Organometallic Chemical Vapor Deposition Research Articles

Vertically stacked multiple-quantum-wire semiconductor diode lasers

We report the structure and lasing characteristics of GaAs/AlGaAs vertically stacked multiple-quantum-wire (QWR) semiconductor lasers grown by organometallic chemical vapor deposition on V-grooved substrates. The active region in these lasers consists of three crescent-shaped wires, placed at the center of a single-mode optical waveguide. The higher optical confinement factor, compared to single-QWR structures, leads to reduced threshold currents, as low as 0.6 mA for high-reflection coated devices at room temperature. The lower threshold carrier density results in oscillation at a lower QWR subband as compared to single-QWR laser structures.

In situ definition of semiconductor structures by selective area growth and etching

Selective area growth (etching) by low-pressure organometallic chemical vapor deposition (LP-OMCVD) is utilized to intentionally modulate the local growth (etch) rate by choosing the pattern of dielectric-masked areas, thereby defining III-V semiconductor structures in situ. This technique is applied to tune the emission wavelength of a GaAs/AlGaAs quantum well structure, and to obtain InP/InGaAs superlattice structures tapered in thickness with growth rate increases as high as 800%, suitable for integrated optics applications. In contrast, selective deposition by organometallic molecular beam epitaxy (OMMBE) does not produce growth rate enhancements, thereby preventing similar in situ definition schemes but allowing to integrate structures with optimized nominal thicknesses.

Regrowth of In0.53Ga0.47As/InP p-n heterojunctions by organometallic chemical vapor deposition

The quality of interfaces regrown by organometallic chemical vapor deposition is evaluated from the electrical characteristics of In0.53Ga0.47As/InP p-n heterojunction diodes. The I-V curves are undistinguishable from those of junctions obtained by continuous growth, with ideality factors η≊1.1 and no observable contribution from interface recombination in the measured current range. An upper limit of 200 cm/s is obtained for the interface recombination velocity. The results show that high-quality interfaces can be obtained in spite of prior air exposure. The technique can be used for the realization of regrown heterojunction bipolar transistors.

Pulsed organometallic beam epitaxy of complex oxide films

We report the results of a pulsed organometallic beam epitaxy (POMBE) process for growing complex oxide films at low background gas pressure (10−4–10−2 Torr) and low substrate temperature (600–680 °C) using organometallic precursors in an oxygen plasma environment. Our results show that POMBE can extend the capability of organometallic chemical vapor deposition to growing complex oxide films with high precision both in composition and structure without the need for post-deposition oxidation and heat treatments. The growth of phase-pure, highly oriented Y-Ba-Cu-O superconducting oxide films {[Tc (R=0)=90.5 K] and Jc (77 K, 50 K gauss)=1.1×105 A/cm2} is given as an example. Similar to the pulsed laser deposition process, the POMBE method has the potential for in situ processing of multilayer structures (e.g., junctions).

Novel etching technique for a buried heterostructure GaInAs/AlGaInAs quantum-well laser diode

A novel etching technique for the 1.5-μm GaInAs/AlGaInAs buried heterostructure quantum-well laser diode is developed. Tartaric acid is used for the etching of GaInAs and AlGaInAs layers for the first time. Using a three-step material-selective etching, a 3-μm-high mesa with about 1.5-μm-wide active layer and 3-μm-wide contact layer can be achieved with good reproducibility. Nearly flat surfaces were obtained after a two-step organometallic chemical vapor deposition growth. A low threshold current of 11 mA was obtained for a 570-μm-long cavity device.

Characterization of chromium nitride and carbonitride coatings deposited at low temperature by organometallic chemical vapour deposition

Chromium nitride and carbonitride hard coatings were deposited by organometallic chemical vapour deposition in the temperature range 350–550 °C. Bis(benzene) chromium and NH 3 or N 2H 4 were used as chromium and nitrogen vapour sources respectively. The chemical and structural characterization of these coatings is presented. Amorphous films were obtained below 450 °C. Above this temperature, a different phase, namely Cr 7C 3, Cr 2 (N,C) or CrN could be prepared depending on the gas phase composition. Electron probe microanalysis and X-ray photoelectron spectroscopy gave evidence for a slight contamination of the films with free carbon. The experimental results are in good agreement with a thermodynamic calculation which has been fruitful in giving information about the feasibility of growing chromium nitride phases under these chemical vapour deposition conditions. The microhardness of the coating in each case was comparable with that of similar material deposited by other techniques.

