Monocrystalline Substrates Research Articles

Structure, morphology and optical properties of CuInS 2 thin films prepared by modulated flux deposition

The structure, morphology and optical properties of copper indium sulfide thin films prepared by a novel modulated flux deposition procedure have been investigated for layers from 200 to 400 nm thickness. These polycrystalline CuInS 2 films grown onto glass substrates showed CuAu-like structure, similar to epitaxial CuInS 2 films grown onto monocrystalline substrates, and direct band gap values Eg=1.52–1.55 eV, optimum for single-junction photovoltaic applications. The increase in the layer thickness leads to growth of the average crystallite size and increases slightly the surface roughness and the absorption coefficient.

Off lattice Monte Carlo simulation study for different metal adlayers onto (1 1 1) substrates

The structure, energetics, and elastic properties of metallic adlayers adsorbed onto monocrystalline substrate surfaces are analyzed for a set of systems of electrochemical interest. The systems considered involve Ag, Au, Pt, Pd, and Cu. The different adsorbate/substrate (1 1 1) systems were simulated employing off lattice Monte Carlo simulations with embedded atom method potentials in the canonical ensemble at 300 K. The underpotential and overpotential deposition trends observed for this set of transition metal systems are analyzed taking into account the structure of the monolayer, the energy of the systems, and the surface stress change.

Effects of growth temperature on the surface morphology of silicon thin films on (111) silicon monocrystalline substrate by liquid phase epitaxy

Abstract We investigated the effects of growth temperature on the surface morphology of silicon layers grown by liquid phase epitaxy method on a (1 1 1) oriented silicon substrate in a relatively low-temperature range from 600°C to 900°C using Au–Bi alloy solvent. Layers are formed in the following growth sequence: (1) commencing in the form of initial nuclei as starting points of growth, (2) these structures grow along lateral and vertical directions as island structures, and (3) coalesce each other. Moreover, it was made clear that flat layers tend to cover the substrate completely at high growth temperature, in order to clarify the main factor that influences the surface morphology, an empirical model of the growth process was constructed. As a result, the temperature dependence of the surface morphology mainly depends on the temperature dependence of the preferential growth direction of Si on Si (1 1 1).

Metal-organic chemical vapour deposition of mixed-conducting perovskite oxide layers on monocrystalline and porous ceramic substrates

Perovskite oxide layers, i.e. manganites La 1− x (Sr,Ca) x MnO 3, ferrates La 1− x Sr x Fe 1− y Co y O 3, gallates La 1− x Sr x Ga 1− y (Co,Ni,Fe) y O 3 of a thickness of 0.8–2 μm, were deposited by pulsed injection MOCVD (metal-organic chemical vapour deposition) on various monocrystalline and porous ceramic substrates. The layers were characterised by X-ray diffraction, scanning electron microscopy, wavelength dispersion spectroscopy and by electrical measurements of the total conductivity vs. temperature. Such oxides are known as mixed electronic–ionic conductors and are largely studied as materials for the fabrication of oxygen permeable membranes. One of the aims of this work was to estimate the suitability of the pulsed injection MOCVD technique for the preparation of dense perovskite layers for their use as membranes for oxygen.

Magnetization of EuS–PbS Multilayers with Antiferromagnetic Interlayer Coupling

SQUID magnetometry is applied to study the temperature and magnetic field dependence of magnetization M(T, H) of semiconductor EuS–PbS ferromagnetic multilayers grown on insulating KCl(100) and conducting n-PbS(100) monocrystalline substrates. For low external magnetic fields (of the order of 10 Oe) and PbS spacer layers thinner than about 2 nm, we observe in EuS–PbS–EuS trilayers the strongly nonmonotonic temperature dependence of magnetization with almost zero total magnetic moment below the Curie temperature. The application of the magnetic field of the order of 100 Oe restores the regular monotonic increase of magnetization with decreasing temperature. To explain this M(T,H) dependence we present a model that considers the competition of three (temperature dependent) contributions to the total magnetic energy of the trilayer: the antiferromagnetic interlayer interaction energy, the Zeeman energy, and the energy of in-plane magnetocrystalline anisotropy.

