Low-pressure Vapor Phase Epitaxy Research Articles

Influence of sapphire substrate with miscut angles on hexagonal boron nitride films grown by halide vapor phase epitaxy

(002) hexagonal boron nitride (h-BN) micron films were epitaxially grown on c-plane sapphire substrates with miscut angles to m-plane (m-miscut angle) by high-temperature and low-pressure halide vapor phase epitaxy.

Hexagonal boron nitride film on sapphire substrate grown by low-pressure and high-temperature halide vapor phase epitaxy

(002) hexagonal boron nitride (h-BN) films are epitaxially grown on c-plane sapphire substrates by low-pressure and high-temperature halide vapor phase epitaxy, using boron trichloride and ammonia as the boron source and nitrogen source. The influence of the gas phase composition has been investigated to improve the crystalline quality. For the deposition at a temperature of 1650 °C, the optimal nitrogen to boron ratio is identified as 6 and the corresponding deposition rate is around 26 nm/min. Under this condition, the c-lattice parameter of the h-BN layer is 6.66 Å. The h-BN film exhibits high transmittance larger than 70% in the visible range and its optical bandgap is determined to be 5.2 eV.

On the Influence of Pulsed Gamma-Neutron Irradiation on the Morphology of Self-Assembled GeSi/Si(001) Nanoislands

The influence of pulsed gamma-neutron irradiation on the surface morphology of GeSi/Si(001) heterostructures with surface self-assembled GeSi nanoislands grown by the combined sublimation molecular-beam epitaxy of Si and the low-pressure vapor-phase epitaxy of Ge is experimentally studied. Gamma-neutron irradiation is found to cause a change in the shapes of self-assembled GeSi nanoislands, in particular, a reduction in the aspect ratio of the nanoislands. The effect is related to elastic-strain relaxation in the GeSi nanoislands under their exposure to elastic waves generated in the course of gamma-neutron irradiation.

Fabrication of star-shaped InP/GaInAs core-multishell nanowires by self-catalytic VLS mode

We successfully fabricated core-multishell nanowires using low-pressure metal organic vapor phase epitaxy (MOVPE) in self-catalytic vapor-liquid-solid (VLS) mode. The central core consists of an InP nanowire, and the shells are composed of alternating InP and GaInAs layers. The dependence of the shape and optical characteristics of the nanowires on the number of InP/GaInAs periods were investigated. By increasing the shell-periods, we observed a star-shaped cross section. The optical characteristics of the nanowires were investigated by room-temperature photoluminescence (PL) spectroscopy. The number of PL peaks was found to increase with increasing number of periods, and the peaks became redshifted.

A low cost and single source atmospheric pressure vapor phase epitaxy of ZnS for thin film photovoltaic applications

A novel and low cost vapor phase epitaxy (VPE) method using a single non-volatile source has been used to deposit ZnS thin films on soda lime glass substrates. Utilization of the non-volatile source eliminates the need for expensive and sophisticated reactors commonly used in conventional VPE. Instead, this experiment was carried out using inexpensive and easily attainable apparatus. The vapor phase reaction process described is also more compatible to the industry standard dry deposition processes of the other layers in the thin film solar cell stack for Cu(In,Ga)Se2 (CIGS), Cu2ZnSnS4 (CZTS) and CdTe photovoltaic (PV) devices. In this experiment, the substrate temperature was varied from 400 to 480 °C and the ZnS thin films produced were analyzed using X-ray diffractometry (XRD), optical spectroscopy, field emission scanning electron microscope (FESEM) and Hall effect measurement system. The films were found to be hexagonal structured except for the film deposited at 480 °C, where the film was found to be cubic. The thickness, bandgap and resistivity of the deposited films ranged from 54 to 351 nm, 3.18 to 3.83 eV and 2 × 103 to 1.6 × 104 Ω·cm respectively.

Emission wavelength control of self-catalytic InP/GaInAs/InP core–multishell nanowire on InP substrate grown by metal organic vapor phase epitaxy

InP nanowires and InP/GaInAs/InP core–multishell nanowires were successfully grown on an InP(111)B substrate by low-pressure metal organic vapor phase epitaxy (MOVPE) using an indium catalyst. The self-catalytic vapor–liquid–solid (VLS) mode was used to obtain high-quality nanowires in which a deposited indium droplet acts as the catalyst instead of a metal particle, as in the case of the conventional VLS mode. InP core nanowire structures dependent on growth temperature and preheating temperature were obtained. InP/GaInAs/InP core–multishell nanowire structures, densities, and optical properties were investigated at various flow rates of trimethylindium (TMI) during the growth of InP core nanowires and the growth time of the GaInAs shell layer was also studied. The growth volume and density of nanowires were mainly dependent on growth temperature and preheating temperature, respectively. The height of nanowires was dependent on the TMI flow rate in the InP core nanowire growth, and the thickness of GaInAs shell layer was controlled by adjusting the growth time of the GaInAs shell layer. The photoluminescence (PL) intensity increased with increasing nanowire height and the peak wavelength was controlled by adjusting the thickness of the GaInAs shell layer.

