Pressure Metalorganic Vapor Phase Research Articles

Atmospheric-pressure metalorganic vapour phase epitaxy optimization of GaAsBi alloy

Metalorganic vapour phase epitaxial growth of GaAsBi alloy has been carried out at atmospheric pressure in horizontal geometry reactor. In order to achieve the growth of this alloy, we have investigated the growth conditions which allow epitaxial layers of a good crystalline quality with a maximum bismuth concentration. Growth parameters such as growth temperature, trimethylbismuth (TMBi) flow and V/III ratio were checked on a wide range. Growth temperature was varied between 365 and 450 °C, TMBi flow was checked in the range below 2 µmol/min and V/III ratio was varied between 6 and 20. According to our experimental results based on in-situ reflectivity measurements, scanning electron microscopy observations and high resolution X-ray diffraction analysis, it was found that the maximum Bi concentration reached in GaAs 1 − x Bi x layers was 3.7%. This maximum, relative to atmospheric-pressure metalorganic vapour phase epitaxy technique, was found under a growth temperature of 420 °C, a TMBi flow of 0.2 µmol/min and a V/III ratio of 9.5.

Growth of undoped ZnMgTe layers by metalorganic vapour phase epitaxy

The ternary undoped Zn1-xMgxTe layers have been grown on (100) ZnTe substrates by atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) using dimethylzinc (DMZn), bis-methylcyclopentadienyl-magnesium ((MeCp)2Mg) and diethyltelluride (DETe). The effects of the transport rates of DMZn and (MeCp)2Mg upon the Mg composition the low temperature photoluminescence (PL) property of Zn1-xMgxTe layer have been investigated. The PL spectra exhibit two distinctive luminescence bands, i.e. excitonic emission (band A) and donor-acceptor pair recombination emission (band B). The intensity ratio of the peak A to peak B increases with decreasing DMZn transport rate, indicating that the optical property of the layer is improved. The control of the Mg composition by (MeCp)2Mg transport rate under VI/II ratios of one to two has an advantage in achieving both the controllability of Mg composition and good optical property of undoped Zn1-xMgxTe layer grown by atmospheric pressure MOVPE.

Optimization of GaN Barriers During the Growth of InGaN/GaN Quantum Wells at Low Temperature

AbstractInGaN/GaN MQWs are grown on c-plane sapphire substrates using a low pressure metal organic vapor phase epitaxy (MOVPE) system. Trimethylgallium (TMGa), Triethylgallium (TEGa), Trimethylindium (TMIn) and ammonia were used as precursors for Ga, In and N, respectively and the growths were carried out at low temperature. Structural properties of grown MQWs are characterized using atomic force microscopy (AFM), and scanning electron microscope (SEM) and x-ray diffraction technique (XRD) is used to calculate the Indium incorporation in these MQWs. Surface morphologies over large areas of InGaN/GaN MQWs are observed using the tapping mode AFM; results indicate the surface roughness depends on the barrier thickness. Density of V- defects, effect of barrier width on the surface morphology and also on V-defect density will be presented and discussed.

Ion beam studies of InAs/GaAs self assembled quantum dots

Self assembled InAs/GaAs quantum dots (QD’s) emit in the wavelength range (1.3–1.55μm) revealing an enormous potential to become the active elements of low threshold lasers and light emitting diodes for communication systems. However, the luminescence is dramatically quenched at room temperature (and even below) due to the defects in the GaAs matrix which open non-radiative recombination paths.In this study we combine Rutherford backscattering/channelling (RBS-C) and high resolution X-ray diffraction (HRXRD) to study the structural properties of the InAs/GaAs structures. The InAs/GaAs QD heterostructures were grown by atmospheric pressure metal organic vapour phase epitaxy. Channelling measurements reveal a good crystalline quality along the main axial directions with minimum yields in the range of 4–6% through the entire capping layer. An increase on the dechannelling rate was observed in the region where the InAs quantum dots were buried. The channelling results also give evidence for the presence of defects preferentially oriented. Detailed angular scans in a structure with a 28nm cap allowed the study of the In orientation with respect to the GaAs matrix and a perfect alignment was found along the growth direction. The strain in the dots shifts the angular curves along the tilt directions.