Evidence of hetero-epitaxy of Sm-orthoferrite on MgO(0 0 1) substrates by the pulsed laser deposition technique

Thin films of SmFeO 3 have been prepared by the pulsed laser deposition technique on MgO(0 0 1) mono-crystalline substrates. The growth of SmFeO 3 on MgO(0 0 1) substrate has been studied by X-ray diffraction (XRD) and by reflection high-energy electron diffraction (RHEED). Hetero-epitaxial growth of SmFeO 3(1 1 0) is evidenced with lattice parameters closed to the bulk orthorhombic values: 〈a〉=〈b〉≅d 110 2 =0.5567 nm from XRD and c=0.78 nm from RHEED. The epitaxial relation found is: the [0 0 1] and [1 1 ̄ 0] directions of the SmFeO 3 are collinear to the equivalent [1 0 0] or [0 1 0] orientations of the MgO as confirmed by a pole figure deduced from electron back-scattering diffraction. The polycrystalline Sm-orthoferrite outgrowth is estimated to be approximately 1%.

Silicon sheet from silane: first results

A process to obtain self-supported thin silicon films is being developed. Films are grown by optical chemical vapour deposition (CVD) (using halogen lamps as heating system) from silane, at low temperature and relatively high growth rates, on silicon substrates with a sacrificial layer of porous Si (PS), which allows film detachment. The PS layer was formed by anodisation of the Si-substrate surface in a HF:ethanol solution. Film deposition was carried out in an optical cold wall horizontal CVD reactor, operating at atmospheric pressure, and specially designed for this study. Deposition rates and film morphology were studied as a function of substrate nominal temperature, gas concentration and flux. In the final chosen conditions, deposition occurs at a nominal temperature of 840°C, with a silicon growth rate between 2 and 4 μm/min, which is relatively high for the low temperature used. A good usage of silane gas was already achieved, with 80–85% of the silicon in the silane gas being deposited on a 40×40 mm 2 substrate, with very low deposition rate on the reactor wall. Films of thicknesses from 10 to 150 μm were deposited. The films were found to be continuous with surfaces coated with whiskers. Film detachment from multicrystalline substrates has proved unsuccessful so far, while it readily occurs when monocrystalline substrates are used. The reason for this is macropore collapse and film rupture, usually occurring in the smaller grain regions of the multicrystalline substrates.

Pulsed liquid-injection metalorganic chemical vapor deposition of (La0.7Sr0.3MnO3/SrTiO3)15 superlattices

( La 0.7 Sr 0.3 MnO 3 / SrTiO 3 ) 15 superlattices have been grown by pulsed liquid-injection metalorganic chemical vapor deposition on monocrystalline substrates such as LaAlO3, SrTiO3, and MgO. The pulsed-injection technique allows one to control precisely the amount of precursors delivered to the deposition chamber and thus the thickness of each individual layer. The period of the superlattices depends indeed linearly on the number of injected droplets. In our deposition conditions, the average growth rates are ∼0.130 nm/injection for La0.7Sr0.3MnO3 and 0.042 nm/injection for SrTiO3, with no significant difference as regard to the substrate used. The strain’s state of the superlattices depends on the relative thicknesses of the La0.7Sr0.3MnO3 and SrTiO3 layers and also on the substrate used. Finally, the deposition of superlattices with ultrathin interlayers of few unit cells has been demonstrated.

Deposition of SrRuO3 films and SrRuO3/YBa2Cu3O7 heterostructures by pulsed injection MOCVD

Single liquid source pulsed injection MOCVD technique was applied for the deposition of epitaxial SrRuO 3 films and SrRuO 3 /YBa 2 Cu 3 O 7 heterostructures on various monocrystalline substrates (LaAlO 3 , SrTiO 3 , NdGaO 3 , MgO, YSZ, sapphire). Sr, Y, Ba, Cu 2,2,6,6-tetramethyl-3,5-heptanedionates and Ru 2,4-pentanedionate (acetylacetonate) were used as precursor materials, 1,2-dimethoxyethane as a solvent. Deposition conditions were optimised to obtain epitaxial films and heterostructures and the influence of substrate material on films' microstructure and electrical properties was studied. The best SrRuO 3 /YBa 2 Cu 3 O 7 heterostructures which were in-situ deposited at 825 °C exhibited rather sharp superconducting transition at about 91 K and critical current density >10 6 A/cm 2 at 77 K.

