J.J. Schermer

CVD diamond deposition on steel using arc-plated chromium nitride interlayers

This paper reports on hot filament CVD diamond deposition onto steel using arc-plated chromium nitride (CrN) as the interlayer. Direct deposition of diamond onto steel leads to the formation of a non-adhering layer of graphitic soot covered by poor-quality diamond. However, if arc-plated CrN coatings with a thickness of 2.5 μm are used, diamond formation takes place. Adherent and good-quality diamond coatings are obtained after several hours of deposition at a substrate temperature as low as 650 °C. Micro-Raman spectroscopy, scanning electron microscopy, X-ray diffraction and EDAX analysis have been employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers and the modified substrate interlayers. The Scotch tape test is used to assess the adhesion of the diamond coatings.

Effects of nitrogen impurities on the CVD growth of diamond: step bunching in theory and experiment

Abstract The step flow dynamics during homoepitaxial diamond deposition on vicinal {001} diamond surfaces in the presence of nitrogen impurities in the gas phase is investigated by experiments as well as by computer simulations. The adsorption of impurities on the diamond surfaces leads to step bunching, whereby complex two-dimensional patterns are formed. A mesoscopic Monte Carlo model is used to study this effect, whereby line tension, anisotropy in step propagation, roughness of steps and impurity strength are introduced on a physical basis. The similarity between experimental results and the step configurations resulting from simulations is remarkable. Furthermore, the coexistence of both step bunching and an increased growth rate upon nitrogen addition is explained by the fact that nitrogen on the surface has a different effect on the diamond growth than sub-surface nitrogen. This study gives a demonstration of a fruitful co-operation between computer simulations and real world experiments, which leads to a better understanding of the physical processes occurring during crystal growth.

Etching AlAs with HF for Epitaxial Lift-Off Applications

The epitaxial lift- off process allows the separation of a thin layer of III/ V material from the substrate by selective etching of an intermediate AlAs layer with HF. In a theory proposed for this process, it was assumed that for every mole of AlAs dissolved three moles of H-2 gas are formed. In order to verify this assumption the reaction mechanism and stoichiometry were investigated in the present work. The solid, solution and gaseous reaction products of the etch process have been examined by a number of techniques. It was found that aluminum fluoride is formed, both in the solid form as well as in solution. Furthermore, instead of H-2 arsine (AsH3) is formed in the etch process. Some oxygen- related arsenic compounds like AsO, AsOH, and AsO2 have also been detected with gas chromatography/ mass spectroscopy. The presence of oxygen in the etching environment accelerates the etching process, while a total absence of oxygen resulted in the process coming to a premature halt. It is argued that, in the absence of oxygen, the etching surface is stabilized, possibly by the sparingly soluble AlF3 or by solid arsenic

HF Species and Dissolved Oxygen on the Epitaxial Lift-Off Process of GaAs Using AlAsP Release Layers

The lateral etch rate of the epitaxial lift-off (ELO) process was determined as a function of the total HF concentration Cup and the O 2 partial pressure Po 2 . For this purpose samples were grown by metallorganic chemical vapor deposition and etched using a weight-induced ELO process. It was found that the etch rate increases linearly with C HF , which is in accordance with the model on the ELO process presented in a previous paper. This result and composition calculations of HF solutions show that the first step in the etch process of AlAs with an HF solution most probably takes place by chemical attack of undissociated HF on AlAs surface bonds. Furthermore, it is shown that the ELO rate increases slightly over a Po 2 range varying from 0.046 to 0.98 atm and that for Po 2 = 0.003 atm, a significantly lower etch rate is found. We suggest that the observed decrease is the result of surface passivation by elemental arsenic, which is formed by the reaction of AlAs with H + . An oxygen-poor atmosphere may allow the build-up of elemental arsenic on the surface, thus slowing down the AlAs reaction with HF. Oxygen, by removing arsenic as As 2 O 3 , keeps the surface active.

Relation between gas phase CN radical distributions, nitrogen incorporation, and growth rate in flame deposition of diamond

Controlled amounts of nitrogen were added during oxyacetylene flame deposition of diamond to investigate the possible role of the CN radical in the effects of nitrogen addition. CN radical distributions were visualized using two-dimensional laser induced fluorescence (LIF) and compared with nitrogen incorporation into the layer and with the diamond growth rate, which were measured by means of cathodoluminescence (CL) and optical microscopy, respectively. For the studied range of nitrogen flows, it was found that the CN LIF signal in the center of the flame is linearly dependent on the added amount of nitrogen. Diamond deposition in the central region is mainly influenced by the deposition parameters, whereas deposition in the outer zone is largely determined by the interaction of the flame with the ambient; the annulus of enhanced growth is affected by both the deposition parameters and the ambient. By a simple consideration, in which the growth rate is separated in nitrogen dependent and independent cont...

