AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires modified gate exhibit significant changes in channel conductance upon exposure to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition, with perfect crystal quality will attach CO molecules and release electrons, which will lead to a change of surface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasing the piezo-induced charge density in the HEMTs channel. These electrons create an image positive charge on the gate region for the required neutrality, thus increasing the drain current of the HEMTs. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm and 3200 ppm in the open cavity with continuous gas flow using a 50 × 50 μm2 gate sensing area for polar and nonpolar ZnO nanowire gated HEMTs sensor, respectively.

Zinc oxide (ZnO) thin film was grown on semi-insulating Si substrate using arsine (AsH3) as precursor by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD). In recently reported results, the physical mechanisms for As-doped ZnO thin films are explained as As substitution for oxygen (AsO) or As substitution for Zn and As combined with two Zn vacancies (AsZn2VZn). In this study, we control the in situ annealing ambient into two environments with various temperatures, which are Zn-rich, using diethylzinc (DEZn) as ambient gas, and O-rich, using water vapor as ambient gas, respectively. This should help to create AsO and AsZn2VZn. The ZnO thin film after in situ thermal annealing with H2O vapor ambient at 550 and 750 degrees C show p-type conductivity with hole concentration of 2.651 x 10(17) and 1.782 x 10(18)?cm-3, Hall mobilities of 10.08 and 5.402?cm2/V?s, and resistivities of 2.368 and 0.6485?O?cm, respectively.

This study attempted to grow single-phase γ-In2Se3 nanorods on Si (111) substrates by metal-organic chemical vapor deposition (MOCVD). High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) confirmed that the In2Se3 nanorods are singularly crystallized in the γ phase. The photoluminescence of γ-In2Se3 nanorods at 15 K was referred to as free and bound exciton emissions. The bandgap energy of γ-In2Se3 nanorods at room temperature was determined to be ~1.99 eV, obtained from optical absorption.

The energy relaxation of hot electrons in ZnO films was investigated by the electric-field-dependent photoluminescence. From the high-energy tail of photoluminescence, the electron temperature of the hot electrons in ZnO was determined. Longitudinal optical phonon emission alone cannot explain the relationship between the electron temperature and the electron energy loss rate. Instead, it can be explained by a model based on a combination of both the acoustic and longitudinal optical phonon emissions.

The single-phase γ-In2Se3 films with red room-temperature photoluminescence (PL) have been realized by atmospheric metal-organic chemical vapor deposition at the temperature range of 350–500°C. The crystal structure of the γ-In2Se3 films was determined by X-ray diffraction and Raman spectroscopy. From the temperature dependence of the free exciton line, the room-temperature energy gap of γ-In2Se3 films is found to be about 1.947eV. At 10K, the free exciton emissions was observed and located at 2.145eV. The temperature dependence of the near band-edge emission in the temperature region of 10–300K has been investigated. The measured peak energy of near band-edge emission redshifts by about 200meV with increasing temperature from 10 to 300K, and is expressed by, Eg(T)=2.149+((−8.50×10−4)T2/(T+75.5))eV. This study was done to complete the reported information about γ-In2Se3 thin films.

The single-phase gamma-In2Se3 films with red room-temperature photoluminescence (PL) have been realized by atmospheric metal-organic chemical vapor deposition at the temperature range of 350-500 degrees C. The crystal structure of the gamma-In2Se3 films was determined by X-ray diffraction and Raman spectroscopy. From the temperature dependence of the free exciton line, the room-temperature energy gap of gamma-In2Se3 films is found to be about 1.947 eV. At 10K, the free exciton emissions was observed and located at 2.145 eV. The temperature dependence of the near band-edge emission in the temperature region of 10-300K has been investigated. The measured peak energy of near band-edge emission redshifts by about 200 meV with increasing temperature from 10 to 300K, and is expressed by, E-g(T) = 2.149 + ((-8.50 x 10(-4))T-2/(T + 75.5)) eV. This study was done to complete the reported information about gamma-(InSe3)-Se-2 thin films. (C) 2010 Elsevier B.V. All rights reserved.

