences of AlN buffer thickness on the optical and the crystalline properties of metalorganic chemical vapor deposition wurtzite GaN layers on Si(I 11) substrate have been investigated. High-resolution X-ray diffraction and photoluminescence measurement reveal that the thickness of AlN buffer exerts a strong influence on the distribution of dislocation and stress in GaN epilayer. The evidence is further reinforced by atomic force microscopic observation of AlN nucleation process. The optimum thickness of AlN buffer to effectively suppress Si diffusion has been determined by secondary-ion mass spectroscopy to be in the range of 13-20 nm. In addition, it is found that appropriate Si diffusion in AlN buffer helps to compensate the tensile strain in GaN, which subsequently improves the optical quality of GaN on Si(I 1, 1), and reduces the cracks over the GaN surface. (C) 2003 Elsevier B.V. All rights reserved.

In0.25Ga0.75As films growth on the thin GaAs/AlAs buffer layer on the GaAs(001) substrate

Thin GaAs/AlAs and GaAs/GaAs buffer layer structure have been fabricated on the GaAs(001) substrate. The top GaAs buffer layer is decoupled from the host substrate by introduction of a low temperature thin interlayer (AlAs or GaAs), which was mechanically behaved like the compliant substrate. Four hundred nanometer In0.25Ga0.75As films were grown on these substrates and the traditional substrate directly. Photoluminescence (PL), double-crystal X-ray diffraction (DCXRD) and atomic force microscopy (AFM) measurements were used to estimate the quality of the In0.25Ga0.75As layer and the compliant effects of the low temperature buffer layer. All the measurements shown that the qualities of epilayer have been improved and the substrate have been deteriorated severely. The growth technique of the thin GaAs/AlAs structure was found to be simple but very powerful for heteroepitaxy. (C) 2003 Elsevier Science B.V All rights reserved.

GaN1-xPx ternary alloys with high P composition grown by metal-organic chemical vapor deposition

GaN1-xPx ternary alloys with high P compositions were deposited on sapphire substrates by means of metal-organic chemical vapor deposition. Depth profiles of the elements indicate that the maximum P/N composition ratio is about 17% and a uniform distribution of the P atoms in the alloys is achieved. 2theta/omega XRD spectra demonstrate that the (0002) peak of the GaN1-xPx alloys shifts to smaller angle with increasing P composition. From the photoluminescence (PL) spectra, the red shifts to the bandedge emission of GaN are determined to be 73, 78, 100 and 87 meV for the GaN1-xPx alloys with the P/N composition ratios of 3%, 11%, 15% and 17%, respectively. No PL peak related to GaP is observed, indicating that the phase separation between GaN and GaP is well suppressed in our GaN1-xPx samples. (C) 2003 Elsevier Science B.V. All rights reserved.