Structure and morphology of epitaxial PbZrO3 films grown by metalorganic chemical vapor deposition

PbZrO3 (PZ) films of different thicknesses have been grown by metalorganic chemical vapor deposition on SrTiO3 (STO) substrates. The structure of the films was determined by x-ray diffraction and transmission electron microscopy. At the deposition temperature, the growth is cube on cube and is therefore heteroepitaxial. During cool down, PZ goes through a phase transformation from paraelectric to antiferroelectric at the Curie temperature and its cubic structure is stretched to orthorhombic. This results in domain formation in the PZ films corresponding to the different stretching directions. At room temperature, the thin PZ film consists of at least two different (120) domain variants and the thin-film–substrate relation can be described as (120)[002]PZ//(100) [001] STO for one of these variants. By etching down a thick film, it was observed that ∼260 nm is the threshold thickness, above which two additional different (002) domain variants appear in addition to the (120) domain variants. For one of the ...

The effect of nitriding on the diamond film characteristics on chromium substrates

Abstract In this report, we present a study of diamond deposition on pure and nitrided chromium substrates using the hot filament-assisted chemical vapour deposition technique. Deposition was performed at substrate temperatures varying from 475 to 750 °C for different exposure times. Scanning electron microscopy (SEM), micro-Raman spectroscopy and X-ray diffraction (XRD) techniques were employed to study the modified interlayers and diamond films. The high solubility and diffusivity of carbon in pure chromium result in an increased incubation time for diamond nucleation. However, even a 4–5-μm-thick nitrided layer is efficient as a diamond-nucleating surface, with a reduced incubation time as compared to pure chromium. Fully covering and adhering diamond films were obtained on the nitrided Cr specimens at temperatures between 550 and 750 °C. As a result of the nitriding process, the nitride diffusion layer reduces the carbon solubility at the substrate surface, thereby reducing the incubation time for diamond nucleation. Due to the strong chemical and mechanical bonding of the diamond films to the nitrided Cr substrates, the residual compressive stresses are accommodated, leading to adherent, continuous diamond films. The present study, however, also indicates an optimal low-temperature deposition condition to obtain a continuous diamond film directly on pure Cr.

Chemical vapour deposition of diamond on nitrided chromium using an oxyacetylene flame

Abstract In this paper we present our first preliminary results on chemical vapour deposition (CVD) of diamond onto nitrided chromium using an oxyacetylene flame. Polycrystalline diamond films were obtained after deposition at very low substrate temperatures (

Study of wet chemical etching of AlxGa1-xInP2 films using hydrochloric acid

The etching behavior of Al x Ga 1-x InP 2 (0 ≤ x ≤ 1) in aqueous HCl was investigated for layers on their native GaAs substrates as well as for layers after releasing from their substrate and transferring to a foreign plastic carrier utilizing the epitaxial lift-off (ELO) technique. For InGaP 2 layers on their native substrates the activation energy of the etching rate was determined to be 22 kcal/mol for HCl concentrations of both 6 and 12 M. The surface roughness of the partially etched Al x Ga 1-x InP 2 layers as determined with atomic force microscopy (AFM) was found to decrease with increasing aluminum fraction and to be smaller for 6 M than for 12 M HCl. Al x Ga 1-x InP 2 layers on foreign plastic carriers were often found to be not etched in HCl, in contrast to layers on substrates. This could not be attributed to a single cause and it is suggested that the nonetching behavior is related to a combination of factors, like exposure of the layers to the ELO process and strain induced by the foreign carrier. AFM studies showed an increased density of irregularities at the surfaces of the Al x Ga 1-x InP 2 samples that later showed nonetching behavior.

The effects of nitrogen addition on flame deposition of diamond

The influence of nitrogen addition on oxyacetylene flame deposition of diamond has been investigated by controlled addition of nitrogen to the combustion gases. Heretofor, the nitrogen incorporation into the diamond layer, the growth rate, and the diamond morphology were determined as a function of the nitrogen flow and compared to gas-phase distributions of the CN radical close to the deposition substrate. Two-dimensional laser induced fluorescence (LIF) was applied for the gas-phase measurements: cathodoluminescence (CL), scanning electron microscopy (SEM), and optical microscopy were used for the determination of the nitrogen incorporation, morphology and growth rate, respectively. In the studied range of nitrogen flows, a linear relation was observed between the added amount of nitrogen and the CN LIF signal in the center of the flame. It was found that that diamond deposition in the central region is largely influenced by the deposition parameters, whereas deposition in the outer zone depends mainly on the interaction with the ambient air: the annulus of enhanced growth marks the transition between those areas. In the central area, a correlation was observed between the onset of quenching of the CL signal and the occurrence of secondary nucleation on the diamond {111} facets. The observation that both the CN LIF signal and the nitrogen incorporation in the central region increase with the added amount of nitrogen indicates, together with the changes in central growth rate and morphology that are observed upon nitrogen addition, that CN or a closely related species plays an important role in the influence of nitrogen addition on flame deposition of diamond.