In this study, III-nitride solar cells with multi-quantum well (MQW) absorption layer were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). The effect of different quantum well (QW) arrangement on optoelectronic characteristics of III-nitrides photovoltaic cells was investigated. It was found that the upper quantum well (QW) layer will dominate electroluminescence (EL) emission mechanism and the electrical characteristics of solar cell. The advantage of modulating the short-circuit current density (J(SC)) and open-circuit voltage (V-OC) can be obtained by different arrangement of blue and green QW in MQW absorption layer. The optimum electrical characteristics of solar cell with a J(SC) of 0.30 mA/cm(2), a V-OC up to 1.51 V, fill factor (FF) as high as 0.601, and a series resistance (R-S) of 9 Omega can be obtained by using MQW absorption layer. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Heteroepitaxial ZnO epilayers were grown on Si(1 1 1) substrates using a vertical geometry atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) system. The growth temperature was varied from 550 degrees C to 650 degrees C in steps of 25 degrees C. The ZnO growth rate and surface morphology were strong functions of the growth temperature and ranged from similar to 0.16 mu m/h to 1.36 mu m/h. The surface morphology of the ZnO films changed from granular to sharp tips as the growth temperature increased. The effect of buffer thickness was also examined, and was found to have a strong effect on the optical properties of the ZnO. An optimized growth condition for ZnO epilayers was found at 625 degrees C, producing a FWHM in the room temperature photoluminescence (PL) spectrum of 4.5 nm and a preferred growth orientation along the (0 0 2) direction.Transmission electron microscopy images and selected area diffraction patterns showed excellent crystalline quality of both the buffer and ZnO overlayer. When non-optimized growth temperatures were employed, post-growth annealing was found to greatly enhance the ratio of band-edge to deep level emission. (C) 2009 Elsevier B.V. All rights reserved.

Indium nitride (InN) dots grown on sapphires by metal organic chemical vapor deposition (MOCVD) with an In0.08Ga0.92N intermediate layer were demonstrated. Inserting an In0.08Ga0.92N layer between InN and GaN reduced the average size of InN dots, increased the density of InN dots, and prevented the formation of polycrystalline InN or metallic indium. Furthermore, blue shift of the photoluminescence spectrum of InN dots can be identified when inserting an In0.08Ga0.92N intermediate layer, likely because the InN dots with an In0.08Ga0.92N intermediate layer are markedly smaller than InN dots without an In0.08Ga0.92N intermediate layer, indicating the size quantization effect in the dots.

Undoped zinc oxide (ZnO) thin films were deposited on Si (100) substrates by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD). After a nucleation layer of ZnO about 500 Å was deposited, top ZnO films with 320–440 nm in thickness were fabricated at temperatures varying from 450 to 600 °C, respectively. X-ray diffraction analyses demonstrate that all the films grown have polycrystalline wurtzite structure. Scanning electron microscopy observations indicate that ZnO films grow with c-axis aligned grains when the deposition temperature is lower than 600 °C. However, 3D microstructures without c-axis alignment were found when the film was deposited at 600 °C. Room temperature photoluminescence (PL) spectra peaking at 3.27–3.29 eV were observed for the ZnO films grown at 450–600 °C. However, only the spectrum from the film grown at 600 °C could present a high intensity ratio of the ultraviolet band to deep-level emissions, which is above 392 and show a minimum full-width at half-maximum of 99 meV for the ultraviolet band. Temperature-dependent PL measurements from 20 to 300 K exhibited the luminescent mechanism of the present ZnO films to be near band excitonic emission.

The surface morphology of ZnO grown on p-GaN templates and p-Si (111) substrates at various temperatures by metal organic chemical vapor deposition (MOCVD) in a vertical reactor at atmospheric pressure is reported. A low temperature ZnO buffer was deposited initially at 200°C for 15min as a nucleation layer. Epitaxial ZnO was grown at 500°C, 550°C, 600°C for 40min, respectively. Uniformly distributed and well-aligned ZnO nanorods with diameter in the range 80–120nm and length ∼0.7μm were observed for deposition on p-GaN template. By contrast, the morphology of ZnO epilayers grown on p-Si (111) transitioned from 2D to 3D with increasing growth temperature. X-ray diffraction (XRD) spectra showed all the ZnO epilayers had the hexagonal wurtzite structure but different preferred orientation. PL spectra showed only free-exciton emission at 378nm (∼3.28eV) with a full width at half maximum of 13nm without defect-related green emission in the epitaxial ZnO grown at 550°C and 600°C. The epitaxial ZnO layers grown on p-GaN and p-Si at the same temperature have similar PL spectra. The PL measurement also exhibits strong exciton-related emission without defect peak, which showed that the ZnO nanostructures grown at 550°C and 600°C have good optical properties with excellent crystal quality.

The energy relaxation of electrons in γ-In2Se3nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature (Te) of the hot electrons. TheTevariation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In2Se3nanorods may be a promising material for the photovoltaic devices.

Photoluminescence (PL) of Si nanocrystals with annealing in CO2 was studied using the continuous and time-resolved PL measurements. The PL intensity enhances as annealing temperature increases, which is attributed to passivation of the nonradiative recombination centers. As the annealing temperature is 950°C the PL intensity has a maximum value, which increases about a factor of 3 than that of the untreated sample. Based on the emission energy dependence of the PL decay time, the depth of carrier localization is found to increase after the annealing in CO2. We suggest that the oxygen atoms desorbed from CO2 diffuse to react with Si nanocrystals and introduce localized states at the Si/SiO2 interface.