Technology and characterisation of GaAsN/GaAs heterostructures for photodetector applications

AbstractThe nitrogen-containing conventional AIIIBV semiconductor alloys, so-called diluted nitrides (AIIIBV-N), have been extensively studied recently. Unusual properties of these materials make them very promising for applications in lasers and very efficient multijunction solar cells. This work presents the technology and properties of undoped GaAs1-xNx/GaAs heterostructures used as active regions in the construction of metal-semiconductor-metal (MSM) photodetectors. The atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) was applied for growing MSM test structures. Their structural and optical properties were examined using high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and photoreflectance spectroscopy (PR). Chemical wet etching was applied for forming an active region and a multifinger Schottky metallization was used as MSM contacts. Dark and illuminated current-voltage characteristics were measured. Based on the obtained results, the main detector parameters as responsivity and spectral response were estimated

White light-emitting diodes based on a single InGaN emission layer

White light-emitting InGaN∕GaN diode with an InGaN underlying layer grown on the (0001) sapphire substrate was fabricated by low pressure metal-organic vapor phase epitaxy. The electroluminescence measurements show that the emitted white light is composed of blue and yellow lights, centered at around 440 and 570nm, respectively, for an injection current of 20mA. Cross-sectional transmission electron microscopy reveals that In-rich quantum dots were formed in InGaN wells due to phase separation of indium. It is suggested that the yellow and blue lights come from In-rich quantum dots and the low-indium regions, respectively, in InGaN quantum wells.

New approach of Nano-Selective Area Growth (NSAG) for a precise control of GaN nanodots grown by MOVPE

Nanodots arrays of GaN have been successfully grown on GaN template substrates using nano-selective area growth (NSAG). The substrates used in NSAG were partially covered by dielectric masks in which nano-apertures have been patterned by electron-beam nanolithography and reactive ion etching. The growths were performed by low pressure metal organic vapour phase epitaxy (MOVPE) using 100% N 2 as carrier gas. TMGa and NH 3 were used as sources of gallium and nitrogen, respectively. The layers were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Perfect selectivity of GaN on the masked substrate has been obtained. The nanodots grown in the nano-apertures are well shaped and homogenous with smooth surface side walls.

Photoinduced current transient spectroscopy of deep levels and transport mechanisms in iron-doped GaN thin films grown by low pressure-metalorganic vapor phase epitaxy

Electrical transport and deep levels are investigated in GaN:Fe layers epitaxially grown on sapphire by low pressure metalorganic vapor phase epitaxy. Photoinduced current transient spectroscopy and current detected deep level spectroscopy are performed between 200 and 650 K on three Fe-doped samples and an undoped sample. A detailed study of the detected deep levels assigns dominant centers to a deep donor 1.39 eV below the conduction band edge EC and to a deep acceptor 0.75 eV above the valence band edge EV at low electric field. A strong Poole–Frenkel effect is evidenced for the donor. Schottky diodes characteristics and transport properties in the bulk GaN:Fe layer containing a homogenous concentration of 1019 Fe∕cm3 are typical of a compensated semiconductor. They both indicate that the bulk Fermi level is located typically 1.4 eV below EC, in agreement with the neutrality equation and dominance of the deep donor concentration. This set of results demonstrates unambiguously that electrical transport in GaN:Fe is governed by both types, either donor or acceptor, of the iron impurity, either substitutional in gallium sites or associated with other defects.

APMOVPE growth and characterisation of undoped GaAsN/GaAs heterostructures

Unusual properties of the diluted nitrides A IIIB V–N make them very attractive in the point of view of fundamental investigations and practical applications. This work presents the growth characteristics and properties of the undoped GaAs 1− x N x /GaAs heterostructures obtained by the atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). The properties of the heterostructures were examined using high-resolution X-ray diffraction (HRXRD), photoreflectance spectroscopy (PR), photoluminescence (PL), photovoltage spectroscopy (PVS) and mercury probe C– V set-up with an HP 4192A impedance analyser (5 Hz–13 MHz). The maximum nitrogen content in GaAs 1− x N x epilayers, determined from PR spectra, did not exceed 1.74%. The influence of the growth temperature ( T g) and the nitrogen source concentration in gas phase ( X g) on the properties of the GaAs 1− x N x /GaAs heterostructures is presented and discussed.

