Organic Chemical Vapor Deposition Growth Research Articles

The evaluation of bond dissociation energies for simple sulphur containing molecules using ab initio and density functional methods

The S–H and C–S bond dissociation energies for simple alkylthiols and dialkylsulphides, along with the S–S bond dissociation energy for dimethyl disulphide, compounds which have been used in the metal–organic chemical vapour deposition (MOCVD) growth of wide band gap II–VI (12–16) Zn- and Cd-based compound semiconductors, have been computed using the ab initio (ROHF and MP2) and density functional theory (DFT) methods (BHandH, BHandHLYP, B3LYP, B3P86, B3PW91, BLYP and BP86) with the 6-311+G(2d,p) basis set along with high accuracy complete basis set, CBS-4 and CBS-Q energy computations. The computed energies are compared with experimental results and the suitability of the DFT methods, for the computational study of these systems, is discussed.

Unintentional hydrogenation of GaN and related alloys during processing

Atomic hydrogen plays an important role in GaN, passivating the electrical activity of Mg acceptors during cooldown after metal organic chemical vapor deposition growth, and thereby preventing achievement of high p-type doping levels unless an annealing step is performed. We have found that hydrogen is easily incorporated into GaN and related materials during many different process steps, including boiling in water, wet chemical etching in KOH-based solutions, dielectric deposition using SiH4 or dry etching in Cl2/CH4/H2Ar electron cyclotron resonance plasmas. In each of these cases we have employed deuterated chemicals and detected the incorporation of deuterium into GaN using high sensitivity secondary ion mass spectroscopy measurements. Hydrogen is found to have a diffusivity of ≳10−11 cm2 s−1 at 170 °C, and to passivate the electrical activity of Mg and C acceptors and also the native shallow donors in InGaN and InAlN. Annealing at 450–500 °C restores the electrical activity, but the hydrogen does not physically leave the films until much higher (∼800 °C) temperatures. The activation energies for dopant reactivation are of the order of 2.5 eV in bulk samples, where hydrogen retrapping is expected to be significant.

Quantum energy control of multiple‐quantum‐well structures by selective area mocvd and its application to photonic integrated devices

AbstractQuantum energy control is proposed in the form of a multiple‐quantum‐well (MQW) structure fabricated by selective metal organic chemical vapor deposition (MOCVD) growth to obtain high‐performance multiple‐function semiconductor photonic integrated devices. Its fundamental principle and the applied photonic integrated device are discussed. In general, semiconductor photonic integrated devices require semiconductor layers with different bandgap‐energy states for each structural device having a different function formed on the same semiconductor substrate.In this paper, the position‐dependent growth speed and the growth‐layer compositions on the substrate are controlled by selective MOCVD growth so that the quantum energy levels of the InGaAs/InP MQW structures grown simultaneously are varied over the substrate surface. As a result, a controllable range of the quantum energy level spanning over 200 meV and a high‐quality crystal configuration of selectively grown layers comparable to that formed by conventional growth processes have been confirmed.Application of this new integration method required that we design a monolithic integrated device of a distributed feedback laser diode and an electric field absorption‐type modulator, as well as a multiple‐wavelength distributed feedback laser array. Despite the simple design method, good crystal quality of the selectively grown layers, good optical coupling between the devices, and good device performance were observed.

Thermally annealed GaN nucleation layers and the device-quality metal organic chemical vapor deposition growth of Si-doped GaN films on (00.1) sapphire

The effect of epitaxial growth temperature (985–1050 °C) on the properties of Si-doped GaN layers on self-nucleated (00.1) sapphire has been investigated. Several device-related properties monotonically improve with increasing growth temperature, including (a) carrier density and (b) volume fraction of heteroepitaxial domains. However, a number of equally important device-related properties show a local maximum and include (a) optical second-harmonic generation intensity, (b) structural coherence, and particularly (c) surface morphology. The antecedents of the first class lie in increases in surface and bulk diffusion and reductions in film defect incorporation and stress at the GaN/GaN (nucleation layer)/α-Al2O3 heterointerface. The second class arises from the quite limited range over which the thermally annealed GaN nucleation layer stimulates pseudo-two-dimensional growth of the GaN overlayer.

