Horizontal Metalorganic Chemical Vapor Deposition Research Articles

Mobility enhancement and yellow luminescence in Si-doped GaN grown by metalorganic chemical vapor deposition technique

We have studied the Si-doping characteristics in GaN on (0 0 · 1) sapphire substrates. The films were grown by horizontal metalorganic chemical vapor deposition technique at 100 Torr. Prior to Si-doping, achievement of optimum growth conditions was preceded in order to insure doping controllability. For undoped film, background carrier concentration was as low as 4 × 10 17cm −3. 10 K-photoluminescence (PL) in undoped film was dominated by the luminescence from two sharp free-excitons and one bound-exciton. n-Type doping with SiH 4 was carried out and electron concentration of up to 2 × 10 19cm −3 was achieved. As the electron concentration increased, the activation efficiency of Si donor also increased. In spite of the increased carrier concentration, Hall mobility in the doped films was increased by a factor of up to two (220 cm 2/V s) compared to the undoped films. The mobility behavior is attributed to a transport mechanism involving defect band conduction and does not correlate with the line width of the X-ray rocking curve. In addition, as the doping concentration increased, yellow luminescence occurring at around 2.2 eV gradually dominated PL spectra at 10 K and room temperature. Our PL study suggests that gallium vacancy is responsible for the yellow luminescence.

Basic studies of gallium nitride growth on sapphire by metalorganic chemical vapor deposition and optical properties of deposited layers

We have studied the growth of gallium nitride on c-plane sapphire substrates. The layers were grown in a horizontal metalorganic chemical vapor deposition reactor at atmospheric pressure using trimethylgallium (TMG) and ammonia (NH3). Variation of the V/III ratio (150–2500) shows a distinct effect on the growth rate. With decreasing V/III ratio, we find an increasing growth rate. Variation of the growth temperature (700–1000°C) shows a weak increase in growth rate with temperature. Furthermore, we performed secondary ion mass spectroscopy measurements and find an increasing carbon incorporation in the GaN films with decreasing ammonia partial pressure and a growing accumulation of carbon at the substrate interface. Photoluminescence measurements show that samples with high carbon content show a strong yellow luminescence peaking at 2.2 eV and a near band gap emission at 3.31 eV. With increasing carbon content, the intensity of the 3.31 eV line increases suggesting that a carbon related center is involved.

Deposition of AlN at lower temperatures by atmospheric metalorganic chemical vapor deposition using dimethylethylamine alane and ammonia

We have studied an atomic layer growth process using amine–alane adducts as precursors for depositing aluminum nitride (AlN) thin films at temperatures between 300 and 800 K. The atomic layer deposition process was carried out in a horizontal metalorganic chemical vapor deposition (MOCVD) reactor at atmospheric pressure using H2 as a carrier gas. Dimethylethylamine alane [(CH3)2(C2H5)N:AlH3] and ammonia (NH3) were used as source gases and sequentially flowed into the reactor with a hydrogen flush between each source gas step. Thin films were deposited onto Si(001) and Al2O3(0001) substrates that were heated on a susceptor by radio frequency induction. Analysis by x-ray photoelectron spectroscopy and x-ray diffractometry revealed deposition of AlN at temperatures as low as 613 K. Processing at lower temperature (510 K) resulted in no detectable AlN deposition while processing at higher temperature (783 K) resulted in nitridation of the Si(001) surface to Si3N4 but no detectable AlN deposition on Si(001) or Al2O3(0001).

Magnesium Doping of GaN by Metalorganic Chemical Vapor Deposition

ABSTRACTP-type GaN films were grown on sapphire substrates in a horizontal metalorganic chemical vapor deposition system using (C5H5)2Mg (Cp2Mg) as the p-dopant source. It is found that the acceptor concentration in the post-growth annealed GaN samples increases with the Mg flow rate and reaches a peak value of 1×1019 cm−3 at Mg flow rate of 0.84 ĉmol/min. The films remain semi-insulating even after annealing when the Mg flow rate is higher than 1.08 ĉmol/min. The effects of annealing temperature and duration on the electrical properties of GaN are also investigated. The results confirm that a 800 °C, 30 minutes post-growth annealing in N2 ambient is sufficient to activate most of the Mg atoms. In addition, study of rapid thermal annealing of Mg-doped GaN was carried out and the results show that the p-type acceptor concentration obtained is comparable to the results obtained using furnace annealing process. Finally, GaN light emitting diodes (LEDs) are demonstrated using undoped layer as the n-type base layer in a p-on-n structure. The light emission spectra are dominated by the 430 nm peak, accompanied with two relatively weak peaks located at 380nm and 550nm.

The onset of transverse recirculations during flow of gases in horizontal ducts with differentially heated lower walls

A computational study has been performed to identify the onset of transverse buoyancy-driven recirculations during laminar flow of hydrogen and nitrogen in horizontal ducts with cool upper walls, and lower walls consisting of three sections: a cool upstream section, a heated middle section and a cool downstream section. The motivation for this work stems from the need to identify operating conditions maximizing the thickness uniformity, the interface abruptness and the precursor utilization during growth of thin films and multi-layer structures of semiconductors by metalorganic chemical vapour deposition (MOCVD). A mathematical model describing the flow and heat transfer along the vertical midplane of MOCVD reactors with the above geometry has been developed and computer simulations were performed for a variety of operating conditions using the Galerkin finite-element method. At atmospheric pressure and low inlet velocities, transverse recirculations form near the upstream and downstream edges of the heated section. These can be suppressed either by increasing the inlet velocity of the gas, so that forced convection dominates natural convection, or by decreasing the operating pressure to reduce the effects of buoyancy. The onset of transverse recirculations has been determined for Grashof (Gr) and Reynolds (Re) numbers covering the following ranges: 10−3 < Re < 100 and 1 < Gr < 106, with Gr and Re computed using fluid properties at the inlet conditions. The computations indicate that, for abrupt temperature changes along the lower wall (worst-case scenario), transverse recirculations are always absent if the following criteria are satisfied: \[(Gr/Re) < 100\quad {\rm for}\quad 10^{-3} < Re \leqslant 4\quad {\rm and}\quad (Gr/Re^2) < 25\quad {\rm for}\quad 4 \leqslant Re < 100.\]The predicted critical values of Re, which correspond to the onset of transverse recirculations, agree well with reported experimental observations. The above criteria can be used for optimal design and operation of horizontal MOCVD reactors and may also be useful for heat transfer studies in horizontal ducts with differentially heated lower walls.