The surface diffusion of Ga species on an AlGaN facet structure in low pressure MOVPE

The diffusion of Ga species in gas phase as well as on the surface are studied in selective area growth of AlGaN in low pressure metalorganic vapor phase epitaxy. The experiments were performed on a trapezoidal stripe with (0001) facet on the top and (1-101) facet on the sides. It was found that the ridge growth on the facets were sensitive to the growth pressure, in agreement with numerical results. At a low pressure of 100 Torr, we got a uniform thickness of AlGaN alloy, but the alloy composition was not uniform. Exponential variation of the composition gave the effective diffusion length of Ga on the order of 0.7 μm which was independent of the growth pressure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth characteristics of ZnMgTe layer on ZnTe substrate by metalorganic vapor phase epitaxy

The ternary Zn 1− x Mg x Te epitaxial layers have been successfully grown on (1 0 0) ZnTe substrates by atmospheric pressure metalorganic vapor phase epitaxy using dimethylzinc, bis-methylcyclopentadienyl-magnesium ((MeCp) 2Mg) and diethyltelluride (DETe) as source materials. The effects of source transport rates and total gas flow rate upon the Mg composition in the Zn 1− x Mg x Te layers have been investigated. It was found that the Mg composition drastically increase with decreasing DETe transport rate or with increasing the total gas flow rate, which may be associated with the reduction of the premature reaction between DETe and (MeCp) 2Mg.

Analysis of GaN decomposition in an atmospheric MOVPE vertical reactor

The GaN decomposition versus the annealing ambient (H2, N2 + H2) have been investigated in atmospheric pressure metal organic vapor phase epitaxy (AP-MOVPE) vertical reactor. A comparison between the low temperature GaN (LT-GaN) decomposition in a vertical reactor and a horizontal one was discussed in order to explain the failure of high temperature GaN (HT-GaN) growth on Al2O3 using 2D buffer layer under a mixture of H2 and N2 in our vertical reactor. Decomposition rates versus temperature and ambient gas were measured using real time laser reflectometry. The surfaces of these films were analyzed using a scanning electron microscopy (SEM). Hydrogen seems to considerably affect the LT-GaN surface morphology by a mass transport, diffusion on the substrate surface and by a decomposition process even in the presence of ammonia and nitrogen. The high decomposition rates of the LT-GaN measured in comparison to that determined for the HT-GaN one is attributed to the amorphous-like structure of the layer and the instability of Ga-N bonds. This favors the appearance of a mirror-like gallium surface in the beginning of this layer decomposition. The presence of liquid gallium catalyzes the decomposition process. HT-GaN SEM analysis revealed that the surface of the “totally” decomposed GaN surface is dominated by gallium droplets. These were removed. The region around and under these droplets is capped by a porous like GaN film. The coalesced gallium droplets may cover some areas of partially decomposed GaN and preserve them from H2 attack and total decomposition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

BGaN materials on GaN/sapphire substrate by MOVPE using N 2 carrier gas

BGaN materials with good structural quality and surface morphology have been successfully grown on GaN template substrates by low pressure metal organic vapour phase epitaxy. TEB and NH3 were used as precursors of boron and nitrogen, respectively. All the growths were performed under 100% N 2 process gas. Boron concentration was estimated by HRXD measurements combined with SIMS analysis. Single-crystal layers BGaN with B content as high as 3.6% have been obtained.

1.3 µm emission from InAs/GaAs quantum dots

AbstractWe report here the results of our photoluminescence study of a series of single quantum dot layer structures containing InxGa1–xAs strain reducing layers with different In concentration (from 0% to 29%), prepared by low pressure metal organic vapour phase epitaxy. These structures display a strong red shift of photoluminescence maxima from 1.25 μm to 1.45 μm at 300 K with increased In content in the ternary layer. The origin of the observed transitions has been explained using magnetophotoluminescence measurements and photoluminescence measurements for different pumping intensities at low temperature. Optical transition energies were calculated using a simple single‐band effective mass model with energy‐dependent effective mass. Comparing the calculated and measured energies, we can determine the thickness of the wetting layer and the sizes of the dots. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of dopant transport rate upon photoluminescence and electrical properties of ZnTe in atmospheric pressure MOVPE using tris-dimethylaminophosphorus

The P-doped ZnTe layers have been grown on ZnTe (1 0 0) substrates by atmospheric pressure metalorganic vapor phase epitaxy using tris-dimethylaminophosphorus (TDMAP). The effects of dopant transport rate upon the photoluminescence and electrical properties of ZnTe layers have been investigated. ZnTe layer with a carrier concentration of 1.3×10 18 cm −3 is obtained by using this dopant source. Most ZnTe epitaxial layers exhibit strong band-edge emission at room temperature. It is expected that TDMAP is a useful dopant source, compared to tertiary-butylphosphine.

