Organometallic Vapor Phase Epitaxy Reactor Research Articles

Impact of in-situ annealing on dilute-bismide materials and its application to photovoltaics

GaAs1−xBix/GaAs multiple quantum well heterostructures were grown by organo-metallic vapor phase epitaxy (OMVPE) at low temperatures and were subsequently in-situ annealed under an arsine (AsH3) overpressure in the OMVPE reactor. Photoluminescence (PL) measurements were performed to establish the optimized annealing condition for the highest luminescence intensity, as well as high resolution X-ray diffraction (XRD) measurements to detect any structural changes after annealing. In addition, the complex compositional profile and the interfacial abruptness were deduced from the combined XRD analysis with the transmission electron microscopy. A 5-fold increase in the PL intensity at room temperature was observed after annealing under the optimized conditions. Using the optimized annealing conditions, single junction solar cells (SJSC) incorporating 5-period GaAs0.964Bi0.036/GaAs (32nm/20nm) heterostructures for the device base region were fabricated and characterized. The spectral dependence of the external quantum efficiency of the SJSC exhibited improved spectral response as a result of the optimized in-situ annealing, with extended absorption edge up to 1.07eV.

In-situ reflectance monitoring of GaSb substrate oxide desorption

The use of specular reflectance to monitor GaSb substrate oxide desorption in-situ is reported. Substrates were loaded into the organometallic vapor phase epitaxy reactor either as-received (epi-ready) or after receiving a solvent degrease, acid etch and rinse. A variety of surface preparations and anneal conditions were investigated. HCl was used as the etchant, and in certain cases was followed by an additional etch in Br2–HCl–HNO3–CH3COOH for comparison. Rinse comparisons included 2-propanol, methanol, and deionized water. Substrates were heated to either 525°C, 550°C, or 575°C. Features observed in the in-situ reflectance associated with the oxide desorption process are interpreted based on the starting oxide chemistry and thickness. Based on in-situ reflectance and ex-situ atomic force microscopy data, a recommendation on a reproducible GaSb substrate preparation technique suitable for high-quality epitaxial growth is suggested.

Flow Modulation Epitaxial Lateral Overgrowth Of Gallium Nitride On Masked 6H-Silicon Carbide And Sapphire Surfaces

ABSTRACTSelective Area Flow Modulation Epitaxial growth of GaN is carried out in a low pressure Organometallic Vapor Phase Epitaxy reactor. This process is known to enhance reactant surface migration lengths on patterned group III-arsenide and phosphide growth surfaces. With this process, high quality laterally overgrown GaN epitaxial materials result. Under the ammonia rich growth conditions used, enhanced migration (by flux modulation) across masked regions of the substrate has not been observed. The mask materials were silicon dioxide and silicon nitride, both deposited on GaN/AlGaN buffer structures on sapphire and SiC substrates. Window stripes were patterned parallel and perpendicular to the (1100) crystal directions to observe the orientation dependence of the lateral growth rate. Structures exhibited heights above the mask surface as large as 30 microns and atomically smooth surfaces. With a periodic array of stripe window openings in the mask, planarized laterally overgrown surfaces are achieved after roughly 4 microns of overgrowth. Chemical assisted ion beam etching with chlorine gas was used to delineate defects in the selectively grown layers. Additional evidence on the defect reduction is given by Atomic Force and Scanning Transmission Electron Microscopies.

In situ concentration monitoring in a vertical OMVPE reactor by fiber-optics-based Fourier transform infrared spectroscopy

We describe fiber-optics-based Fourier transform infrared (FOB-FTIR) spectroscopy for in situ monitoring of input partial pressures of organometallic precursors in a vertical rotating-disk organometallic vapor phase epitaxy reactor. Detection limits as low as 0.05 Torr for trimethylgallium and 0.006 Torr for tritertiarybutylaluminum (TTBAl) are achieved using a 1 s scan time, which are comparable to established ultrasonic measurements. In addition, the FOB-FTIR approach has the ability to detect parasitic Lewis acid-base interactions between organometallic precursors, as demonstrated for in situ measurements of TTBAl mixed with arsine, trimethylantimony or triethylantimony. Such observations are shown to provide insight into unexpected results in epitaxial growth.