Epitaxial growth of Fe on GaAs by ion beam sputtering

The epitaxial growth of ferromagnetic metals onto semiconductors is being extensively studied, and one of the reasons is the potential application for magneto-electronic devices. For this, a good quality interface between magnetic metal and semiconductor is necessary. The work presented here is concerned with Fe contacts grown epitaxially on (1 0 0) GaAs substrates. For this purpose, 25 nm thick Fe films were deposited under vacuum (∼10 −7 Torr) by ion beam sputtering onto monocrystalline substrates. The deposition method consists in sputtering an iron target with argon ions. The ejected Fe atoms, having energy of about 10 eV, are then deposited onto the substrate. The first part of the study deals with the optimisation of deposition parameters such as substrate temperature and surface cleaning before sputtering. In the second part, the deposited films are studied using X-ray diffraction and high resolution transmission electron microscopy. The Fe films deposited at room temperature are found to be polycrystalline. On the contrary, the Fe films deposited at about 300°C are found to have a monocrystalline structure and to present a perfect epitaxial relationship with the (1 0 0) GaAs substrate.

Quantitative analysis of a-Si 1− xC x : H thin films by vibrational spectroscopy and nuclear methods

Thin amorphous hydrogenated silicon–carbon films, a-Si 1− x C x : H were deposited by magnetron sputtering on glass and mono-crystalline substrates with carbon content from x=0.2 to 1, wide variation of hydrogen concentration and different degrees of structural ordering. The obtained films were investigated by Fourier transform infra-red (FTIR) spectroscopy, Raman spectroscopy, Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA). The results of the quantitative analyses obtained by the above-mentioned techniques were compared. It has been concluded that the applied vibrational methods can be used quantitatively which enables estimation of the degree of chemical ordering in the analysed samples.

Electrical and photoelectrical behaviour of CdTe structures

The electrical and photoelectrical behaviour of Au/n-CdTe junctions prepared on CdTe monocrystalline substrates and CdTe epitaxial layers grown on n + GaAs substrates were studied. The electrical and photoresponse properties depended very strongly on the parameters of the compensated high-resistive layer at the CdTe surface formed by annealing during preparation.

Epitaxial NiMnSb thin films prepared by facing targets sputtering

We have prepared high-quality epitaxial NiMnSb thin films by facing targets sputtering (FTS), using an MgO monocrystalline substrate with an Mo-buffer layer. The epitaxial growth relation has been found to be (1 0 0)NiMnSb∥(1 0 0)Mo∥(1 1 0)MgO. Optimum deposition conditions have been determined to achieve highly ordered, continuous films with low rms roughness. The magnetic and transport properties of these films are comparable to that of bulk single crystals and are found to be independent thickness in the range 100–1000 Å. The residual resistivity in particular ( ρ =5.3 μΩ cm for a 1000 Å films) is much lower than what has been reported so far in the literature. All these features should ensure a high degree of spin polarisation and a minimum spin-flip scattering in multilayered structures, thus enabling the use of these films for high-quality TMR/GMR devices fabrication.

Structural and electrical properties of silicon epitaxial layers grown by LPE on highly resistive monocrystalline substrates

The present paper reports on the properties of liquid-phase epitaxy (LPE) silicon layers grown on monocrystalline highly resistive (1 0 0)-oriented float zone (FZ) silicon substrates. All layers were grown in an indium/gallium solution saturated with Si at temperatures near 920°C. For the optimisation of layer properties for solar cell applications, parameters such as growth rate and Ga concentration of the In solution were varied. Hall measurements, X-ray spectroscopy, mechanical surface profiling (Dektak) and a lifetime analyser were used to characterise the 100–200 μm thick LPE layers.

Strain Related Effects on the Structure and Magnetic and Magneto-Optical Properties of Epitaxial MnxPt1-xThin Films

Thin epitaxial and polycrystalline MnxPt1-x films with 0 ≤ x &#8804 0.38 were prepared by molecular beam epitaxy on (001) SrTiO3 substrates. RHEED patterns confirm the epitaxial growth of the epilayers on the monocrystalline substrate. X-ray diffraction measurements reveal an anomalous structural strain-induced phase transition from the AuCu3 to the AuCu structure. The Curie temperature of strained epilayers is enhanced compared to polycrystalline films, while the magnetization is reduced. Magnetization curves for epitaxial films of (001) and (111) orientations are shown. Magneto-optical spectra of (001) oriented MnPt3 films show a remarkably large Kerr rotation of −0.82° at 1.1 eV.

