L.J. Giling

Growth of {100} textured diamond films by the addition of nitrogen

Localized {100} fiber textured diamond films were grown by addition of 20–200 ppm nitrogen into the gas phase during hot‐filament chemical‐vapor deposition (CVD). Cathodoluminescence indicates the presence of the nitrogen‐vacancy system in the {100} textured diamond, whereas a blue ‘‘band A’’ luminescence is normally observed in diamond films grown without nitrogen addition. The results demonstrate that the nature of the substrates used for growth has no appreciable influence on the {100} texture, which implies that this fiber texture is obtained by competitive growth and selection of facets. The interaction of nitrogen with the {100} surface is a highly important factor in this process. Homoepitaxial growth shows that the addition of a small amount of nitrogen greatly enhances the growth rate of the {100} faces, making 〈100〉 the fastest growth direction in comparison with the 〈110〉 and 〈111〉 directions. This is attributed to breaking of a part of the dimers on the (2×1) reconstructed {100} surface by nit...

Return flows in horizontal MOCVD reactors studied with the use of TiO2 particle injection and numerical calculations

Flow visualization experiments with the use of TiO2 particles were performed for a horizontal MOCVD reactor which was resistance-heated from below and water-cooled on top. It is shown that, due to the heating of the incoming gas, very pronounced return flows can occur at the leading edge of the heated susceptor. The formation of these return flows was systematically studied as a function of pressure, flow velocity and temperature. We show that for typical flow rates, carrier gases and reactor design used in MOCVD growth of GaAs and AlGaAs, it is possible to avoid return flows by decreasing the pressure to about 0.2×105 Pa. Besides these experimental studies also numerical calculations on gas flows based on the differential equations for the conservation of mass, energy and momentum were performed, using a two-dimensional finite difference procedure. Parameters in this study were again pressure, flow velocity and temperature, and in addition also the height of the reactor and the type of carrier gas were varied. In comparing the results obtained by the flow simulation experiments and the numerical calculations, it is found that the occurrence of return flows is predicted accurately by the numerical flow calculations. Small differences can be ascribed to three dimensional effects which are not included in the 2D numerical calculations. Both flow visualization experiments and numerical calculations show that the occurrence of return flows is mainly determined by only two dimensionless hydrodynamic numbers: the Grashoff number Gr and the Reynolds number Re. It is possible to define a number αcrit such that no return flow occurs for GrReκ<αcrit. Here κ equals 1 for small Reynolds numbers (Re ≤ 4) and goes to 2 for larger Reynolds numbers (Re ≥ 8), being independent of all other hydrodynamic parameters. The critical value αcrit was found to depend slightly on the temperature difference and is independent of all other parameters. The criterion is confirmed by both the TiO2 experiments and the numerical calculations for 0.1 < Re < 10 and 10 < Gr < 10 000.

Growth and etching of silicon in chemical vapour deposition systems; The influence of thermal diffusion and temperature gradient

Abstract In the growth of epitaxial silicon using SiCl4 as source material it is known, that the growth rate at first increases with increasing pSiCl4, but at higher pSiCl4 decreases and finally becomes negative. The exact shape of the growth curve and especi ally the point of zero growth, where the etch rate counterbalances the growth rate, differs considerably amongst various investigators. This phenomenon was subject to theoretical considerations. Three models were evaluated: (i) a simple equilibrium model in which gas transport limited kinetics are used with one single diffusion coefficient for all species; (ii) an extended model using individual diffusion coefficients; (iii) a model as in (ii) but including the effect of thermal diffusion. It is shown that models (i) and (ii) do not give a general solution of the problem. The best results are obtained with model (iii). The growth rate appears to be very sensitive to the temperature gradient ▽T. As ▽T depends on the kind of apparatus used in the deposition process, it provides a reasonable explanation for the observed differences.

CVD DIAMOND GROWTH MECHANISMS AS IDENTIFIED BY SURFACE-TOPOGRAPHY

Abstract The surface morphologies of numerous homoepitaxial, chemical-vapour-deposition-grown diamond films have been examined by phase-sensitive optical microscopy. The layers were produced by the hot filament technique as well as by the acetylene-oxygen combustion method. The {111} and {100} faces manifest themselves as F faces below the roughening temperature and grow via steps nucleated at three-dimensional diamond particles or at dislocations. The rate-determining step in {111} diamond growth is a hindered surface diffusion of the growth species towards the steps. The layer-by-layer growth on the 100 faces is discussed in terms of (2 × 1) surface reconstruction in combination with the presence of a 41 screw axis. The {113} face on flame-grown diamonds is made up of strong 〈110〉 chains of bonds which are interconnected by weak forces due to surface reconstruction. The slight curvature of this face points to an F face close to the roughening point. The {110} face is rough, i.e. K/S type, and no layer growth occurs. The different modes of crystal growth as well as local differences in step spacing are replicated as variations in the intensity of band A and 575 nm cathodoluminescence.