Investigation of the wafer temperature uniformity in an omvpe vertical rotating disk reactor

Measuring the wafer temperature uniformity is one of most difficult problems in the development of organometallic vapor phase epitaxy (OMVPE) equipment. Until recently, the lack of a good experimental technique limited the understanding of OMVPE rotating disk reactor (RDR) thermal dynamic. We have developed a rotating wafer thermal imaging technique, which for the first time allows a real-time experimental investigation of the temperature distribution across the wafer in an RDR under realistic deposition conditions. This technique allows investigation on how process parameters such as the growth temperature (from 650 to 800°C), reactor pressure (from 10 to 620 Torr), reactant flow (from 2 to 30 slm), and wafer carrier rotation speed (from 300 to 1030 rpm) affect the wafer temperature uniformity. This information has allowed us to establish under which conditions single or multi-zone heating should be used in the OMVPE reactor. A wafer temperature uniformity of better than 1°C was demonstrated for both an optimized single zone heating system under a selected combination of process parameters, and for a two-zone heating system over a wide range of the process parameters.

TEM and AFM studies of structural defects in α-GaN films

Interest in wide band-gap GaN and related group-III nitrides has grown recently due to their potential applications for short wavelength optoelectronic devices. One of the main obstacles for their application is the high density of defects formed during heteroepitaxy. Though important progress has been made by using a low temperature A1N buffer layer% recently reported films still contain a defect density (mainly threading dislocations) on the order of 1010 cm-2. This paper reports our current studies of structural defects in α-GaN thin films grown on a-plane (110) and c-plane (0001) sapphire substrates by organometallic vapor phase epitaxy (OMVPE). Atomic force microscopy (AFM), conventional and high resolution transmission electron microscopy (TEM) were used to investigate the nature and origin of these defects.Single crystal α-GaN films were grown using a low temperature A1N or GaN buffer layer in an inductively-heated, water cooled, vertical OMVPE reactor operated at 57 torr.

In-situ X-ray studies of organometallic vapor phase epitaxy growth

In this paper we present an overview of the use of X-ray measurements to determine the atomic mechanisms of organometallic vapor phase epitaxy (OMVPE). Detailed information about OMVPE processes has been difficult to obtain because of the high pressure, chemically reactive environment present during growth. X-ray scattering measurements using very intense synchrotron X-ray sources have been uniquely productive in determining the structure of surfaces during OMVPE growth. For example, surface smoothness, step ordering, growth modes, growth rates and surface reconstructions have been determined. In addition, X-ray spectroscopy measurements have revealed much about the complicated gas phase behavior in the OMVPE reactor. From these scattering and spectroscopy measurements, a more complete model of OMVPE growth is being developed.

Adjusting trimethylgallium injection time to explore atomic layer epitaxy of GaAs between 425 and 500°C by organometallic vapor phase epitaxy

In experiments employing a conventional low-pressure, rotating-disk organome-tallic vapor phase epitaxy reactor, GaAs epilayers have been grown at substrate temperatures ranging from 425 to 500°C by exposing the substrate alternately to trimethylgallium (TMG) and AsH3.The GaAs growth rateR was approximately constant with TMG flow rate, but with increasing TMG injection timet, it increased to more than one monolayer per TMG/AsH3 cycle without saturating. Although growth was not self-limiting, for one specific combination of temperature andt, a value of R = 1 monolayer/cycle could be achieved by usingt values decreasing from 10.8 s at 425°C to 0.9 s at 500°C in accordance with an Arrhenius relationship between 1/t and absolute temperature.

A technique for eliminating white phosphorus deposits in vapor phase epitaxy systems

A technique of heating the exhaust lines is described whereby phosphorus in the exhaust portion of an organometallic vapor phase epitaxy reactor is encouraged to deposit in the red form rather than the pyrophoric white form. This technique is simple, effective, and does not hinder or limit the conditions under which the reactor may be operated.

Material characterization of GaAs grown in a novel OMVPE reactor

Abstract A novel organometallic vapor phase epitaxy reactor was designed and fabricated to achieve good material quality, high deposition efficiency, and uniformity over large-area substrates. GaAs epitaxial layers were grown under various conditions to study material characteristics such as morphology, mobility, carrier concentration, minority carrier lifetime and uniformity. Effective minority carrier lifetimes of 120 ns have been obtained in this reactor and methods of obtaining further improvements in this parameter are discussed. Doped and undoped GaAs epitaxial layers were grown on 2″ diameter substrates to study large-area uniformity characteristics. Thickness non-uniformity was founf to be dominated by edge effects due to the presence of the susceptor lip which supports the samples. Doping non-uniformity was caused by variations in surface temperature over the water.