A kinetic model for the growth of znte by metal organic chemical vapour deposition

AbstractA kinetic model for the metal organic chemical vapour deposition (MOCVD) growth of ZnTe is presented, taking into account the competitive adsorption of organometallic precursors. By assuming that diethylzinc (DEZn) and diethyltellurium (DETe) or di‐isopropyltellurium (DIpTe) are adsorbed onto the surface by two sites, the model yields the growth rate as a function of the gas‐phase concentrations of the constitutents and is corroborated by experimental results obtained by the MOCVD growth (at 400°C with DETe or 350°C with DIpTe), which shows asymmetric behaviour: for a given DETe or DIpTe pressure (10−4 atm), the growth rate as a function of DEZn partial pressure passes through a maximum, whereas, at the same constant DEZn pressure, the growth rate increases monotonically when the DETe or DIpTe partial pressure increases

Idea on Momentum Effect of Gaseous Beam Particles on Epitaxial Crystal Stiffness as to Thin Film Growth Such as Metal Organic Chemical Vapor Deposition Growth and Molecular Beam Growth

AbstractThe author reports on idea of momentum effect of gaseous beam particles as to thin film epitaxial crystal growth such as molecular beam epitaxial growth or metal organic chemical vapor deposition epitaxial growth on stiffness of epitaxial growth thin film. The author presented that liquid glass encapsulation squeeze compression effect of liquid-glass-encapsulation Czochralski technique (LEC) crystal growth [Y.Saito, presented at the 10th Int. Conf. on Crystal Growth, 1992], third element different from crystal matrix elements [Y.Saito, presented at the 9th Int. Conf. on Ternary and Multinary Compounds, 1993], light momentum pressure of substance cooling thermal cycle [Y.Saito, presented at the 1st Int.Symposium on Laser and Optoelectronics Technology & Applications, 1993] can yield firmly binded bonds of substance elements. On the other hand, collisions of particles sputtered from solid target slabs [Y.Saito, presented at the 2nd Int.Symposium on Sputtering & Plasma Processes, 1993] or accelerated ions or particles evaporated from molten metals with themselves on the thin films can yield binded bonds. It was shown that internal compression in a crystal by ion implantation in crystal cell lattices can make the refractory state to gas phase chemical attack.[Y.Saito, in the Materials Research Society Symposium Proc. Vol. 279, pp. 135–140.] From these results, we can consider momentum effect at collision on binding state. After collision binding, internal compression by thermal transition variation in a multilayer structure during cooling thermal cycle influences binding stiffness.

Metal–Organic chemical vapour deposition (mocvd) growth utilising cu(acac)2 (acac  pentane‐3, 5‐dionato) as a source for copper‐containing materials: Influence of carrier gas on surface morphology

AbstractThe unsubstituted bis‐β‐diketonato complex of copper, Cu(acac)2 (acac  pentane‐3, 5‐dionato), has been used to deposit both elemental copper and copper oxide thin films by metal–organic chemical vapour deposition (MOCVD). For all Cu(II) bis‐β‐diketonates, growth of oxygen‐free layers requires the breakage of four copper–oxygen bonds present in the precursor. The influence of carrier gas composition on deposit morphology has been examined for six parameter sets: both hydrous and anhydrous streams, each for reducing (H2), inert (Ar) and oxidising (O2) environments.

In-situ plasma cleaning of stainless steel III-V MOCVD growth systems

A plasma enhanced, in-situ, dry etching process for the cleaning of stainless steel III-V Metal Organic Chemical Vapor Deposition growth systems was investigated as a function of etchant gas, flow rate, electrode configuration, power density and plasma frequency. The plasma enhanced etching process was investigated using Ar, CH4 (5% in H2), CCl2F2 (Freon 12)/Ar and Cl2/Ar plasmas with flows varying from 5 to 25 seem. The plasma was excited using three electrode configurations, and two radio frequency generators (90–460 KHz and 13.56 MHz), singly and in combination. The plasma power was varied over the range from 200 to 700 Watts (∼0.2W/cm2 – 0.7W/cm2). The etching rates of GaAs, InP, As, and Mo were measured using a weight difference method. The Cl2/Ar plasmas exhibited etching rates typically 5 to 10 times greater than that of CCl2F2 plasmas, which in turn is several times greater than that of the other etchant gases investigated. At 400 W, elemental As etch rates, as high as ∼180μm/hr and ∼20μm/hr were achieved using Cl2 and CCl2F2 plasmas, respectively. InP/GaAs etch rates using Cl2 were ∼30μm/hr and using CCl2F2 were ∼7μm/hr. Plasma characteristics and etch rate measurements are reported. The in-situ process investigated is a safe, cost effective and an efficient method for increasing reactor uptime.

Growth and process optimization of CdTe and CdZnTe polycrystalline films for high efficiency solar cells