A modified harmonic oscillator approximation scheme for the dielectric constants of AlxGa1−xAs

The dielectric functions of AlxGa1−xAs have recently been measured for several Al mole fractions over the 1.5–6.0 eV wavelength range [D.E. Aspnes, S. M. Kelso, R. A. Logan, and R. Bhat, J. Appl. Phys. 60, 754 (1986)]. To make use of this data to perform optical modeling for spectroscopic ellipsometry analysis of AlxGa1−xAs-containing samples, and for other optical modeling purposes, a reasonable interpolation scheme is required to estimate the dielectric functions of intermediate compounds. In this work, we will present a modified version of the harmonic oscillator approximation (HOA) of Erman et al. [M. Erman, J. B. Theeten, P. Chambon, S. M. Kelso, and D. E. Aspnes, J. Appl. Phys. 56, 2664 (1984)] to model the experimental data and interpolate between the known compositions over the 1.5–5.0 eV range. Our model uses additional harmonic oscillators and allows each oscillator to have an independent phase. These modifications significantly improve the accuracy of the approximation for photon energies at and below the fundamental band-gap energy. This allows much more accurate modeling of reflection problems for multilayer GaAs/AlGaAs structures. We will present test of this approach with simulations of spectroscopic ellipsometry data using known data, and with measured spectroscopic ellipsometer data on AlxGa1−xAs-containing samples grown by molecular-beam epitaxy and organometallic chemical vapor deposition.

The thermal stability of lattice mismatched InGaAs grown on patterned GaAs

Patterning and etching substrates into mesas separated by trenches before the growth of mismatched (by about 1% or less) epitaxial layers considerably reduces the interface misfit dislocation density when the layer thickness exceeds the critical thickness. Such films are in a metastable state, since misfit dislocations allow the epitaxial layers to relax to an in-plane lattice parameter closer to its strain-free value. Thermal annealing (from 600 to 850° C) has been used to study the stability of these structures to explore the properties of the misfit dislocations and their formation. The misfit dislocation density was determined by counting the dark line defects at the InGaAs/GaAs interface, imaged by scanning cathodoluminescence. InGaAs epitaxial layers grown on patterned GaAs substrates by organometallic chemical vapor deposition possess a very small as-grown misfit dislocation density, and even after severe annealing for up to 300 sec at 800° C the defect density is less than 1500 cm−1 for a In0.04Ga0.96As, 300 nm thick layer (about 25% of the dislocation density found in unpatterned material that has not been annealed). The misfit dislocation nucleation properties of the material are found to depend on the trench depth; samples made with deeper (greater than 0.5 μm) trenches are more stable. Molecular beam epitaxially grown layers are much less stable than the above material; misfit dislocations nucleate in much greater numbers than in comparable organo-metallic chemical vapor deposited material at all of the temperatures studied.

Physicochemical properties of dimethylzinc, dimethylcadmium and diethylzinc

AbstractPhysicochemical properties of dimethylzinc, dimethylcadmium and diethylzinc have been investigated by means of vapor pressure measurement, mass spectroscopy and gas chromatography. The saturated vapor pressure‐temperature dependence of these alkyl organometallics was determined to be as followsmagnified imageThe temperature ranges for vapor phase decomposition for deposition of each metal were clarified, and vapor‐phase species released in the decompositions were investigated. These investigations on the organometallics are to provide basic material data for the establishment of organometallic chemical vapor deposition techniques for Group IIB‐VI compounds.

Effects of mesa area and orientation on defects in strained InxGa1−xAs films grown by LPOMCVD

We have selectively grown InxGa1−xAs (0.04 <x < 0.20, 200 − 7000A) on rectangular growth areas (100 μm by 200 mil) patterned on GaAs substrates with very low etch pit densities (∼200 cm−2). The edge orientations of the growth areas were varied on the substrate resulting in distinct facet formation on the deposited mesa structures. Layers were grown using Low-Pressure Organometallic Chemical Vapor Deposition (LPOMCVD) and all samples were annealed for 1 hr at 700° C. Indium content and film thicknesses were very uniform across a wafer so that only the facet shape was varied. Observation of Crosshatch defect densities as a function of growth window orientation showed that 2900A In0.08Ga0.92As mesas with [010] edge orientations exhibited no Crosshatch defects. Identical mesas grown in windows with other edge orientations exhibited varying crosshatch defect densities. Large unpatterned areas of growth were heavily crosshatched. This variation in Crosshatch defect density as a function of mesa orientation appears to be associated with non-area related dislocation nucleation mechanisms at the mesa edges. Proper choice of window orientation for patterned substrate epitaxy will allow the mesa facets to be controlled thereby reducing misfit dislocations in the heterostructure interface.

