Pressure MOVPE Research Articles

Surfactant effect of bismuth in atmospheric pressure MOVPE growth of InAs layers on (1 0 0) GaAs substrates

InAs layers have been grown on GaAs substrates with and without bismuth flow, at a growth temperature of 450 °C and a V/III ratio of 18, by atmospheric pressure metal–organic vapor phase epitaxy. Thickness measurements using scanning electron microscopy show that bismuth reduces the growth rate. Atomic force microscopy images show the presence of Bi islands inlayed in InAs layer degrading its surface morphology. High resolution X-ray diffraction curves confirm that bismuth does not incorporate into InAs layers but improves the crystalline quality by reducing the dislocation density. This improvement is attributed to Bi nanodots contributing to the strain relaxation. Room temperature Hall effect measurements have evidenced that growing InAs under Bi flow increases the electron mobility. Therefore Bi acts as a surfactant during growth of InAs layers on GaAs substrate.

Photoreflectance and photoluminescence study of annealing effects on GaAsBi layers grown by metalorganic vapor phase epitaxy

The optical properties of GaAsBi layers grown by atmospheric pressure metalorganic vapor phase epitaxy on p-type GaAs substrates and annealed at different temperatures are investigated by photoreflectance and photoluminescence spectroscopies. Photoreflectance spectra show no significant shift in the band gap energy of GaAs0.965Bi0.035 with annealing temperature except 600 °C for which the band gap energy reaches a minimum value corresponding to a red shift of 60 meV. The low temperature photoluminescence spectra of GaAsBi layers show a broad band centered at ∼1.36 eV. The temperature dependence of the 1.36 eV emission band in addition to the increasing intensity of this band with bismuth flow suggests that it is originated from Bi clusters or from complex defects probably located at the surface/interface of the GaAsBi epilayer.

Boron lattice site location in (BGa)As and (BGa)P thin films studied using RBS and NRA with a channeled He+ ion beam

Abstract In this study the boron lattice site location in ternary B x Ga 1− x As and B x Ga 1− x P thin films grown on (0 0 1) GaAs and (0 0 1) GaP, respectively, using low pressure metal-organic vapour-phase epitaxy (MOVPE) with boron concentrations between x = 0.8% and x = 3.2% was investigated with RBS and the 10 B(α,p) 13 C nuclear reaction using a 2.3 MeV He + ion beam. For this purpose, the ion beam was aligned with the [0 0 1], [0 1 1] and [1 1 1] axis and the RBS and proton yield from the nuclear reaction compared with random ion incidence. For comparison, theoretical proton yields which assume boron to be located on substitutional lattice sites only were calculated for each sample/axis combination and compared with the experimental yields. The RBS/channeling measurements show a very good crystal quality of the films with χ min being in the range of 3–5% for the [0 1 1] axis. The best crystal qualities, i.e. the lowest χ min values and dechanneling rates, are achieved for low boron concentrations. From NRA/channeling it can be deduced that in the B x Ga 1− x As films the fraction of interstitial boron is approximately 5% for low boron concentrations of x = 1% and 6–10% for concentrations up to x = 3.2%, whereas the fraction of interstitial boron is less than 3% in the B x Ga 1− x P film studied despite a concentration of x = 2.0%. This indicates that antisite effects of the boron incorporation are more likely in GaAs compared to GaP.

Modulation frequency dependence of the photoelectrical response of GaAs/InGaP superlattices

Photoelectrical measurements were taken on a nominally undoped-InGaP/GaAs superlattice, inserted between two p+ and n+ InGaP cladding layers. The sequence of InGaP/GaAs alternated layers forming the superlattice was grown lattice matched on n+-GaAs substrates through low pressure-metal organic vapor phase epitaxy, at growth conditions previously optimized for obtaining sharp interfaces and negligible ordering effects in the cation sublattice of the InGaP layers. A peculiar dependence of both the photocurrent and the photovoltaic signals on the modulation frequency of the exciting light beam was observed and then interpreted according to proper equivalent electrical circuits. The effects induced by an incomplete depletion of the nominally undoped superlattice region are analyzed in detail, and the analogies between photoelectrical investigation and admittance spectroscopy are pointed out.

Properties of InAs grown on misoriented GaAs substrates by atmospheric pressure metal–organic vapor phase epitaxy

InAs epilayers were grown by atmospheric pressure metal–organic vapor phase epitaxy on GaAs (1 0 0) exactly oriented substrates and misoriented by 2° and 10° toward [1 1 1]A. The layers had varying thicknesses and were deposited under the same growth conditions. Atomic force microscopy analysis show that surface morphology depends on surface misorientation and presents a low root mean square. High resolution X-ray diffraction analysis and Hall effect measurements were preformed to check the substrate misorientation effect on the crystalline quality and electrical properties respectively.

