Effects of crystallinity and chemical variation on apparent band-gap shift in polycrystalline indium nitride

The nature of the apparent band-gap shift in polycrystalline indium nitride thin-films, grown by remote-plasma-enhanced chemical vapour deposition at 535 ± 10 °C, has been investigated separately in relation to growth temperature dependent crystallinity and chemical variation. Substrates of sapphire and gallium nitride on sapphire were used to study the effect of a stress-reduced template on indium nitride crystallite quality and apparent band-gap. To mimic surface growth temperature variations two glass substrates of differing thickness and thermal conductivity were intentionally used for the same growth conditions. The samples were characterised using optical transmission, scanning electron microscope, X-ray diffraction, and high-resolution X-ray photoelectron spectroscopy. The results indicate that the apparent band-gap shift in polycrystalline narrow band-gap indium nitride thin-films is not primarily determined by the quality of indium nitride crystallites but rather it is associated with growth temperature dependent chemical variations in the films.     

Investigation of indium oxide as a self-catalyst in ZnO/ZnInO heterostructure nanowires growth

We investigated the self-catalytic role of indium oxide in the growth process of ZnO/ZnInO heterostructure nanowires on Si(111). The prepared nanowires had hexagonal cross sections and were tapered with tip diameters of 90 ± 5 nm and base diameters of 230 ± 5 nm. Energy dispersive X-ray and field emission Auger spectroscopies indicated that the grown nanowires were heterostructures of ZnO and ZnInO. Analysis of the early growth process revealed that indium may play a self-catalytic role. Therefore, the vapor-liquid-solid mechanism is likely to be responsible for growth of ZnO/ZnInO nanowires. X-ray diffraction and room temperature photoluminescence (PL) data demonstrated that the presence of indium results in a decrease in nanowires' crystallinity. These wires produced a large PL emission peak in the ultraviolet (UV) region and a smaller peak in the green region of the electromagnetic spectrum. The UV peak of the ZnO/ZnInO nanowires is blue-shifted with respect to that of pure ZnO nanowires.     

Investigation on the role of indium in the removal of metallic gallium from soft and hard sputtered GaN (0001) surfaces

Cleaning of GaN by argon sputtering and subsequent annealing introduces metallic gallium on the GaN surface. Once formed, this metallic gallium can be difficult to remove. It has a strong influence on the Fermi level position in the band gap and poses a problem for subsequent epitaxial growth on the surface. We present a method of removing metallic gallium from moderately damaged GaN surfaces by deposition of indium and formation of an In-Ga alloy that can be desorbed by annealing at ~ 550 °C. After the In-Ga alloy has desorbed, photoemission spectra show that the Ga3d bulk component becomes narrower indicating a smoother and more homogeneous surface. This is also reflected in a sharper low energy electron diffraction pattern. On heavily damaged GaN surfaces, caused by hard sputtering, larger amount of metallic gallium forms after annealing at 600 °C. This gallium readily alloys with deposited indium, but the alloy does not desorb until a temperature of 840 °C is reached and even then, traces of both indium and metallic gallium could be found on the surface.     

Thermophysical properties of polyvalent metals and their alloys in the solid and liquid states

Resistivity, thermal conductivity, and ultrasound velocity for the metals of the third group, namely, gallium, indium, and thallium are given in a temperature range from 300 to 1000°K as well as resistivity and thermal conductivity of indium-thallium and thallium-tin alloy systems in wide temperature and concentration ranges.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 4, pp. 614–620, April, 1980.     

Chemical beam epitaxial growth of GaInP using uncracked trisdimethylaminophosphine

Gallium indium phosphide (Ga _x In_1−x P) epitaxial layers were grown on GaAs substrates by chemical beam epitaxy (CBE) without thermally precracking the group V precursor. Trisdimethylaminophosphine (TDMAP), triisopropylgallium (TIPGa), and ethyldimethylindium (EDMIn) were used as the phosphorus, gallium and indium sources, respectively. Ga _x In_1−x P was grown without group V precracking for substrate temperatures in the range of 400–520 °C. Above 500 °C, the epilayers had a hazy appearance presumably due to being phosphorus deficit. A strong solid composition dependence on substrate temperature was observed. The samples were In-rich at low growth temperatures and Ga-rich at high growth temperatures. It was possible to grow the Ga _x In_1−x P epilayers over a large composition range with good morphology and strong photoluminescence. Values of full width at half maximum were as low as 45 meV at 14 K photoluminescence measurements.     

Effect of substrate temperature on the physical properties of In2O3:Mo films: Prepared by an activated reactive evaporation

Transparent and high conductive molybdenum doped indium oxide (IMO) thin films have been deposited on glass substrates by activated reactive evaporation. The effect of substrate temperature on the structure, surface morphology, electrical, optical and photoluminescence properties of these films were systematically examined and it was found that crystallinity and growth orientation of the films were significantly influenced by substrate temperature. In addition the films exhibited a low electrical resistivity of 5.2 × 10⁻⁴ Ω cm with an optical transmittance 90% in the visible region of the solar spectrum at a substrate temperature of 573 K. Intensive blue PL bands at 415 and 440 nm were observed in the photoluminescence spectrum at room temperature.     