MOVPE growth study of BxGa(1−x)N on GaN template substrate

BGaN materials with good structural quality and surface morphology have been successfully grown on GaN template substrates by low pressure metal organic vapour phase epitaxy . TEB and NH3 were used as precursors of boron and nitrogen respectively. All the growths were performed under 100% N 2 process gas. Boron concentration was estimated by HRXD measurements combined with SIMS analysis. Single-crystal layers of BGaN with B content as high as 3.6% have been obtained.

Laser reflectometry in situ monitoring of InGaAs grown by atmospheric pressure metalorganic vapour phase epitaxy

InGaAs layers on undoped GaAs (0 0 1) substrates were grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE). In order to obtain films with different indium composition ( x In), the growth temperature as a growth parameter, was varied from 420 to 680 °C. Furthermore, high-resolution X-ray diffraction (HRXRD) measurements were used to quantify the change of x In. Crystal quality has been also studied as a function of growth conditions. On the other hand, laser reflectometry (LR) at 632.8 nm wavelength, was employed to in situ monitor epitaxy. Reflectivity–time signal was enabled to evaluate structural and optical properties of samples. We have fitted experimental data to determine optical constants and growth rate of InGaAs at 632.8 nm. In addition, the fitting provided InGaAs thickness as a function of growth time. Based on ex situ characterization by scanning electronic microscopy (SEM) and HRXRD, we propose a practical method, relating the contrast of first reflectivity maximum with the X-ray diffraction peak angular difference between the substrate and epitaxial layer, to determine in situ the In solid composition in InGaAs alloys.

MOVPE growth of InAs quantum dots for mid-IR applications

InAs quantum dots (QDs) grown on In x Ga 1- x As/InP matrix by low pressure metal organic vapor phase epitaxy (LP-MOVPE) in nitrogen ambient were studied. Formation of the InAs QDs with different growth conditions was investigated. To improve the dot size uniformity, a two-step growth method was used and investigated. It is found that morphology of the InAs QDs formed on such In x Ga 1- x As/InP matrix is very sensitive to the growth conditions. InAs QDs with high density of 1.3 × 10 10 cm −2 are grown by using S-K growth method with fast growth rate. Using the two-step growth method, the InAs QDs size uniformity improves by 63% and 110% compared that of the dots grown by ordinary S-K method and ALE method, respectively. Narrow photoluminescence (PL) emission spectrum of the QDs grown by using the two-step growth method, is received. FWHM of the PL curve is measured at 26 meV and the peak emission wavelength is larger than 2.3 μm at 77 K.

High temperature refractive indices of GaN

AbstractUndoped GaN (u‐GaN) films were grown by low pressure metalorganic vapour phase epitaxy (LP‐MOVPE) on sapphire substrates. In situ optical monitoring was applied to the growth process either using a LayTec EpiR‐DA TT spectroscopic reflectometer or Filmetrics F30. Refractive indices of u‐GaN films at 1060 °C were obtained in a spectral range from 370‐900 nm. A peak at 412±5 nm in refractive index spectra was observed, which most likely corresponds to the band‐gap of hexagonal GaN at a temperature of 1060 °C. Refractive indices below this band‐gap are fitted well to the first‐order Sellmeier formula. As an example of the applications of the refractive indices, the effective film thicknesses of GaN during the resumption from 3 dimensional (3D) to 2 dimensional (2D) growth have been calculated from the spectra recorded by a LayTec system using the optical constants obtained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Strain and microstructure in Fe‐doped GaN layers grown by low pressure metalorganic vapour phase epitaxy

AbstractIn order to get semi‐insulating GaN layers with a low dislocation density on sapphire, two kinds of Fe doping were explored by low pressure metalorganic vapour phase epitaxy (LP‐MOVPE): the modulation doping (MD) and the continuous doping (CD). The high crystalline quality and the semi‐insulating character are obtained in the case of the Fe‐MD layers. The effect of Fe doping on the strain was investigated in both kind of layers (MD and CD) by X‐ray diffraction, photoluminescence and reflectivity. The lattice parameters are functions of the iron doping level, whatever the doping mode. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)