Structural, electrical and optical characterization of InGaN layers grown by MOVPE

We present a study on n-type ternary InGaN layers grown by atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) on GaN template/(0001) sapphire substrate. An investigation of the different growth conditions on n-type Inx Ga1 − x N (x = 0.06 − 0.135) alloys was done for a series of five samples. The structural, electrical and optical properties were characterized by high resolution x-ray diffraction (HRXRD), Hall effect and photoluminescence (PL). Experimental results showed that different growth conditions, namely substrate rotation (SR) and change of total H2 flow (THF), strongly affect the properties of InGaN layers. This case can be clearly observed from the analytical results. When the SR speed decreased, the HRXRD scan peak of the samples shifted along a higher angle. Therefore, increasing the SR speed changed important structural properties of InGaN alloys such as peak broadening, values of strain, lattice parameters and defects including tilt, twist and dislocation density. From PL results it is observed that the growth conditions can be changed to control the emission wavelength and it is possible to shift the emission wavelength towards the green. Hall effect measurement has shown that the resistivity of the samples changes dramatically when THF changes.

Spectroscopic ellipsometry study of GaAs1−xBix material grown on GaAs substrate by atmospheric pressure metal-organic vapor-phase epitaxy

The optical properties in terms of complex dielectric function of GaAs1−xBix alloys (0%≤x≤3.7%), grown by atmospheric pressure metal-organic vapor-phase epitaxy, are determined by using room temperature spectroscopic ellipsometry. The interband transition energies in the energy range of 1.4–5.4 eV are resolved using a line shape fitting on the numerically calculated dielectric function second derivatives. The bismuth effect on the critical point parameters is then determined. We have found that, as for GaAs1−xBix alloys E0 transition, the bismuth incorporation shifts the E1, E1+Δ1, E2, and E0′ transition energies but with a lower magnitude. We also observed a root-square-like increase of the E1 broadening parameter (Γ1) with respect to the bismuth composition.

Heteroepitaxial growth of thin InAs layers on GaAs(1 0 0) misoriented substrates: A structural and morphological comparison

Thin InAs epilayers were grown on GaAs(1 0 0) substrates exactly oriented and misoriented toward [1 1 1]A direction by atmospheric pressure metalorganic vapor phase epitaxy. InAs growth was monitored by in situ spectral reflectivity. Structural quality of InAs layers were studied by using high-resolution X-ray diffraction. No crystallographic tilting of the layers with respect to any kind of these substrates was found for all thicknesses. This result is discussed in terms of In-rich growth environment. InAs layers grown on 2° misoriented substrate provide an improved crystalline quality. Surface roughness of InAs layers depend on layer thickness and substrate misorientation.

Structural Characterization of GaN Epitaxial Layers Grown on 4H-SiC Substrates with Different Off-Cut

The influence of surface preparation of 4H-SiC substrates on structural properties of GaN grown by low pressure metalorganic vapour phase epitaxy was studied. Substrate etching has an impact on the crystallographic structure of epilayers and improves its crystal quality. The GaN layers were characterized by RBS/channelling and HRXRD measurements. It was observed that on-axis 4H-SiC is most suitable for GaN epitaxy and that substrate etching improves the crystal quality of epilayer.

Effect of periodic interruption of the atmospheric-pressure MOVPE growth of InAs/GaAs quantum dots on their morphology and optoelectronic spectra

A modified regime of growing InAs/GaAs quantum dots (QDs) by metalorganic vapor phase epitaxy (MOVPE) at atmospheric pressure is described. In contrast to the standard growth regime, the time of periodic interruption of the supply of trimethylindium and arsin to the reactor was increased and varied from 4 to 18 s. It is shown that optimization of the interruption time leads to the formation of dense, homogeneous (with respect to dimensions) QD arrays and to a decrease in the concentration of coarse relaxed clusters without using additional treatments (e.g., doping with surfactants, chemical etching). In particular, the surface concentration of QDs increases up to 6 × 1010 cm−2, that is, by almost an order of magnitude as compared to the standard growth regime. QD structures grown using the modified MOVPE method are characterized by high thermal stability and ensure high intensity of room-temperature electroluminescence of the related edge-emitting Schottky diodes.

Effect of thermal annealing on structural and optical properties of the GaAs0.963Bi0.037 alloy

We have investigated the effect of thermal annealing on GaAs0.963Bi0.037 layers grown by atmospheric pressure metalorganic vapour phase epitaxy. High resolution x-ray diffraction (HRXRD) patterns show high crystalline quality and remarkable stability against thermal annealing up to 700 °C. When the annealing temperature reaches 750 °C, the GaAs0.963Bi0.037 alloy is no longer stable, and the HRXRD pattern reveals the presence of other peaks. Atomic force microscopy images show a surface accumulation of Bi islands which disappear at 750 °C. The photoluminescence (PL) is clearly improved after annealing, but no shift of the PL peak was observed. The optimal annealing temperature is found to be ∼700 °C.