Controlled deposition of diamond from an acetylene-oxygen combustion flame

Abstract An experimental set-up for the deposition of diamond by an acetylene-oxygen combustion flame was developed in which it is possible to control the deposition temperature within 10°C during long-term experiments. This degree of accuracy is obtained by cooling the back of the substrate holder with an electronically controlled water injection system and using soldered substrates, ensuring a good thermal contact. With this set-up a large number of experiments were performed with deposition times of 1 h. Special attention was given to the growth of diamond layers with uniform thickness and morphology because these properties are considered essential for future applications. It was found that the deposition temperature, the total gas flow, the composition of the gas phase and the position of the substrate in the flame all have major influences on the deposit. Not only the growth rate and the quality of the diamond are strongly influenced by the deposition conditions, but also the preferred crystal habit and the homogeneity.

Electrical conduction in homoepitaxial, boron-doped diamond films

Epitaxial, boron-doped diamond films were grown by hot-filament-assisted chemical vapour deposition (CVD) on (100) and (110) natural diamond substrates. Resistivity measurements for 10 K<T<500 K showed a clear transition from band to hopping conduction upon lowering of temperature. In the band conduction regime, the (100) films had higher conductivity than the (110) samples. The reverse was found in the hopping regime. This is explained by the difference in crystal growth mechanisms, leading to higher boron concentrations and lower carrier mobilities for (110) samples than for (100) oriented films. Hall effect measurements were performed for the most lightly doped (100) film at a boron level of 2.7*1018 cm-3 in the band conduction region up to 750 K. A mobility maximum of mu H=590 cm2 V-1 s-1 at 295 K was found, and the compensation ratio was determined to be smaller than 0.02. Some preliminary values for the Hall effective mass of valence band holes are given.

Characterization of single-crystal diamond grown by chemical vapour deposition processes

Abstract Homoepitaxial diamond films have been deposited on natural diamond substrates by the hot-filament-assisted chemical vapour deposition technique and by the oxygen-acetylene combustion flame method. From the surface microtopographic, the fractographic and especially the spectroscopic characterization of these films it was observed that the crystallographic orientation of the substrate is an important factor for the quality of the epilayer. The incorporation of point defects such as boron, hydrogen and nitrogen is strongly dependent on both the substrate orientation and the deposition temperature. The best results were obtained for epilayers grown by the combustion flame on {100} substrates.

Influence of growth parameters on the incorporation of residual impurities in GaAs grown by metalorganic chemical vapor deposition

The incorporation of impurities in GaAs epitaxial layers grown from trimethyl gallium (TMG) and AsH3 has been studied in detail by varying a large number of growth parameters. These include the V/III ratio, temperature, the axial position in the reactor, gas sources, substrate and susceptor material, carrier gas, substrate misorientation, and the crystallographic orientation of the substrate. As main characterization techniques photoluminescence and Hall–van der Pauw measurements have been used. Donor and acceptor concentrations in the layers have been found to vary not only with temperature and V/III ratio, but also with the axial position in the reactor, giving rise to p/n transitions and maxima in the carrier mobility. The V/III ratio is shown to be effectively constant for larger axial distances in the cell. Highly doped substrates have been found to give rise to outdiffusion of defect complexes into the layers. The main acceptor impurities found in this work are zinc, silicon, and carbon. They are sh...

On the formation of antiphase domains in the system of GaAs on Ge

The formation of antiphase domains (APDs) in GaAs grown on Ge(001) misoriented towards 〈110〉 has been studied as a function of substrate misorientation angle, growth rate, VIII ratio and growth temperature, by DSL (diluted Sirtl-like etchant used with light) and molten KOH defect revealing etch; transmission electron microscopy and optical interference contrast microscopy. Strong dependencies of the formation of APDs on all the parameters investigated have been found, which provides detailed information on the characteristics of polar on nonpolar heteroepitaxy. Insight into the mechanism of APD formation leads to a concept to grow completely APD-free GaAs on Ge, which has been proved by the experimental results of this study.

Rapid single crystalline diamond growth by acetylene-oxygen flame deposition

Abstract Single crystal diamond layers, up to 150 μm in thickness, have been deposited on {110} natural diamond substrates from an acetylene-oxygen flame. The diamond was characterized by X-ray diffraction, Raman and other optical spectroscopic techniques. Although the rate of deposition was high (50 μm/h), material of good crystalline quality was obtained. Infrared absorption spectroscopy established hydrogen as a main impurity in the crystals. The photoluminescence spectrum was dominated by well known nitrogen-vacancy centres with zero phonon lines at 575 and 638 nm.