Pressure Metalorganic Vapor Phase Research Articles

Effect of the lower and upper interfaces on the quality of InAs/GaAs quantum dots

The aim of this work is to influence quantum dot (QD) formation by improving the lower and upper InAs/GaAs QD interface quality. QD properties were studied by reflectance anisotropy spectroscopy, atomic force microscopy and high resolution transmission electron microscopy. All structures were prepared by low pressure metal organic vapor phase epitaxy.Concerning the lower interface, a good epitaxial surface planarity is required for QD formation with high QD density and narrow size distribution. Therefore the growth conditions of the QD buffer layer are very important. We demonstrate the improvement of the QD size distribution and homogeneity, when the growth rate of the buffer layer was decreased.The upper QD interface is formed during the covering process. InAs quantum dots were capped by GaAs or by GaAsSb. The presence of Sb atoms in covering layer strongly influences the interface abruptness. In the case of GaAs covering layer, an InGaAs layer with gradual decrease of In concentration is unintentionally formed at the interface between InAs and GaAs. The presence of Sb in GaAsSb covering layer helps to form abrupt interface between InAs and covering layer. However, enhanced surfacting of In atoms was observed for GaAsSb SRL. An optimal GaAsSb composition profile is suggested to prevent dissolution of QDs during the covering process and to minimize the amount of surfacting In atoms.

Comparison of optoelectronic properties of InAs/GaAs quantum dots grown under different conditions by metalorganic vapor phase epitaxy

InAs/GaAs quantum dots were grown by atmospheric pressure metalorganic vapor phase epitaxy in different technological conditions. A comparative study of influence of growth parameters on their optoelectronic properties was performed. It was found that the energy spectrum of InAs quantum dots grown in the regime with increased interruption time between chemical reagents flows has low sensitivity to the modifications of GaAs cladding layer thickness and the presence of InGaAs quantum well.

Effect of growth temperature and GaAs substrate misorientation on the morphology of InAsBi nanoislands grown by metalorganic vapor phase epitaxy

The structural properties of InAsBi nanoislands grown on semi insulating GaAs by atmospheric pressure metalorganic vapor phase epitaxy, using trimethyl indium, trimethyl bismuth, and arsine as precursor sources have been studied. The influence of growth temperature and substrate misorientation on the surface morphologies of these nanostructures have been controlled by means of atomic force microscopy. The results show InAsBi islands formation on the studied samples. The density, shape, size and the size dispersion of these islands vary greatly with growth temperature. So, below 400°C island density increases with increasing growth temperature and accompanied by appearance of ridges. Increasing temperature over 400°C induces a decrease in the island density and enlargement of sizes. In addition, samples grown on 10° misoriented substrates exhibit a clearly ridge on the surface.

Current injected spectrum change in flat‐topped InAs/InP QD arrayed waveguide LED with different QD heights

AbstractWe have investigated the current injected spectrum of flat‐topped LED using self‐assembled Stranski‐Krastanov (S‐K) InAs/InP quantum dots (QDs) grown by selective area low pressure metalorganic vapor phase epitaxy and a double‐capping procedure. Selective area growth using an SiO2 mask with narrow stripes was carried out to tailor a wide emission range for the QDs in sixteen arrayed waveguides. Each waveguide core con‐tained three stacked QD layers with different QD heights and Ga content in the GaInAs buffer layer. We have measured the spectrum change of current injection, and have estimated the intensity variation in each QDs layer. By increasing the FCL thickness of three QDs layers, output intensity of each layer has become equal, and we have obtained more than 500 nm spectrum width with flat‐topped spectrum shape. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Determination of indium and nitrogen contents of InGaAsN quantum wells by HRXRD study supported by BAC calculation of the measured energy gap

Determination of indium and nitrogen content in InGaAsN quantum wells (QWs) is often based on the analysis of high-resolution X-ray diffraction (HRXRD) measurements. The comparison of diffraction curves of two similar samples, with and without nitrogen, together with an assumption of constant indium incorporation efficiency during the growth of layers with and without nitrogen, may lead to a large deviation in the determined In and N content. The HRXRD curve simulations supported by bandgap determination and calculations seem to be a solution of this problem. Comparison of the results achieved from simulated HRXRD curves with the calculations of all QWs transitions measured by contactless electro-reflectance (CER) can lead to reduction of deviations in composition determination of InGaAsN quantum wells. The proposed algorithm was applied for investigation of InGaAsN QWs grown by atmospheric pressure metalorganic vapor phase epitaxy (APMOVPE).