OMVPE regrowth of CH3I-vapor-etched GaAs

In experiments on the interrupted growth of GaAs by organometallic vapor phase epitaxy (OMVPE), we have compared the properties of two types of epilayers: those grown on CH3I-vapor-etched first epilayers and those grown on first epilayers that were either untreated or etched with H2SO4. The OMVPE growth and CH3I etching were performed in two different reactors, and each sample was briefly exposed to air immediately before being placed in the OMVPE reactor for growth of the second epilayer. For CH3I etch temperatures below 500° C, the two types of second epilayers are comparable in surface morphology, as characterized by Nomarski interference microscopy, and in optical quality, as characterized by low-temperature photoluminescence measurements. Electrical characterization by C-V depth profiling shows that electron accumulation at the regrowth interface is increased very little by CH3I etching. Such etching prior to regrowth eliminates most of the electron accumulation resulting from H2SO4 etching of the first epilayer.

The effect of oxygen incorporation in semi-insulating (AlxGa1−x)yIn1−yP

Oxygen-doped, semi-insulating layers of (AlxGa1−x)yIn1−yP with x=0.4 were grown on GaAs using organometallic vapor phase epitaxy (OMVPE). Secondary-ion mass spectrometry measurements show that the oxygen incorporation is proportional to the flow rate of O2 into the OMVPE reactor. Two-terminal metal-insulator-semiconductor devices were fabricated and used to evaluate the electrical characteristics of the (AlxGa1−x)yIn1−yP. Traps into the (AlxGa1−x)yIn1−yP bulk behave like DX centers, and are believed to be related to residual Si contamination. Increasing the oxygen concentration in the (AlxGa1−x)yIn1−yP layer decreases the trap concentration by the formation of oxygen complexes with the Si atoms.

Pyrolysis Studies and Deposition of Sb Films Using the Novel Omvpe Source (I-Pr)2 SbH

ABSTRACTThe novel antimony source compound di-isopropylantimony hydride, (i-Pr)2 was synthesized and evaluated for use as a volatile Sb-source compound for low temperature growth of Sb-containing semiconductor materials. (i-Pr)2SbH was pyrolyzed in a horizontal atmospheric pressure organometallic vapor phase epitaxy (OMVPE) reactor using Arand H2 as carrier gases. The gaseous exhaust products were analyzed by a residual gas analyzer. Complete pyrolysis of (i-Pr)2SbH in our OMVPE reactor occursaround 300°C and 350°C in Ar and H2, respectively. A comparison between the pyrolysis temperatures and pyrolysis byproducts with respect to a proposed decomposition mechanism of (i-Pr)2SbH is presented. Sb films were grown on Si(100) andSi(111) as low as 200° C. The Sb films were analyzed by Auger and X-ray diffraction. These polycrystalline Sb films were free of detectable carbon by AES. X-ray diffraction data indicated that these Sb films were highly oriented in the [000L] direction.

The Effect of Wall Heating in Horizontal Organometallic Vapor Phase Epitaxial Reactors

Numerical solutions of the conservation of mass, momentum, and energy equations in a horizontal organometallic vapor phase epitaxial reactor have been obtained for different temperature boundary conditions. The idealized case of isothermal reactor walls was compared to the physically realistic case of a wall which interacts radiatively and convectively with its surroundings. The thermal radiation analysis includes a two‐band model for the nongray, semitransparent, quartz walls of the reactor. The radiation analysis is coupled with convection to (or from) the gas on the inside and to the ambient on the outside of the reactor. Wall heating is shown to have a substantial effect on the velocity and temperature fields in the reactor. The simulated temperature fields show a close match with experimental results. The temperature distribution along the wall for the radiation case was compared with the isothermal case. Finally, the effect on growth rate along the susceptor was studied.