Characterization of partially ordered GaInP/GaAs heterointerfaces by the quantum Hall effect

The new approach to the characterization of semiconductor interfacial properties by the quantum Hall effect (QHE) and the scanning near field optical microscopy (SNOM) is demonstrated to the heterointerfaces of partially ordered GaInP/GaAs grown by low-pressure Metal Organic Vapor Phase Epitaxy. The Shubnikov de-Haas (SdH) oscillations and the Hall plateaus are observed in the heterointerfaces of both the less-ordered and more-ordered GaInP/GaAs samples with a large clover-shape, but these samples exhibit both 2D and 3D electron behaviors. In contrast to large clover-shaped samples, the distinct SdH oscillations and the Hall plateaus in the less-ordered sample, while the single SdH oscillation and the corresponding large plateau in the more-ordered small Hall-bar sample are observed. These results suggest that there may be many domains, each having a different carrier density and sizes in the less-ordered sample, while one or few large domains with uniform carrier concentration and sizes in the more-ordered sample. In SNOM measurements, PL intensity varies in the mapping of the more-ordered sample and it is concluded that the variation of the PL intensity may result from an inhomogeneous distribution of non-radiative recombination centers in the more-ordered sample.

Dependence of Curie temperature on surface strain in InMnAs epitaxial structures

Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0 < x < 0.13) were prepared on GaAs substrates by low-pressure metal organic vapour phase epitaxy. Magnetic moment measurements indicated that reference epitaxial layer had a Curie temperature of 343 K independent on the composition. On the other hand, the quantum dots prepared under Stranski–Krastanov growth mode from the identical gas phase composition showed a lower value of Curie temperature. This value varied from 41 to 235 K in relation to the material composition. Moiré fringes at transmission electron microscopy plan view were used for characterization of strain in InMnAs quantum dot structures.

Optimization of the properties of MOVPE-grown GaP epitaxial layers on GaP (1 1 1)B substrates

Gallium phosphide (GaP) homoepitaxial layers are optimized by varying the growth temperature, growth rate and V/III ratio in a low-pressure metal organic vapour phase epitaxy (MOVPE) process. It is observed that we need high growth temperature, low growth rate and an optimum value of the V/III ratio in order to obtain a mirror finish surface morphology. The surface morphology is mirror finish for an epitaxial layer grown ⩾820 °C when viewed under a stereo-zoom microscope for a V/III ratio of about 100 or more. A sharp and intense excitonic photoluminescence (PL) feature and a fine structure associated with donor–acceptor pair recombination confirm a high optical quality of the grown layer, which is supported by high-resolution x-ray diffraction measurements. For silicon doping of GaP using silane in low-pressure MOVPE, our results confirm theoretical predictions available in the literature and the values of a distribution coefficient lie in a similar range known for other conventional semiconductors. This optimization provides high-quality GaP (1 1 1)B epilayers needed for the development of either nanostructure-based optoelectronic devices on transparent substrates or polarization-sensitive infrared photodetectors based on two-photon absorption.

Improvement of Crystal Quality of n-AlGaN by Alternate-Source-Feeding Metal Organic Vapor Phase Epitaxy

The crystal quality of AlGaN layers was improved using alternate-source-feeding epitaxy (ASFE) in low-pressure (LP) metal organic vapor phase epitaxy (MOVPE). The green emission of photoluminescence (PL) from the AlGaN clad layer was reduced, indicating that point defects such as Ga or Al vacancy were reduced by ASFE. On the other hand, the full width at half maximum (FWHM) of the X-ray rocking curve was not improved at all and the dislocation density observed by transmission electron microscopy (TEM) was not reduced by ASFE. Furthermore, the yellow emission from GaN/AlGaN multi-quantum well (MQW) grown by conventional-simultaneous source-feeding epitaxy (SSFE) on the ASFE AlGaN clad layer was also reduced. This indicates that the improvement of the crystal quality of the AlGaN clad layer influences the crystal quality of the MQW grown on it.