Structural properties of Cu(In,Ga)Se2 thin films prepared from chemically processed precursor layers

We have developed a chemical process for incorporating copper into indium gallium selenide layers with the goal of creating a precursor structure for the formation of copper indium gallium diselenide (CIGS) photovoltaic absorbers. Stylus profilometry, EDX, Raman spectroscopy, XRD and SIMS measurements show that when indium gallium selenide layers are immersed in a hot copper chloride solution, copper is incorporated as copper selenide with no increase in the thickness of the layers. Further measurements show that annealing this precursor structure in the presence of selenium results in the formation of CIGS and that the supply of selenium during the annealing process has a strong effect on the morphology and preferred orientation of these layers. When the supply of Se during annealing begins only once the substrate temperature reaches ≈ 400 °C, the resulting CIGS layers are smoother and have more pronounced preferred orientation than when Se is supplied throughout the entire annealing process.     

Temperature dependences of longitudinal ultrasonic wave propagation velocity in gallium arsenide and indium phosphide single crystals

Results are considered for experimental studies of the longitudinal ultrasonic wave propagation velocity in gallium arsenide <001> and indium phosphide <100> single crystals in the temperature range 200–355 K with measurements made through each 0.5–1 K. Measurements were made by the ultrasonic echo-pulse procedure using calibration marks of time. The frequency of the sounding signal is 10 MHz.Translated from Problemy Prochnosti, No. 11, pp. 48–49, November, 1991.     

Method of obtaining gallium from aluminate solution by electrolysis

Abstract

Gallium is an increasingly important material in the fields of semiconductors and energy transfer. A prime source of gallium is the aluminate solution that remains after the purification of bauxite. The authors have sought a way of reclaiming gallium economically by electrolysis of a laboratory aluminate solution without having to use a cathode of mercury – an environmental pollutant. Cathodes of copper, indium, 70In–30Ga, Wood's alloy, and mercury (for comparison) were used with a wide range of anodes. The study accounted for the effects of electrode material, temperature, current density, and initial gallium concentration on the yield, energy consumption, and utilization of both current and electrode. The best results were obtained with indium or In–Ga cathodes and with platinum, Pt–Ti, or stainless steel anodes, at 75°C and a current density of ~100 Am^?2. Electrolysis was more efficient the higher the gallium concentration, demonstrating that commercial–scale electrolysis of aluminate solution is unlikely to be economically viable without prior concentration of gallium.

MST/305     

The impact of trimethylindium treatment time during growth interruption on the carrier dynamics of InGaN/GaN multiple quantum wells

Solid-state lighting through light emitting diodes (LEDs) is considered the next generation white-lighting. Because green light affects the quality of white light, significant improvement of the luminescence efficiency of green InGaN LEDs are crucial. In this study, the effects of trimethylindium (TMIn) treatment time during growth interruption on the emission and carrier dynamic characteristics of InGaN/GaN multiple quantum wells with green emission were investigated. TMIn treatment during growth interruption suppresses InGaN decomposition and indium aggregation such that more homogeneous indium composition, higher effective potential level, higher energy (localized) states, stronger photoluminescence (PL) intensity, and an apparent S-shaped variation of the temperature-dependent PL peak position were observed. In addition, as the treatment time increases, the decay time and its variation both become smaller. Because indium composition within the InGaN quantum wells is more homogeneous the longer the treatment time, weaker carrier transport and carrier-localized effects lead to a shorter decay time and better recombination efficiency. The research results provide important information to optimize the performance of green and white LEDs.     

Effects of cracker cell temperature and V/III ratio on GaInP grown by chemical beam epitaxy using TIPGa, EDMIn and TBP

This paper reports a systematic study of the effects of the cracker cell temperature and the input V/III ratio on the growth of GaInP. GaInP epilayers were grown on GaAs (001) substrates using triisopropylgallium, ethyldimethylindium and tertiarybutylphosphine by chemical beam epitaxy. The surface morphology, growth rate, low temperature (15 K) and room temperature (300 K) photoluminescence (PL) were studied as a function of the cracker cell temperature and input V/III ratio. At an optimum cracker cell temperature and input V/III ratio, the PL spectrum showed only a strong band edge peak with a full width at half maximum of 10.8 meV.     

Investigation of V-defects formation in InGaN/GaN multiple quantum well grown on sapphire

In the growth of InGaN multiple quantum well structure, V-pits has been observed to be initiated at the threading dislocations which propagate to the quantum well layers with high indium composition and substantially thick InGaN well. A set of samples with varying indium well thickness (3-7.6 nm) and composition (10-30%) are grown and characterized by photoluminescence (PL), X-ray diffraction, transmission electron microscopy and atomic force microscopy. The indium content and the layer thicknesses in InGaN/GaN quantum well are determined by high-resolution X-ray diffraction (XRD) and TEM imaging. With indium composition exceeding 10%, strain at the InGaN/GaN interface leads to the generation of V-pits at the interlayers of the MQW. Higher indium composition and increase in thickness of a period (InGaN well plus the GaN barrier) appear to enhance pits generation. With thicker InGaN well and reduction in thickness of GaN to InGaN (or the R ratio), pit density is substantially reduced, but it results in greater inhomogeneity in the distribution of indium in the InGaN well. This leads to a broadened PL emission and affect the PL emission intensity.     

