Pressure MOVPE Research Articles

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).

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.

Influence of GaN template thickness and morphology on AlxGa1−xN luminescence properties

We report on AlxGa1−xN/GaN films grown by atmospheric pressure MOVPE in a home-made vertical reactor. The high temperature GaN template is grown using the Si/N treatment of (0001) sapphire substrate. This process presents advantages of ELO technology without its ex-situ complicated steps and induces 3D (initial stage) to 2D growth mode. We investigate systematically the effect of the template thickness and morphology on optical properties of the AlGaN films by photoluminescence (PL) measurements. Four 0.5μm-thick Al0.07Ga0.93N samples on different GaN templates have been studied. PL spectra, dominated at low temperature by the donor bound exciton emission line, show a better film quality when AlGaN is grown on 1.3μm-thick high quality 2D GaN template. Two quenching mechanisms of the donor bound exciton PL-intensity are discussed. The PL peak linewidth increases as a function of Al composition. A bowing parameter of 0.93eV is obtained from the band gap variations as a function of Al composition.

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).

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.

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.

Characterization of low Al content AlxGa1−xN epitaxial films grown by atmospheric‐pressure MOVPE

AbstractAlxGa1−xN epitaxial films grown on GaN/sapphire by atmospheric‐pressure metalorganic vapor phase epitaxy (AP‐MOVPE) using trimethylgallium (TMG) and trimethylaluminum (TMA) as group III precursors have been studied. Two groups of samples were grown. The aluminum (Al) solid composition of AlxGa1−xN was varied in the range from 0.03 to 0.20 by changing the molar flow ratio [TMA/(TMA + TMG)]. The effect of TMA flow rate, respectively, TMG flow rate, on the growth rate, and Al solid composition is discussed. The structural properties of the alloys have been investigated by high‐resolution X‐ray diffraction (HRXRD). The optical properties of these samples were investigated by photoluminescence (PL). It is found that on increasing Al solid composition, via an increase of the TMA flow rate, the structural quality is deteriorated and the growth efficiency decreases. On the other hand, when the TMG flow rate is reduced, a decrease of the full width at half‐maximum (FWHM) is observed with Al content.

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.

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.

Effect of AlInGaN barrier layers with various TMGa flows on optoelectronic characteristics of near UV light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy

Near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barriers (QBs) are grown by atmospheric pressure metalorganic vapor phase epitaxy. The indium mole fraction of AlInGaN QB could be enhanced as we increased the TMG flow rate. Both the wavelength shift in EL spectra and forward voltage at 20 mA current injection were reduced by using AlInGaN QB. Under 100 mA current injection, the LED output power with Al 0.089In 0.035Ga 0.876N QB can be enhanced by 15.9%, compared to LED with GaN QB. It should be attributed to a reduction of lattice mismatch induced polarization mismatch in the active layer.

Magnetism in GaN layers implanted by La, Gd, Dy and Lu

We present a complex study of rare earth elements implanted GaN layers grown by low pressure metal-organic vapor phase epitaxy on c-plane sapphire substrates. Gd, Dy, La and Lu ions were implanted with energies of 200 keV and doses ranging from 5 × 10 13 to 4 × 10 17 atoms.cm − 2 . The chemical composition and concentration profiles of ion-implanted layers were studied by secondary ion mass spectrometry and Rutherford back scattering. The structural properties of the layers were characterized by Rutherford back scattering/channeling and X-ray diffraction reciprocal space mapping. Gd implanted layers exhibit ferromagnetic behavior persisting up to ~ 720 K. Since the ferromagnetic behavior was not observed in the case of La and Lu implanted layers, it cannot be attributed to the structural damage of the layer. Based on the fact that the samples are electrically conducting we conclude that the ferromagnetism can be associated with doped electrons mediating the ferromagnetic interaction between local moments on Gd and Dy.

The effect of trimethylgallium flows in the AlInGaN barrier on optoelectronic characteristics of near ultraviolet light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy

The letter reports a theoretical and experimental study on the device performance of near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barrier (QB). The indium mole fraction of AlInGaN QB could be enhanced as we increased the trimethylgallium flow rate. It was found the AlInGaN/InGaN LEDs can reduce forward voltage and improve light output power, compared with conventional GaN QB. By using advanced device simulation, it should be attributed to a reduction in lattice mismatch induced polarization mismatch in the active layer, which results in the suppression of electron overflow.

Reactor dependent starting transients of doping profiles in MOVPE grown GaN

The quality of heterostructures greatly depends on the accurate placement of dopants. However, doping transients remain as drawback in vapor-phase epitaxy. In this work starting transients of doping profiles of Si and Mg in GaN layers grown by low pressure metal-organic vapor-phase epitaxy (MOVPE) on sapphire have been investigated. Here we restrict the investigation to concentrations typically used for electrical or electro-optical devices which are in the range of 2×10 17 cm −3 to 1×10 19 cm −3 for Si and 3×10 19 cm −3 to 1×10 20 cm −3 for Mg. In the case of Mg possible diffusion was excluded by growing the doped layers at a lower growth temperature, far too low for device structures, where the profiles show essentially no sign of Mg back-diffusion. In the case of lower Si concentrations we did not observe diffusion at usual growth temperatures. The profiles were measured by secondary ion mass spectrometry. By comparing the transients from two different reactor types we show and quantitatively explain the influence of adsorption at the internal surfaces of the reactor on the dopant incorporation.

Effect of gas flow rate on surface morphology and crystal quality of ZnTe epilayers grown on GaAs substrates

Abstract The effect of gas flow rate on surface morphology and crystal quality of ZnTe layers grown on the (1 0 0) GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy with dimethylzinc and diethyltelluride as the source materials was investigated. The surface morphology of the ZnTe epilayers is significantly improved with increasing the total gas flow rate. X-ray rocking curve and photoluminescence measurements indicate that the total gas flow rate plays a vital role in the growth characteristics of the ZnTe epilayers, and the ZnTe epilayer with best crystal quality is obtained at the total gas flow rate around 300 standard cubic centimeters per minute (sccm) in this work.

Selective MOVPE growth of InAs QDs using double-cap procedure

Broadband spectrum emission was obtained for self-assembled Stranski–Krastanov (S–K) InAs/InP quantum dots (QDs) grown by selective area low pressure metalorganic vapor phase epitaxy (MOVPE) using the double-cap procedure. Selective area growth using a SiO2 narrow stripe mask array pattern was carried out to control and widen the emission wavelength range of the QDs in 16 stripe mask array waveguides. The height of the QDs in the multi stacked QD layers was changed using the double-cap procedure, and the strain was controlled by changing the composition of the GaInAs buffer layer under the QDs, which resulted in the broadband spectrum emission of this structure.

Effect of growth pressure on coalescence thickness and crystal quality of GaN deposited on 4H–SiC

The influence of growth pressure on the coalescence thickness and the crystal quality of GaN deposited on 4H–SiC by low pressure metalorganic vapor phase epitaxy was studied. It was shown that growth pressure has an impact on the surface roughness of epilayers and their crystal quality. GaN coalescence thicknesses were determined for the investigated growth pressures. The GaN layers were characterized by AFM and HRXRD measurements. HEMT structures were also fabricated and characterized. Among the growth pressures studied, 50, 125 and 200 mbar, 200 mbar was found to be most suitable for GaN/SiC epitaxy.