Magnetic domains and magnetization reversal in epitaxial Fe layers patterned by the atomic saw method

We present a study of the magnetic domains structure and the magnetization reversal in systems of stripes and dots patterned on Fe films by the atomic saw method. Continuous epitaxial 50 and 20 Å Fe films have been grown by molecular beam epitaxy deposition method, then by applying strain on MgO monocrystalline substrate and controlling the dislocation slipping, micronic iron stripes and dots have been obtained. For the system of 1.4 μm wide stripes characterized by a strong uniaxial magnetic anisotropy (Ha=1500 Oe) resulting from a uniaxial relaxation of Fe lattice parameter, large magnetic domains have been observed by Kerr microscopy imaging. This structure is not directly correlated to the geometry of ribbons. It reveals the strong influence of the mutual dipolar coupling leading to a quasi-collective magnetization reversal. In contrast, Kerr microscopy observations done on samples structured into 1–3 μm dots show that the domain wall propagation is hindered by the net of orthogonal steps generated by the process. The domain architecture is then directly twinned to the geometry of dots. Both dot mean size and effective size dispersion which is imposed by the dipolar field seem to be the two relevant parameters that govern the two steps magnetization reversal. Calculations of coupling dipolar field are done showing its strong influence upon the magnetization reversal in the stripes case.

Thin (Hg,Pb)Ba 2CaCu 2O y films prepared from thermally evaporated precursors by post annealing in Hg-atmosphere

Superconducting (Hg,Pb)Ba 2CaCu 2O y thin films have been prepared in a two step process. Approximatively 0.2-μm-thick Ba–Ca–Cu–O or Pb–Ba–Ca–Cu–O precursor films have been deposited on MgO (100) monocrystalline substrates by a sequential evaporation method. Hg was then introduced into the precursor in a closed silica tube. The surface morphology was characterized by SEM, the composition of the superconducting phase was determined by wave dispersive X-ray electron microanalysis. Phase identification was carried out by X-ray diffraction. The c-axis-oriented plate-like crystals of the Hg-1212 and (Hg,Pb)-1212 phase were weakly connected. Although coverage of the substrate was uneven, we were able to measure transport superconductivity. The partial substitution of Hg by Pb did not significantly influence the T c values. For both the Pb-free and Pb-doped Hg-1212 samples T c(on)-values of about 132 K and the zero resistance temperatures T c(0) from 105 to 117 K were determined.

Crystalline silicon thin films: A promising approach for photovoltaics?

In this paper we review the achievements in the field of silicon crystalline thin film solar cells and correlate these with the different types of growth techniques and substrates. As a starting point we discuss the characteristics of photovoltaic devices based on the use of highly doped monocrystalline substrates as mechanical carriers for the thin films. These films are epitaxially deposited from the gas (CVD) or liquid phase (LPE). The comparison of both techniques is extended to growth on defective silicon substrates, i.e., multicrystalline wafers or silicon ribbons. The intrinsic grain boundary recombination activity in the thin films is assessed as a function of the deposition technique. Bulk passivation by hydrogenation considerably improves the recombination properties. The optimization of the hydrogen passivation conditions is looked at in conjunction with the used surface passivation process. This review is completed with the approaches to realize thin film cells on nonsilicon substrates, including recrystallization in solid and liquid phases.

Some aspects of the mechanism of the wet anisotropic etching of crystals and their consequences for a process simulation

Some essential details of the dissolution process of monocrystalline substrates are reviewed. Based on this, some considerations about possible approaches for the simulation of these processes, including a short evaluation of these approaches, follow. In order to give some insight into the problems related to the programming of geometric etch simulators, one of these approaches for 3D simulation is presented in more detail.

Influence of surface oxidation on the photoelectron diffraction intensities from InP single crystals

Abstract The Monte Carlo method was used to calculate the influence of amorphous overlayers on the angle-dependent intensity distribution due to photoelectron diffraction (XPD) in monocrystalline substrates. The influences of the overlayer thickness, the elastic and inelastic mean free paths in the amorphous overlayer, the shape of the initial intensity distribution, as well as the overlayer chemical composition, on XPD is discussed and some trends are formulated. The simulated P 2p intensities of oxidized InP agree with the experimental data. The effect of elastic scattering on the intensity minimum around the detection angle 18° is stronger than that of inelastic scattering. A new method for the thickness determination of thin overlayers on single ecrystals is discussed.