InN quantum dots (QDs) were grown over 2in. Si (1 1 1) wafers with a 300nm thick AlN buffer layer by atmospheric-pressure metal organic vapor phase epitaxy. When the growth temperature increased from 450to625°C, the corresponding InN QDs height increased from 16to108nm while the density of the InN QDs decreased from 1.6×109cm−2to3.3×108cm−2. Transmission electron microscopy showed the presence of a 2nm thick wetting layer between the AlN buffer layer and InN QDs. The growth mechanism was determined to be the Stranski–Krastanov mode. The presence of misfit dislocations in the QDs indicated that residual strain was introduced during InN QDs formation. From x-ray diffraction analysis, when the height of the InN QDs increased from 16to62nm, the residual strain in InN QDs reduced from 0.45% to 0.22%. The residual strain remained at 0.22% for larger heights most likely due to plastic relaxation in the QDs. The critical height of the InN QDs for releasing the strain was determined to be 62nm.

A study of thermally stimulated currents (TSC) is applied to alpha-HgI2 polycrystalline films grown by physical vapour deposition with various thermal boundary conditions. Five TSC peaks are clearly observed and numerically fitted. The activation energy and the density of the trapping centre that corresponds to each TSC peak are then calculated. Finally, the effects of the deposition conditions on the TSC results are discussed.

We have investigated the photoluminescence (PL) and time-resolved PL from the InN epilayers grown on Si substrates with different buffer layers. The narrowest value of the full width at half maximum of the PL peak is 52 meV with the AlN/AlGaN/GaN triple buffer layer, which is better than previous reports on similar InN epilayers on Si substrates. Based on the emission-energy dependence of the PL decays, the localization energy of carriers is also the least for the InN with a triple buffer layer. According to the x-ray diffraction measurements, we suggest that the reduced lattice mismatch between the InN epilayer and the top buffer layer is responsible for improvement of sample quality using the buffer-layer technique.

A study of thermally stimulated currents (TSC) is applied to α-HgI2 polycrystalline films grown by physical vapour deposition with various thermal boundary conditions. Five TSC peaks are clearly observed and numerically fitted. The activation energy and the density of the trapping centre that corresponds to each TSC peak are then calculated. Finally, the effects of the deposition conditions on the TSC results are discussed.

A set of In2Se3 films was grown on (111) Si substrate with AlN buffer by metalorganic chemical vapor deposition (MOCVD) using H2Se as the metalogramic precursors for Se. The In2Se3 films on (111) Si substrate were pinhole-free with homogeneous and lamellar structures. It was found that by properly controlling the substrate temperatures, single-phase γ-In2Se3 films with fairly good optical properties can be well fabricated. Photoluminescence spectra of single-phase γ-In2Se3 show exciton emissions at 2.140eV at 10K. The band gap of single-phase γ-In2Se3 at room temperature is estimated at 1.943eV.

The carrier localization in InN epilayers grown on Si(111) was studied using time-resolved photoluminescence (PL). The emission energy dependence and temperature dependence of the PL decay times revealed that carrier localization plays an important role in the recombination of this material system. A model based on the transition between free electrons in the conduction band and localized holes in the deeper tail states explains the carrier localization of InN epilayers. We suggest that the carrier localization in InN can be accounted for by the potential fluctuation caused by the random impurities.

Single-crystalline GaN films were grown on Si(111) substrates by metal organic chemical vapor deposition (MOCVD) using a silicon nitride (SiNx) buffer achieved through the nitridation of substrate. The effect of in situ substrate nitridation on the GaN crystalline quality was investigated with the nitridation being performed at 750, 950 and 1120°C, respectively. It demonstrates that the nitridation temperature greatly influences the surface morphology and PL spectra of GaN grown atop SiNx buffer. The surface roughness of GaN film grown atop the Si substrate nitridated at 950°C exhibited a root mean square (RMS) value of 5.057nm for surface roughness evaluated by atomic force microscopy (AFM). Additionally, a strong photoluminescence (PL) emission at 365nm (3.4eV) with the full-width at half-maximum (FWHM) of 61.1meV was achieved at room temperature. Particularly, a yellow luminescent band that was observed when the nitridation was performed at 750°C was greatly reduced to a degree that could hardly be recognized. Alternatively, nitridating the substrate at 1120°C resulted in a strong but much wider PL spectrum. Accordingly, an effective buffer of SiNx for the growth of GaN on Si substrates can be formed by introducing the substrate nitridation at a due temperature around 950°C before the commencement of epitaxial growth.