Electro-optical properties of diluted GaAsN on GaAs grown by APMOVPE

In this paper we report on the optical and electrical studies of single GaAs1−xNx epitaxial layers grown on GaAs substrates by means of atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). Three kinds of samples with 1.2 %, 1.6 % and 2.7 % nitrogen content were studied. Optical properties of the layers were investigated with the use of room temperature transmittance and reflectance measurements. Subsequently Schottky Au-GaAs1−xNx contacts were processed and characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements within 80–480 K temperature range. From the I-V and C-V characteristics the ideality factor, series resistance and built-in potential were determined. Obtained diodes can be used for further studies on defects with the use of DLTS method.

Atmospheric-pressure metal–organic vapor-phase epitaxy of GaAsBi alloys on high-index GaAs substrates

We investigated the growth characteristics and properties of GaAsBi layers grown by atmospheric-pressure metal–organic vapor-phase epitaxy on different GaAs substrate orientations. The surface morphology of GaAsBi alloys was investigated by means of scanning electron microscopy. The structural and optical properties of the alloys were examined using high-resolution X-ray diffraction (HRXRD) and photoreflectance spectroscopy, respectively. HRXRD results show that the GaAsBi growth rate was significantly lower on (115)A than on (001), (111)A and (114)A GaAs. The highest Bi content was obtained for GaAsBi layers grown on (115)A GaAs substrates.

Growth of scandium doped GaN by MOVPE

Scandium (Sc) doped GaN layers (GaN:Sc) were grown on SiN treated sapphire substrate by atmospheric pressure metal–organic vapor phase epitaxy (AP-MOVPE) using Tris(cyclopentadienyl)scandium (Cp3Sc) as a scandium precursor. Standard growth conditions of GaN were used with varying Cp3Sc flow rate up to 1000sccm. The growth was in situ monitored by laser reflectometry. GaN coalescence process is significantly influenced by the presence of Cp3Sc. Sc incorporation in GaN is confirmed by secondary ion mass spectrometry (SIMS) measurements. Electron concentration and mobility variations versus Cp3Sc flow rate were studied by room temperature Hall effect measurements. All samples showed n type conductivity. High resolution X-ray diffraction (HRXRD) results showed a slight broadening of rocking curves around symmetric (00.2) reflexions for Sc doped GaN layers with increasing Cp3Sc flow rate. Room temperature photoluminescence (PL) showed a quenching of ultraviolet near band edge emission (UV) by increasing Sc doping level.

Growth of GaInAs/InP MQW using MOVPE on directly-bonded InP/Si substrate

Thin film InP/Si substrate was fabricated using direct wafer bonding technique. GaInAs/InP MQW layers were grown on this substrate by low pressure metalorganic vapor phase epitaxy (MOVPE) growth. Scanning electron microscope (SEM) photographs of the substrate after MOVPE growth show that the MQW layers were grown over the InP/Si substrate, and poly-crystals were observed where the Si substrate was exposed. And we have obtained almost the same photoluminescence (PL) intensity from the GaInAs/InP MQW layers on InP/Si substrate compared to those on InP substrate. According to the X-ray diffraction measurement, a slight tensile strain at the bonded interface due to the difference of thermal expansion coefficient of the InP substrate and Si substrate is observed.

Electrical characterization of the AIIIBV-N heterostructures by capacitance methods

This paper highlights the electrical characterization of three types of the multiple quantum well (MQW) InGaAsN/GaAs heterostructures labelled NI58n, NI59n and NI66n with the nitrogen concentration of about 0.4% and indium content of 12.1%, 13.5% and 13.0%, respectively, using capacitance methods. These MQW InGaAsN/GaAs heterostructures were grown by atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) at various growth conditions. The capacitance-voltage and DLTS measurements of these structures were performed utilizing the measurement system BIORAD DL8000.The CV characteristics measured at different temperatures on all heterostructures show very fine fluctuations of capacitance in the voltage range around 0V, which is suggested to be a result of free carriers’ emission from quantum wells. The absence of GaAs “cap” layer in one of the samples shifted its CV characteristic to lower values of capacity.According to the DLTS measurement it is highly probable that the similar system of defects is present in all samples. The presence of the deep level ET1 is clear in all samples and its parameters were calculated by multi level evaluation (the activation energy of the defect which is approx. ΔET=0.62eV, value of effective capture cross-section of the defect σT is about 10−16cm2, and defects concentration NT is about 1014cm−3).