Temperature effect study on structural and morphological properties of In .08Ga .92As/GaAs structures grown by MOVPE

In .08Ga .92As layers were grown on the GaAs(0 0 1) substrate by atmospheric pressure metalorganic vapour-phase epitaxy (AP-MOVPE). Among growth conditions, only growth temperature was varied in the range 520–680 °C. This temperature interval keeps solid indium composition constant when fixing vapour indium composition. In order to improve crystal quality and to contribute to the understanding of the growth kinetic, we have studied the temperature effect on morphological and structural properties and growth process of In .08Ga .92As/GaAs structures. Surface morphology evolution of InGaAs films (RMS surface roughness, hatchings and islands of formations, densities, sizes and uniformities, etc.) and growth process (growth anisotropy, etc.) versus growth temperature were investigated by atomic force microscopy (AFM) and plan-view scanning electronic microscopy (SEM). Dislocations density and alloys disorder (by using Urbach energy) changes of InGaAs alloys were examined by high-resolution X-ray diffraction (HRXRD) in rocking curves mode and optical absorption (OA) measurements, respectively. A correlation between results and comparison with the literature has been given. All measurements show that optimal growth temperature regarding crystal quality (defects density, alloys disorder, etc.) is about 520 °C. Besides, surface morphology of In .08Ga .92As at this temperature was specified by the presence of hatchings and the absence of islands. As a manufactured diffraction grating, we find that hatchings network can diffract a 632.8 nm incident laser.

Development and characterisation of improved ruthenium dopant sources

To form semi-insulating films capable of acting as current blocking layers and avoid intermixing of dopants and the consequent degradation of device properties the use of ruthenium (Ru) in indium phosphide (InP) has been studied. The conventional precursor bis(dimethylpentadienyl) ruthenium (DMRU) has significant limitations for atmospheric pressure-metal organic vapour phase epitaxy (AP-MOVPE) and to overcome the issues of low volatility, incorporation efficiency and stability under a hydrogen ambient a range of alternative Ru precursors were investigated, namely substituted cyclopentadienyl compounds of the general formula (RCp) 2Ru. In this work we report the physical properties of a more complete series of samples to establish the most suitable chemicals for deposition trials. The most promising precursors were identified as bis(isopropylcyclopentadienyl)ruthenium ((iPrCp) 2Ru) and bis(isobutylcyclopentadienyl)ruthenium ((iBuCp) 2Ru) due to their superior volatility and stability. These materials were also assessed as precursors for AP-MOVPE to establish their incorporation characteristics and usefulness for the target devices compared with the conventional DMRU source. The results demonstrate controlled Ru doping can be achieved using advanced source materials to provide access to novel device structures with enhanced performance capabilities.

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.

AP-MOVPE of InGaAs on GaAs (0 0 1): Analysis of in situ reflectivity response

We have investigated in situ monitoring of growth rate and refractive index by laser reflectometry during InGaAs on GaAs (001) substrate growth in atmospheric pressure metalorganic vapour-phase epitaxy (AP-MOVPE). The indium solid composition (xIns) was varied by changing the substrate temperature or the indium vapour composition (xInv). The refractive index of InGaAs alloys as a function of temperature and composition was quantified and compared which that of GaAs for 632.8nm wavelength by simulation of experimental reflectivity responses. Composition analyses were carried out by high-resolution X-ray diffraction (HRXRD) and optical absorption (OA). The layers thicknesses were estimated by scanning electron microscopy (SEM) observations. The temperature dependence of InGaAs growth rate has been investigated in the temperature range 420–680°C using trimethylgallium (TMGa), trimethylindium (TMIn) and arsine (AsH3) sources. It shows Arrhenius-type behaviour with an apparent activation energy Ea of 0.62eV (14.26kcal/mol). This value is close to that determinate in the AP-MOVPE of GaAs.

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.

SIMS depth profiling of Mg back-diffusion in (AlGaIn)N light-emitting diodes

The Mg doping profiles in close proximity to the (AlGaIn)N/GaN QW active region of group III-nitride light-emitting diodes grown by low pressure metal-organic vapor-phase epitaxy on sapphire substrates were investigated by secondary ion mass spectrometry (SIMS) depth profiling. The actual Mg profiles close to the active region have been found to be influenced by segregation as well as by back-diffusion during growth and can be controlled by appropriate growth temperatures. From the Mg depth profiles we estimated an activation energy of 4.5−4.7 eV for Mg diffusion in (AlGa)N.

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.

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.