A novel reactor for large-area epitaxial solar cell materials

Abstract A novel vertical stagnation flow organometallic vapor phase epitaxy reactor was designed and fabricated for the growth of GaAs and AlGaAs for solar cell applications. The reactor had an inverted configuration to eliminate recirculation problems. The susceptor and gas inlet nozzle were closely spaced (about 1 cm) in order to achieve improvements in deposition efficiency, layer uniformity and abruptness of interfaces. A specially designed water-cooled inlet nozzle was used to maintain the nozzle surface at relatively low temperatures under all operating conditions. A computer model was formulated to study the various thermal processes in this reactor. The model used rigorous thermal boundary conditions which included thermal radiation effects. Simulated and experimental nozzle temperatures were compared for different susceptor temperatures, susceptor-nozzle distances, gas flow rates and reactor pressures. The maximum nozzle temperature was about 100 °C, which is sufficiently low to prevent premature decomposition of the reactants on its surface.

Atmospheric pressure organometallic vapor phase epitaxy growth of high-mobility GaAs using trimethylgallium and arsine

Epitaxial layers of GaAs with peak mobilities as high as 200 000 cm2/V s at 50 K have been grown in an atmospheric pressure organometallic vapor phase epitaxy reactor using trimethylgallium (TMG) and arsine. The growth conditions which lead to high-mobility GaAs are described in this letter. Low-temperature photoluminescence and temperature-dependent Hall measurements are used to study the dependence of the incorporation of residual impurities on the growth temperature and arsine partial pressure. Carbon acceptor densities <1014 cm−3 were measured in the highest purity samples.

On-demand atmospheric pressure storage system for AsH3 and PH3

An on-demand atmospheric pressure storage system for AsH3 and PH3, which eliminates the sudden release hazard associated with compressed gases, has been developed and tested with AsH3. The storage system is based on the adsorption of these gases into the microcavities of synthetic zeolites at 23 °C and subsequent desorption at higher temperatures. The adsorption isotherm and isobar of AsH3 on NaA and CaA zeolites were measured. At 23 °C and 760 Torr AsH3 pressure, an adsorption capacity of 25 wt. % (AsH3/zeolite) was measured for CaA zeolite. About 100% of the adsorbed AsH3 was recovered at desorption temperatures below 190 °C. Preliminary results of operating a 500 cc prototype AsH3-zeolite storage system connected to an organometallic vapor phase epitaxy reactor for the growth of GaAs and AlGaAs show that the purity of the AsH3 is retained during the adsorption/desorption process.

ChemInform Abstract: Efficiency of Activated Carbon for the Removal of Diethyltellurium from a Carrier Gas Stream.

AbstractBecause of its toxicity, which is comparable to elemental Te, the efficient removal of diethyltellurium from the effluent of an organometallic vapor phase epitaxy reactor is very desirable.

Alkyl exchange effects between triethylindium and trimethylgallium

A study of the room temperature gas-phase interactions between gallium and indium alkyls was undertaken using a specially designed mass spectrometer sampling system, mounted on a conventional, low pressure organometallic vapor phase epitaxial reactor. Mixtures of triethylindium with triethylgallium were investigates. Both combinations formed addition compounds; moreover, the triethylindium-trimethygallium mizture also underwent alkyl exchange. The effect of these admixtures on the reaction between triethylindium and arsine was also investigated, and both admixtures showed reduced reactivity towards arsine. A structure for the addition compound, consistent with our observations, was proposed.

Highly Strained InAsxPl-X/InP Quantum wells Prepared by Flow Modulation Epitaxy

AbstractFlow modulation techniques have been used to prepare highly strained InAsxPl-x/InP quantum well structures in an atmospheric pressure organometallic vapor phase epitaxial reactor. The compositions of the pseudomorphic wells ranged from x=0.40 to 0.74, corresponding to biaxial compressive strains of 1.3-2.4%. Well thicknesses ranged from 2 to 26 monolayers. The flow modulation growth conditions were found to have a strong influence on interface formation in the wells. For wells grown under optimized modulation conditions, low-temperature photoluminescence spectra revealed peak-splitting of the emission from the thinnest wells. This splitting is attributed to emission from regions in the wells with atomically smooth interfaces over areas greater in lateral extent than the exciton diameter. The full-width at half-maximum of the peaks is in the 6-15 meV range, comparable to the best reported values for lattice- matched InGaAs(P)/InP quantum wells grown by any technique, and is independent of well thickness or composition.