Abstract Polycrystalline CdTe solar cells with efficiencies of approximately 10% were achieved by metal organic chemical vapor deposition growth of CdTe on glass/SnO 2 /CdS substrates. An in situ pre-heat treatment of the CdS substrate at 450 °C in an H 2 ambient was found to be essential for high performance devices because it removes oxygen-related defects on the CdS surface. This heat treatment also results in a cadmium-deficient CdS surface which may, in part, limit the CdTe cell efficiency to 10% owing to cadmium vacancy related interface defects. The CdCl 2 treatment used in CdTe cell processing was found to promote grain growth, reduce series resistance and interface state density, and change to dominant current transport mechanism from thermally assisted tunneling and recombination via interface states to recombination in the depletion region. These beneficial effects resulted in an increase in the CdTe/CdS cell efficiency from around 2% to approximately 9%. In addition to the CdTe cells, polycrystalline 1.7 eV CdZnTe films were grown by molecular beam epitaxy for tandem cell applications. CdZnTe/CdS cells processed using the standard CdTe cell fabrication procedure resulted in 4.4% efficiency, high series resistance, and a band gap shift to 1.55 eV. Formation of ZnO at and near the CdZnTe surface was found to be the source of high contact resistance. A saturated dichromate etch instead of the Br 2 :CH 3 OH etch prior to contact deposition was found to solve the contact resistance problem. The CdCl 2 treatment was identified to be the cause of the observed band gap shift owing to the preferred formation of ZnCl 2 . A model for the band gap shift along with a possible solution using an overpressure of ZnCl 2 in the annealing ambient is proposed. Development of a sintering aid which promotes grain growth and preserves the optimum 1.7 eV band gap is shown to be the key successful wide gap CdZnTe cells.

Metal Organic Chemical Vapor Deposition Growth of GaAs on Si Using GaAs Buffer Layer Grown by an Alternate Gas Flow of Source Materials

We tried the atomic layer epitaxy (ALE) growth of GaAs initial layer in a two-step growth of GaAs on Si by a conventional metal organic chemical vapor deposition (MOCVD) system. The etch pit density of GaAs overlayer became smaller than that without this approach. The cross sectional transmission electron microscope (TEM) of this sample indicated that the improvement of crystalline quality of GaAs overlayer was attributed to the smooth interface structure of GaAs/Si due to the layer by layer growth of the buffer layer.

Growth and properties of GaSb, Ga 1- xIn xSb and Ga 1- xAl xSb epilayers by MOCVD

GaSb-based compound semiconductors are suitable materials for low-noise avalanche photo-diodes(APD's) and long wavelength laser diodes and photodetectors. In this paper, we review the metal organic chemical vapor deposition (MOCVD) growth conditions and the properties of GaSb, GaInSb and AlGaSb epitaxial layers, including the effects of III/V ratio, growth temperature, pressure and growth rate on electrical quality, optical properties, surface morphology and solid distribution coefficients.

In situ characterization by reflectance difference spectroscopy of III–V materials and heterojunctions grown by low pressure metal organic chemical vapour deposition

The reflectance difference spectroscopy (RDS) technique has recently been used successfully to study the molecular beam epitaxial growth of GaAs and AlAs. An extension of such in situ characterization to the metal organic chemical vapour deposition (MOCVD) growth of III–V compounds would be very helpful, because electronic measurements such as reflection high energy electron diffraction are not possible in the MOCVD growth environment. In this paper preliminary results are reported of RDS studies performed in a low pressure MOCVD reactor under optimal growth conditions. The RDS signatures of GaInAsInP and GaAsGaInP heterojunctions and superlattices are presented for the first time. It is possible using the RDS technique to determine in situ the ⪡011⪢ and ⪡01 1⪢ directions of III–V compounds in a non-destructive way, which is very important for technological applications. A study of InAs growth suggests that one can have access to the III:V ratio on the surface using this technique. The occurrence of very large surface anisotropies (10% or more) related to the growth of lattice mismatched materials is reported.

Metal–organic chemical vapor deposition hybrid substrates for HgCdTe

This paper describes the process we used in selecting GaAs and InP as the best foreign (non-CdTe) substrates for metal–organic chemical vapor deposition (MOCVD) growth of CdTe to form hybrid substrates suitable for use as substrates for epitaxial growth of HgCdTe. We describe the MOCVD growth process and give typical characterization results. We carried out a 12 run statistical design experiment to identify the most important parameters which turned out to be the metal–organic pressures and the growth temperature. These hybrid substrates have been used for the growth of HgCdTe by liquid-phase epitaxy (LPE). Responsivity of 104 V/W is reported for Hg0.7Cd0.3Te with 3.5×1015 donors/cm3 grown on a long wavelength infrared (LWIR) transparent hybrid substrate.

Low pressure-MOCVD growth of Ga0.47In0.53As–InP heterojunction and superlattices

We report the latest results of a continuing study of low pressure-metal–organic chemical vapor deposition (LP-MOCVD) growth of InP and Ga0.47In0.53As–InP heterojunctions and superlattices, which describe the general growth of InP and GaInAs with specific application to quantum well heterostructure. A study of the sources and control of residual impurities in InP and Ga0.47In0.53As, the effects of source purity upon residual impurities, mobility, and 2 K PL intensity are detailed. Total impurity concentrations as low as 6×1014 cm−3 for InP and 3×1014 cm−3 for Ga0.47In0.53As have been obtained. Mobility as high as=μ (300)=5350, μ (77)=60 000 cm2 V−1 s−1 for InP, and μ (300)=12 000, μ (77)=60 000, μ (2)=100 000 cm2 V−1 s−1 for GaInAs layers have been measured.