Effects of in situ treatment on InGaAs/InP heterointerfaces produced by organometallic chemical vapor deposition regrowth

The properties of heterostructures containing an InGaAs/InP heterointerface generated by organometallic chemical vapor deposition regrowth have been investigated. Regrowth of InGaAs on InP was carried out after different sample preparations including wet chemical etching and in situ treatment prior to the regrowth. The electrical properties of the heterointerface were studied by performing deep-level transient spectroscopy measurements. An electron trap was observed in the interface region of the samples either in situ etched with HCl gas or annealed under PH3 overpressure. Temporal pulse response measurements were employed to study the effects of this electron trap on the optical performance of p-i-n photodetectors containing this regrown heterointerface.

Epitaxial PbTiO3 thin films grown by organometallic chemical vapor deposition

Epitaxial PbTiO3 layers have been grown on (001)SrTiO3 substrates by organometallic chemical vapor deposition using the precursors titanium-iso-propoxide and tetra-ethyl-lead. The growth temperature for these films was around 700 °C. The epitaxial nature of c-axis-oriented PbTiO3 is confirmed by Rutherford backscattering spectrometry, x-ray diffraction, including pole figure analysis, and high-resolution electron microscopy (HREM). With HREM twinning has been observed.

Influence of trench depth on the misfit dislocation density at strained epitaxial layer interfaces grown on patterned GaAs substrates

The number of misfit dislocations in strained, epitaxial InGaAs layers can be significantly reduced by growing on patterned substrates. Etched trenches on these substrates block misfit dislocation propagation from mesa to mesa. To determine the minimum trench depth needed to block misfit dislocations, 200 μm×200 μm mesas separated by 10-μm-wide trenches of varying depths were etched into a GaAs substrate before organometallic chemical vapor deposition of 300 or 600 nm In0.04Ga0.96As strained layers (several times the critical thickness). Three isolation regimes are seen in the 300-nm-thick InGaAs samples. The shallowest trenches, regime I, below 300 nm, do not completely block all dislocations. Misfit dislocations are blocked by trenches 300–500 nm deep, regime II, after they glide down the mesa walls and stop at the far side of the trenches. Trenches greater than 500 nm, regime III, stop dislocations at the mesa edges. The 600-nm-thick InGaAs layers with trench depths greater than 450 nm completely stopped all misfit dislocations. The third regime did not occur for trenches as deep as 650 nm. These results show that the epitaxial layer does not have to be discontinuous to prevent misfit dislocations from gliding across patterned substrates.

Real-time optical diagnostics for epitaxial growth

A variety of optical methods is now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy, organometallic chemical vapor deposition, and related techniques. New capabilities for surface analysis are provided by new techniques such as reflectance-difference spectroscopy, which use intrinsic symmetries to suppress ordinarily dominant bulk contributions. Bulk and microstructural properties such as compositions and layer thicknesses can be determined directly by techniques such as spectroellipsometry, which return information integrated over the penetration depth of light. Proven capabilities suggest new applications to interrupted growth and to metastable materials systems involving self-ordering and strain relaxation. The first closed-loop system for controlling semiconductor crystal growth, which uses a spectroellipsometer as the monitoring element, is briefly described.

ChemInform Abstract: Growth and Characterization of Thin Films of Thallium(III) Oxide by Organometallic Chemical Vapor Deposition.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Substrate effects on the epitaxial growth of ZnGeP2 thin films by open tube organometallic chemical vapor deposition

In this paper, we report the growth of epitaxial films of ZnGeP2 on GaP and Si substrates of (001) and (111) orientations by open tube organometallic chemical vapor deposition. Generally, smaller growth rates are required to achieve similar film quality on (111) GaP as compared to growth on (001). For the growth on (001) GaP the c-axis strain determined by x-ray diffraction agrees with the expected strain for a lattice mismatch of 0.0026 between the a-axis lattice parameters of ZnGeP2 and GaP. Based on the continuous increase of the c-axis lattice parameters and the gradual weakening of the chalcopyrite structure superlattice reflections, a continuous transition is proposed from the ordered structure of ZnGeP2 towards diamond structure of Ge via partially disordered metastable solid solution of ZnGeP2-Ge. Cross-sectional transmission electron microscopy reveals twinning of epitaxial ZnGeP2-Ge films on (111) GaP. The twinning density is related to both the growth rate and the flow rate ratio of Zn(CH3)2 to GeH4 at constant flow rate of PH3 and H2. Twins are also formed in ZnGeP2 growth on Si substrates.