Chemical Interaction of Indium Arsenide and Gallium Antimonide with Sulfur

The reactions of fine-particle indium arsenide and gallium antimonide with sulfur and the composition of the reaction products obtained from different starting mixtures were studied by differential thermal analysis, x-ray diffraction, chemical analysis, and IR spectroscopy. The reaction between indium arsenide and sulfur begins at lower temperatures in comparison with gallium antimonide, is autocatalyzed, and yields In₂S₃ and As₂S₃. The reaction between gallium antimonide and sulfur yields Ga₂S₃, Sb₂S₃, and (GaS)₂. Thermolysis of the resultant sulfide mixtures ensures a more complete separation of the sulfides in the case of indium arsenide.     

Chemical Vapor Deposition of GaN from Gallium and Ammonium Chloride

Thick polycrystalline gallium nitride films were grown by a two-step chemical vapor deposition process using gallium metal and ammonium chloride as starting reagents, at deposition rates of up to 50 m/h. The deposits were examined by scanning electron microscopy and photoluminescence (PL) spectroscopy. The results demonstrate that the proposed process can be used to grow high-quality, stoichiometric gallium nitride layers with a perfect crystal structure, as evidenced by the high intensity of the 380-nm exciton peak in the room-temperature PL spectra of the films and also by electron-microscopic examination.     

Transformation of InAs islands to quantum ring structures by metalorganic vapor phase epitaxy

The transformation of InAs islands to quantum rings (QRs) by metalorganic vapor phase epitaxy is investigated. After covering the InAs islands with a thin GaAs partial capping layer and annealing under tertiarybutylarsine (TBAs) flow, ring-shaped nanostructures with a density of 10(7)-10(9)?cm(-2) are obtained at 500-600?°C. The effects of the growth temperature, annealing process and thickness of the partial capping layer are studied. Optimum values for the annealing time and the partial capping layer thickness were found to be 60-120?s and 0.5-2.0?nm, respectively. Low temperature photoluminescence (PL) emission peaks from islands and QRs grown at 500?°C are observed at 1.04?eV and 1.22?eV, respectively. The annealing temperature affected the QR evolution and the PL emission from the QRs due to the temperature dependence of the diffusion rate of indium atoms.     

The kinetics of transformation in amorphous germanium alloy films

The kinetics of the amorphous-to-crystalline transformation were studied in amorphous germanium (a-Ge) and its alloys with aluminium, silicon, indium, copper, iron, nickel, gallium and tin by using isochronal and isothermal annealing of the room temperature resistivity, differential thermal analysis and electron microscopy measurements. It was shown that the transformations in a-Ge and a-Ge alloy films are nucleation and growth controlled. The activation energy of 3.0 eV obtained for the amorphous-to-crystalline transition in a-Ge was found to decrease on alloying with metals, and the decrease depended on the nature of the alloying element.     

Comparative study on early stages of film growth for transparent conductive oxide films deposited by dc magnetron sputtering

Early stages of film growth were investigated on three different kinds of representative transparent conductive oxide films including tin doped indium oxide (ITO), indium zinc oxide (IZO) and gallium doped zinc oxide (GZO) films deposited on unheated alkali free glass substrates by dc magnetron sputtering. The variations in sheet resistance, film coverage and average surface roughness showed clearly that ITO and GZO films possessed Volmer-Weber growth mode. In contrast, the evolution of islands is not clearly observed for IZO film. The nucleation density of IZO film is considered to be much higher than that of ITO and GZO films.     

Indium oxide thin film based ammonia gas and ethanol vapour sensor

A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temperature. The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included in this paper.     

Thermal Expansion and Some Characteristics of the Interatomic Bond Strength in Gallium and Indium Phosphides

A thermometric method is used to determine the thermal expansion coefficient of an InP melt in the temperature range of 1331–1426 K. A statistical treatment and a thermodynamic analysis of the thermal expansion coefficients for solid gallium and indium phosphides are performed using the relevant data on heat capacity. As a result, it is possible to recommend the most reliable values of the thermal expansion coefficient for these compounds in a wide temperature range. Based on these recommended data, the characteristic values of the Debye temperature and of the root-mean-square displacement of atoms from the equilibrium position are calculated, and the results are compared with the respective values obtained by other methods.     

Thermal dissociation of InP covered with metallic contact layers

InP samples covered with mainly gold and gold-based metallizations were heat treated in a vacuum and the evolution of volatile components was monitored in situ with a mass spectrometer. Gold greatly enhances the decomposition of InP: saturation of the gold film with indium takes place and the phosphorus evaporates so that a peak or peaks appear on the out-evaporation versus temperature curve. The thinner the gold layer, the lower are the temperature of peak phosphorus evolution and the total phosphorus loss. The presence of additional indium or gallium decreases the evolution of phosphorus. Gold-based ohmic contact metallizations also induce large volatile component losses.