Impact of the substrate and of the nucleation layer on the properties of AlGaN/GaN HEMTs on SiC

This work reports on the influence of the substrate properties and of the nucleation layer on the growth mode of AlGaN/GaN HEMT (high electron mobility transistor) structures, grown by low pressure metal organic vapour phase epitaxy (LP-MOVPE) on 3in. 4H-SiC and 6H-SiC semi-insulating substrates. In-situ normal incidence reflectance at 633nm and 950nm was used to monitor the evolution of the surface morphology during the growth. The analysis reveals that the growth of the GaN buffer layer on the AlN wetting layer is a critical key step of the process. Reflectance measurements are discussed in term of roughness-related light scattering and absorption. The influence of substrate surface properties has been studied extensively. Physical and electrical properties of the HEMT structures, as evaluated by a complete set of ex-situ characterisation techniques, were found to be strongly influenced by the quality of this interface.A significant improvement of the surface morphology during the growth was obtained by the insertion of an AlGaN/GaN multiquantum well (MQW) between the AlN wetting layer and the GaN layer. Smooth interfaces and an excellent coalescence of AlGaN on AlN and of GaN on the top of the MQW are reported. In addition the technique provides a powerful tool to manage the strain of the structure and to reduce the resulting curvature of the wafer.

Magnetic properties of InMnAs nanodots prepared by MOVPE

Ferromagnetic properties of self assembled In1−xMnxAs nanodots prepared by low pressure metalorganic vapor phase epitaxy were studied. Nanodot structures were grown on (100) GaAs substrates at the temperature of 500°C and reactor pressure of 100mbar. Magnetization measurements indicated that up to MnAs molar fraction of x∼0.143, nanodot structures presented typical properties of diluted magnetic semiconductors, i.e. Curie temperature depends on the Mn content in the alloy. Above this molar fraction, the Curie temperature becomes constant at the value of 353K. Electron diffraction patterns showed presence of two zinc-blende structures with different lattice constants. We suppose that zinc-blende MnAs is responsible for this behavior. No presence of NiAs structure that is typical for common hexagonal MnAs was observed.

AP-MOVPE GaInSb: Influence of V/III ratio on quality and indium incorporation

The growth of atmospheric pressure metal-organic vapour phase epitaxial (AP-MOVPE) GaSb and Ga1−xInxSb layers with different nominal V/III ratios (1.0–2.0) at 550°C, using trimethylantimony (TMSb), trimethylindium (TMIn) and triethylgallium (TEGa), is being reported. Ga1−xInxSb layers were grown with a constant indium mole fraction in the vapour phase (xv) in order to study the dependence of the indium mole fraction in the solid (x) on the V/III ratio. The surface morphology, crystallinity and optical properties of these layers are compared to those of GaSb layers with the aim of understanding their level of sensitivity to changes in the V/III ratio. It has been observed that the indium incorporation into GaSb increases with an increase in the V/III ratio. The shift of the free exciton/band-to-band transition in Ga0.96In0.04Sb with temperature follows the Varshni relation: E(T)=0.777–7.559×10−4T2/(720+T) .

On the electrical properties of Si-doped InGaP layers grown by low pressure‐metalorganic vapor phase epitaxy

The electrical properties of undoped and silicon doped InGaP layers grown lattice matched on GaAs by low pressure metal–organic vapor phase epitaxy were investigated under different growth conditions. The possible presence of superlattice ordering was excluded by photoluminescence analysis. Undoped layers exhibited a background p-type contamination of the order of 1016cm−3; the role of possible carbon contamination is discussed. Capacitance–voltage and Hall investigation of Si-doped n-type layers evidenced a room temperature free electron density linearly increasing from 3.6×1016 to 6×1018cm−3 as a function of the Si precursor flow. The corresponding electron mobilities decreased from 1800 to 483cm2/Vs. At lower temperatures, the conductivity and mobility of the n-doped samples showed a metallic like behavior, in some cases with values not consistent with a simple electronic transport into the conduction band, suggesting the presence of an additional parallel transport channel. Five main electron traps were identified by deep level transient spectroscopy and among them, two traps resulted to be dominant, one turned out to play a major role in the bulk, probably associated to the Si doping, and the other was active near the InGaP surface, ascribable to P-related defects.