High-speed GaAs metal gate semiconductor field effect transistor structure grown on a composite Ge∕GexSi1−x∕Si substrate

In this study we used a low-pressure metal organic vapor phase epitaxy method to investigate the growth of GaAs metal gate semiconductor field effect transistor (MESFET) structures on a Si substrate. The buffer layer between the Si substrate and the grown GaAs epitaxial layers was a composite Ge∕Si0.05Ge0.95∕Si0.1Ge0.9 metamorphic layer. We used transmission electron microscopy to observe the microstructures formed in the grown GaAs∕Ge∕SixGe1−x∕Si material and atomic force microscopy to analyze the surface morphology and the formation of antiphase domains in the GaAs epitaxial layers. The measured Hall electron mobility in the channel layer of a MESFET structure grown on a 6° misoriented Si substrate was 2015 cm2 V−1 s−1 with a carrier concentration of 5.0×1017 cm−3. The MESFET device fabricated on this sample exhibited good current-voltage characteristics.

High Critical Electric Field Exceeding 8 MV/cm Measured Using an AlGaN p–i–n Vertical Conducting Diode on n-SiC Substrate

We have succeeded in obtaining the high critical electric field exceeding 8 MV/cm measured using an AlGaN p–i–n vertical conducting diode on n-SiC substrate grown by low-pressure metal organic vapor phase epitaxy. The critical electric field of AlGaN with Al composition of 57% is as high as 8.1 MV/cm, the highest among semiconductors with a doping concentration of less than 1017 cm-3, at which the avalanche multiplication process takes place. The critical electric field is proportional to the bandgap energy to a power of 2.7. In the forward current-voltage characteristics, the on-state resistance of the diode increases with increasing Al composition. Since there is a tradeoff between the breakdown voltage (VB) and the on-state resistance (Ron), the figure of merit VB2/Ron has its maximum when the Al composition is about 30% and is twice as high as that for GaN-based diodes. This indicates that AlGaN-based electronic devices are more promising for high-power operation than GaN-based ones.

Improvement of crystal quality of AlN and AlGaN epitaxial layers by controlling the strain with the (AlN/GaN) multi-buffer layer

AlN and AlGaN epitaxial layers with Al composition of 0.6–0.8 were grown by low-pressure metal organic vapor phase epitaxy on a (0 0 0 1) 6H–SiC substrate using the (AlN/GaN) multi-buffer layer structure (MBLS). Strain of the grown layer could be controlled by structure of the inserted (AlN/GaN) MBLS. It was found that the crystal quality of the grown layer could be improved with increase of the tensile strain in a-axis (compressive strain in c-axis): full-width at half-maximum (FWHM) of X-ray rocking curves (XRC) of both (0 0 0 2) plane ( ω scan) and (1 0 1¯ 2) plane ( ϕ scan) were decreased from 1530 arcsec to 79 arcsec and 3962 arcsec to 853 arcsec for the AlN template, respectively. FWHM of the ϕ scan XRC was several times larger than that of the ω scan, though the former was roughly proportional to the latter.

AlGaInAs selective area growth by LP-MOVPE: experimental characterisation and predictive modelling

Thickness and composition profiles of AlGaInAs-based layers grown by low-pressure metal organic vapour phase epitaxy in the regime of selective area growth (SAG) have been modelled and measured experimentally. Experimental thickness profiles of InP, GaAs and GaAlAs bulk layers grown in the SAG regime have been precisely fitted with a three-dimensional vapour phase-diffusion model, and the characteristic diffusion length coefficient (D/k) for In, Ga and Al extracted. The D/k diffusion parameter for aluminium has been calculated and found intermediate between the indium and gallium ones. The diffusion model predict both thickness and compositional variations of AlGaInAs layers selectively grown for different mask patterns. The excellent agreement obtained between calculated and measured profiles makes this modelling tool essential for engineering of future SAG integrated optical devices.

Effect of growth conditions on the Al composition and quality of AlGaN film

Effects of growth conditions on Al composition and quality of Al x Ga 1− x N epilayer grown by low-pressure matelorganic vapor phase epitaxy (MOVPE) have been investigated. The dependences of Al composition, growth rate and quality on the NH 3 flow rate, TMAl flow rate and growth temperature were studied. The Al composition and quality of Al x Ga 1− x N film depend not only on the TMAl flow rate, but also on the NH 3 flow rate and on the growth temperature. The Al composition of Al x Ga 1− x N film becomes saturated when the gas-phase composition TMAl/(TMAl + TMGa) increases to 0.4, while quality of Al x Ga 1− x N film becomes much worse. The Al composition of Al x Ga 1− x N film increases with increase in the NH 3 flow rate. The quality of Al x Ga 1− x N epilayer is improved when the growth temperature increases. Possible Al incorporation mechanism is discussed.