Anisotropic transport in a modulation-doped GaAs quantum well microstructured by growth on a submicron grating

We report on the transport properties of quantum wire-like GaAs/AlGaAs heterostructures, obtained by organometallic chemical vapor deposition of a modulation-doped quantum well structure on a submicron grating, etched in the substrate prior to growth. Shubnikov–deHaas and mobility measurements show that the electron gas is preserved in the grating areas and that transport parallel to the grating is not severely degraded as compared to an unpatterned control sample. Perpendicular to the grating the mobility strongly decreases at low temperatures, leading to an anisotropy ratio of 1:200. The temperature dependence of the perpendicular mobility indicates strong boundary scattering at the GaAs/AlGaAs interfaces.

InGaAs metal-semiconductor-metal photodetectors for long wavelength optical communications

A review is presented of the properties of interdigitated metal-semiconductor-metal (MSM) Schottky barrier photodetectors based on the InGaAs-InP material system, and the performance achieved by experimental devices is discussed. The experimental work concentrates on the barrier-enhanced lattice-matched InAlAs-InGaAs device grown by low pressure organometallic chemical vapor deposition (OMCVD), which has to date yielded detectors with the highest performance characteristics. Current research on their integration with FETs to form monolithic receivers and with waveguides for on-chip optical signal processing is also included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The growth of GaInAs/InP and GaInAs/AlInAs superlattices with thin barrier layers by low pressure organometallic chemical vapor deposition

In this paper we show that the growth of InP/GaInAs superlattices with thin (⩽ 3 nm) InP barrier layers is not possible when the surface migration rates of the group III species are large. Large migration rates lead to growth predominantly by lateral motion of steps, due to nucleation at step or kink sites, and therefore to the creation of macro-steps in the InP layer. The planarity of the layers constituting the superlattice is, therefore, lost, with the effect being amplified as the growth proceeds. This effect can be minimized by the use of low growth temperature, high group V flows, high, growth rates, halts after InP growth, a substrate oriented as close to (100) as possible, and by ensuring thickness uniformity across the substrate. The macro-step formation is approximately parallel to [01 1 ], implying that either the surface migration rate or the ratio of the lateral growth velocities, υ InPon InGaAs/υ InPon InP, is maximum along [011]. A similar thickness limitation does not appear to exist for GaInAs, with superlattices containing 1 nm thick GaInAs layers being easily grown. Furthermore, the problems encountered in the growth of InP/GaInAs superlattices were not present in the growth of AlInAs/GaInAs superlattices with similar layer thicknesses. Finally, it is shown that 100 period (2.5 nm InP/2.5 nm GaInAs) nearly defect free superlattices, with excellent surface morphology, can be grown if the migration rates of the group III species are reduced, substrates oriented close to (100) are used, and thick (40–50 nm) InP layers are introduced every 10 periods.

Single-source organometallic chemical vapour deposition process for sulphide thin films: Introduction of a new organometallic precursor Bu nIn(SPr i) 2 and preparation of In 2S 3 thin films

Single-source organometallic chemical vapour deposition was successfully introduced using Bu n In(SPr i ) 2 as a precursor molecule and tetragonal β-In 2S 3 thin layers with a strongly preferred (103) growth orientation were obtained on Si(111) and quartz substrates at a substrate temperature T sub of 300–400°C. A dependence of growth rate that lay between 25 and 450 nm h −1 on source temperature T source (60–80 °C) and on T sub was observed. β-In 2S 3 thin films thus obtained were photoresponsive, with optical band gap energies and dark conductivity estimated as 1.98 eV and 2.0 × 10 −4 S cm −1 respectively. Furthermore, a polycrystalline In 6S 7 layer, which is one of the sulphur-deficient phases of indium sulphide, was grown when T sub was raised to 450°C in the same single-source system.