The deposition of BaFe12O19 by metalorganic chemical vapor deposition

We report the first successful use of metalorganic chemical vapor deposition (MOCVD) in the fabrication of ferromagnetic oxide thin films. A substituted acetylacetonate barium complex has been used with ferrocene in a horizontal hot wall MOCVD system to deposit both polycrystalline and c-axis preferred films of BaFe12O19. These films were examined for crystallinity, morphology, composition, and magnetic properties. Their magnetic properties were found to be consistent with films prepared by other techniques.

Effet des paramètres de croissance sur les couches épitaxiales d'InP obtenues par MOCVD (metal-organic chemical vapor deposition) à basse pression

The development of a low pressure, horizontal MOCVD (metal-organic chemical vapour deposition) reactor has allowed us to study the effect of phosphine and trimethylindium molar fluxes on the epitaxial growth of InP. Study of the growth rate in the temperature range 550–620 °C shows that the growth can be limited by the reaction kinetics at the surface. Epitaxial layers of good morphological quality have been obtained by reducing the rate of growth even if the growth is limited by the reaction kinetics at the surface. The variation of the electronic mobility with the PH3 molar flux reveals the existence of an optimum mobility region, even with a constant V: III ratio. Photoluminescence experiments carried out on the samples show the good crystallographic quality of the epitaxial layers. Spectra taken in the energy range 0.8–1.2 eV show the evolution of two structures at 0.91 and 1.08 eV that we associate with an antisite PIn and a VIn defect, respectively.[Journal translation]

Characterization of MOCVD fluid dynamics by laser velocimetry

The process of metalorganic chemical vapor deposition (MOCVD) is critically dependent on the fluid dynamics of the reacting and carrier gases. Quantitative understanding of the basic fluid dynamics associated with a reactor design is central to the application of engineering techniques to achieve design improvements in efficiency, bulk production and growth uniformity. A laser velocimetry (LV) system has been adapted specifically to acquire such quantitative information for the low Reynolds number mixed convective flows commonly encountered in MOCVD reactors. The instrument uses three color-separated wavelengths of an argon-ion laser to make three simultaneous independent orthogonal measurements of the flow field at specified interior locations. The technique is noninvasive, provides high spatial resolution, and is compatible with reactors operating at growth temperatures. The fluid dynamics of a horizontal MOCVD reactor used for GaAs growth were characterized by laser velocimetry measurements. The full three-component LV system was employed to determine a three-dimensional map of the flow field inside the quartz reactor vessel. Data have been obtained from the vessel both at room temperature and heated to growth temperature by RF induction. The two cases were compared to evaluate the effects of gravity-induced convection and buoyancy. Significant convective effects were found in the heated reactor, while fluidic switching effects were observed during room temperature operation. Instrumentation details and flow field measurements are presented.

Large-area HgTe–CdTe superlattices and Hg1−xCdxTe multilayers on GaAs and sapphire substrates grown by low-temperature metalorganic chemical vapor deposition

Specular HgTe–CdTe superlattice epilayers have been obtained on two 2-in. diam GaAs or sapphire wafers per growth run using a horizontal metalorganic chemical vapor deposition (MOCVD) reactor in which the pyrolysis of the organometallics is induced by a cracking susceptor suspended above the substrates. This enables growth of superlattices below 300 °C using the standard precursors dimethyl cadmium, diethyl telluride, and elemental mercury. Annealing the superlattices at 350 °C converts them to homogeneous Hg1−xCdxTe. Compositional profiles obtained by Rutherford backscattering, sputter Auger depth profiling, and e-beam analysis of ultramicrotomed thin cross sections, were used to study interdiffusion of the CdTe and HgTe layers during growth and annealing. Arrays of metal–semiconductor field effect transistors (MESFETS) and photoconductive detectors with room temperature peak responsivity between 1.3 and 1.6 μm have been prepared from incompletely interdiffused material grown on semi-insulating GaAs without thick buffer layers. Device processing used mesa technology and a KI:I2:HBr etchant developed for its selectivity with respect to Hg1−xCdxTe . Capping layers of CdTe and HgTe deposited at low temperatures have been investigated as dielectric and ohmic contacts, respectively. Electrical analyses by Hall and C–V measurements are presented. Room temperature electron mobilities up to 27 500 cm2 /V s and resistivities of 1–2 Ω cm have been observed for the HgTe layers. Information on crystallinity and defect structure of the epilayers was obtained by selected area electron channeling patterns, high-resolution transmission electron microscopy (HRTEM), Rutherford backscattering spectroscopy (RBS) and four-circle, double-crystal, and triple-crystal x-ray diffraction. Compositional profiles in the 100 cm2 deposition area were obtained by wavelength dispersive x-ray analysis (WDX), Fourier transform infrared (FTIR) spectrometry and inductively coupled plasma atomic emission spectrometry (ICPAES).