Aluminum incorporation into AlGaN grown by low-pressure metal organic vapor phase epitaxy

Aluminum (Al) incorporation in AlxGa1−xN films grown by low-pressure metal organic vapor phase epitaxy using trimethylaluminum (TMAl) and trimethylgallium as group III precursors has been systematically studied. The solid phase Al composition of the AlxGa1−xN films varied nonlinearly with the Al gas phase composition. The incorporation kinetics of AlxGa1−xN alloy has been analyzed by using an adsorption-trapping model. Two parameters were used to characterize the properties of Al incorporation, i.e., the capture radius and the adsorption time of Al atoms. An exponential function of the Al composition of the AlxGa1−xN films versus the TMAl gas flow rate was obtained. It was demonstrated that the adsorption time of the Al atom was larger than the growth time of one atomic layer. The effects of ammonia flow rate, crystal growth rate, and growth temperature on the adsorption parameters were also discussed.

High critical electric field of AlxGa1−xN p-i-n vertical conducting diodes on n-SiC substrates

We report the current-voltage characteristics of AlxGa1−xN (x=0–0.22) p-i-n vertical conducting diodes grown on n-SiC substrates by low-pressure metal organic vapor phase epitaxy. An increase in the breakdown voltage was experimentally demonstrated with increasing Al composition. The corresponding critical electric fields were calculated to be 2.4MV∕cm for GaN and 3.5MV∕cm for Al0.22Ga0.78N. The critical electric field is proportional to the band gap energy to a power of 2.5. The forward voltage drop also increases with increasing Al composition but it is still as low as 5.2V even in the case of the Al0.22Ga0.78N p-i-n diode.

Stranski-Krastanov GaN∕AlN quantum dots grown by metal organic vapor phase epitaxy

We report a thorough study of the growth of self-assembled GaN∕AlN quantum dots (QDs). These QDs were grown on sapphire substrates using the Stranski-Krastanov (SK) growth mode by means of low-pressure metal organic vapor phase epitaxy. The influence of the V∕III ratio on the QD height, shape, and density is studied. Emissions above (3.8eV) and below (2.8eV) the band gap of GaN are observed for small dots (1.3nm) and large ones (4.4nm), respectively. Special emphasis was given to the SK growth mode transition and the parameters influencing the QD formation. The two-dimensional–three-dimensional transition is studied continuously by photoluminescence mapping showing its high sensitivity to the V∕III ratio.

P-InGaN/n-GaN Vertical Conducting Diodes on n+-SiC Substrate for High Power Electronic Device Applications

We have investigated the current–voltage (I–V) characteristics of p-InGaN/n-GaN vertical conducting diodes grown on n+-SiC substrates by low-pressure metal organic vapor phase epitaxy (MOVPE). The breakdown voltage (VB) of 250 V was obtained with a low on-state resistance (Ron) of 1.28 mΩ cm2 when the n-GaN layer thickness was increased to 1800 nm, leading to the high figure-of-merit, (VB)2/Ron, of 49 MW/cm2. With increasing measurement temperature from room temperature (RT) to 520 K, the on-state resistance decreased due to the reduced contact resistance of the p-InGaN layer, while the breakdown voltage remained almost constant because of fewer defects in the n-GaN layer. These I–V characteristics are preferable for high-power and high-temperature electronic device applications.

Mechanism of Cluster Formation on Zinc Selenium/Gallium Arsenic Prepared by Metallorganic Vapor Phase Epitaxy

Atomic force microscopy is used to investigate the surface morphology of zinc selenium clusters on gallium arsenic substrate prepared by low-pressure metallorganic vapor phase epitaxy. The density of cluster can reach . The average sizes are 50 nm in height and 112 nm in diameter. From the relationship between the density of cluster and hydrogen selenide flow rate, and the surface and depth compositional variation of zinc and selenium, the ZnSe clusters on GaAs are formed by selenium segregation. The dislocations enhance the selenium segregation. The nonspherical shaped cluster is formed from the mergence of two clusters. The spherical shaped cluster is formed by long-range potential from the nonstoichiometry epi layer.