Characterization of InMnSb epitaxial films for spintronics

Dilute (III, Mn)V ferromagnetic magnetic semiconductors have potential applications in spintronic devices as magnetic field sensors, spin transistors and reconfigurable logic devices. For such applications ferromagnetism at room temperature is a practical requirement. Previous work has shown that In1−xMnxSb films grown on GaAs (100) substrates by atmospheric pressure metalorganic vapour phase epitaxy were single phase and had high temperature ferromagnetism for Mn concentrations up to 2%. Here we present a study of InMnSb thin films at higher Mn concentration (10 at%) showing ferromagnetic properties at room temperature. Aberration corrected and analytical (scanning) transmission electron microscopy techniques were used to study the structure and elemental distribution of the In1−xMnxSb/GaAs system. The crystalline quality of the film and the presence of phase separation is evaluated in the context of a cluster-mediated ferromagnetism model.

High Quality GaAs Nanowires Grown on Glass Substrates

We report for the first time the growth of GaAs nanowires directly on low-cost glass substrates using atmospheric pressure metal organic vapor phase epitaxy via a vapor-liquid-solid mechanism with gold as catalyst. Substrates used in this work were of float glass type typically seen in household window glasses. Growth of GaAs nanowires on glass were investigated for growth temperatures between 410 and 580 °C. Perfectly cylindrical nontapered nanowires with a growth rate of ~33 nm/s were observed at growth temperatures of 450 and 470 °C, whereas highly tapered pillar-like wires were observed at 580 °C. Nanowires grew horizontally on the glass surface at 410 °C with a tendency to grow in vertically from the substrate as the growth temperature was increased. X-ray diffraction and transmission electron microscopy revealed that the nanowires have a perfect zinc blende structure with no planar structural defects or stacking faults. Strong photoluminescence emission was observed both at low temperature and room temperature indicating a high optical quality of GaAs nanowires. Growth comparison on impurity free fused silica substrate suggests unintentional doping of the nanowires from the glass substrate.

High resolution X-ray diffraction study of InAs layers grown with and without bismuth flow on GaAs substrates by metalorganic vapor phase epitaxy

InAs layers were grown with and without bismuth flow by atmospheric pressure metalorganic vapor phase epitaxy on exactly oriented, 2° and 10° misoriented (100) GaAs substrates. Structural analysis was carried out using high resolution X-ray diffraction. Without bismuth flow, only InAs layers grown on 10° misoriented substrates exhibit a mosaic structure. Layers grown on exactly oriented and 2° misoriented substrates show large full widths at half maxima of their diffraction rocking curves. Growing InAs under bismuth flow leads to the reduction of this full width indicating a clear improvement of their structural quality. Particularly for samples grown on 10° misoriented substrates, a complete disappearance of the mosaic structure was obtained. The crystalline quality improvement is attributed to the contribution of Bi nanodots in relieving strain.

The effect of ammonia flow in the AlN spacer on the electrical properties of InAlN/AlN/GaN HEMT structures

AbstractDuring the past few years it has been reported that a thin AlN spacer of few nanometers needs to be inserted in InAlN/GaN high electron mobility transistors (HEMTs) to obtain high 2DEG carrier mobility. This work presents a systematic study of the effects of varying the ammonia flow in the AlN spacer of InAlN/AlN/GaN HEMTs grown by low pressure metalorganic vapour phase epitaxy (LP‐MOVPE). The strain state, the surface roughness and the growth rate of AlN were found to be dependent on the V/III ratio. In addition the ammonia flow in the interlayer has a strong impact on the structural properties of the subsequent InAlN barrier layer and on the electrical properties of the structure. A sheet resistance as low as 327 Ω/□ with a sheet carrier density of 1.5 × 1013 cm−2 has been obtained at room temperature.

MOVPE growth of AIIIBV‐N semiconductor compounds for photovoltaic applications

AbstractThe present work presents the influence of the growth parameters on the structural and optical properties of undoped GaAsN epilayers and triple quantum wells 3×InGaAsN/GaAs obtained by atmospheric pressure metal organic vapour phase epitaxy APMOVPE. The structures were examined using high resolution X‐Ray diffraction HRXRD, contactless electroreflectance CER, photocurrent PC and Raman RS spectroscopies. The influence of the growth temperature and the gas phase composition on the material quality and alloy composition of the investigated structures as well as the growth and calibration characteristics are presented and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of local density of electron states in InGaAs/GaAs quantum rings by combined STM/AFM

The electronic structure of self-assembled InGaAs/GaAs(001) quantum rings grown by atmospheric pressure metal-organic vapor phase epitaxy has been investigated by combined scanning tunneling/atomic force microscopy (STM/AFM) in ultrahigh vacuum (UHV) for the first time. The current images and the tunnel spectra of contact of Pt-coated Si AFM probe to the quantum ring heterostructure surface revealing the spatial distribution of the local density of states and the electron size quantization spectra in the quantum rings have been obtained.