The formation of mounded surfaces in epitaxial growth is attributed to the presence of barriers against interlayer diffusion in the terrace edges, known as Ehrlich-Schwoebel (ES) barriers. We investigate a model for epitaxial growth using an ES barrier explicitly dependent on the step height. Our model has an intrinsic topological step barrier even in the absence of an explicit ES barrier. We show that mounded morphologies can be obtained even for a small barrier while a self-affine growth, consistent with the Villain-Lai-Das Sarma equation, is observed in the absence of an explicit step barrier. The mounded surfaces are described by a super-roughness dynamical scaling characterized by locally smooth (facetted) surfaces and a global roughness exponent α > 1. The thin film limit is featured by surfaces with self-assembled three-dimensional structures having an aspect ratio (height/width) that may increase or decrease with temperature depending on the strength of the step barrier.

The formation of three-dimensional structures during the epitaxial growth of films is associated to the reflection of diffusing particles in descending terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier. We generalize this concept in a solid-on-solid growth model, in which a barrier dependent on the particle coordination (number of lateral bonds) exists whenever the particle performs an interlayer diffusion. The rules do not distinguish explicitly if the particle is executing a descending or an ascending interlayer diffusion. We show that the usual model, with a step barrier in descending steps, produces spurious, columnar, and highly unstable morphologies if the growth temperature is varied in a usual range of mound formation experiments. Our model generates well-behaved mounded morphologies for the same ES barriers that produce anomalous morphologies in the standard model. Moreover, mounds are also obtained when the step barrier has an equal value for all particles independently if they are free or bonded. Kinetic roughening is observed at long times, when the surface roughness w and the characteristic length ξ scale as w ∼ t β and ξ ∼ t ζ where β ≈ 0.31 and ζ ≈ 0.22, independently of the growth temperature.

Cadmium telluride films were grown on glass substrates using the hot wall epitaxy (HWE) technique. The samples were polycrystalline with a preferential (111) orientation. Scanning electron micrographs reveal a grain size between 0.1 and 0.5 µm. The surface morphology of the samples was studied by measuring the roughness profile using a stylus profiler. The roughness as a function of growth time and scale size were investigated to determine the growth and roughness exponents, β and α, respectively. From the results we can conclude that the growth surface has a self-affine character with a roughness exponent α equal to 0.69 ± 0.03 and almost independent of growth time. The growth exponent β was equal to 0.38 ± 0.06. These values agree with that determined previously for CdTe(111) films grown on GaAs(100).

In this work we have investigated the properties of CdTe thin films grown on glass substrates by Hot Wall Epitaxy. Its most important feature is the growth at very low temperatures, which would allow the growth even on polymer substrates. Our samples were grown at temperatures between 150 and 250 o C at a growth rate between 0.2 and 2 µm/h. The CdTe films were characterized by x-ray diffraction, scanning electron microscopy and optical transmission. The x-ray teta-2teta scans revealed films with cubic structure and a very high degree of preferential orientation. In fact, for films thicker than 1 µm, no other reflections have been observed on the spectra besides the (111), (333) The production of CdTe thin films has been investigated for many years. The semiconductor properties of this material are suitable for application in solar cells and many other optoelectronic devices such as detectors for the infrared and x-rayThe most used techniques to obtain these films are organometalic chemical vapour deposition [5], closed spaced sublimation [6], physical vapour deposition [7], molecular beam epitaxy [8], electrodeposition [9] and sputtering [10]. All these techniques have advantages and disadvantages depending on the type of application intended for the film. Parameters such as range of deposition temperatures and growth rates obtained, type of substrates used and films produced (epitaxial or polycrystalline) must all be of concern.In this work we describe the production and characterization of CdTe thin films grown on glass substrates. The growth technique used was the Hot Wall Epitaxy (HWE) and the films were characterized by scanning electron micrographs, atomic force microscopy (AFM), x-ray diffraction and optical transmission in the visible and near infrared. I. EXPERIMENTALThe HWE growth system used is shown in Fig. 1. It consists of a two furnace system, for source and substrate, separated by a shutter. The deposition occurs at pressures between 10 −6 and 10 −7 Torr, obtained by a diffusion pump.High purity commercial CdTe (99.999%) was used as source material and the source temperature can be controlled from 400 to 590 o C. In this temperature range CdTe evaporates congruently with more than 98% of CdTe molecules in the vapor. The growth rates obtained were in the range between 0.01 and 10Å/s. In this work we have used growth rates between 0.5 and 5.5Å/s.The HWE is a well established technique able to produce † Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, Caixa Postal 515, 12245-970 São José dos Campos-SP, Brazil Received on , 2003In this work we have investigated the properties of CdTe thin films grown on glass substrates by Hot Wall Epitaxy. Its most important feature is the growth at very low temperatures, which would allow the growth even on polymer substrates. Our samples were grown at temperatures between 150 and 250 o C at a growth rate between 0.2 and 2 m/h. The CdTe films were characterized by xray diffraction, scanning electron microscopy and optical t...

In this work animations of the random walk movement using a freeware Algodoo were done in order to support teaching the concepts of Brownian Motion. The random walk movement were simulate considering elastic collision between the particles in suspension in a fluid, and the particles which constitute the fluid. The intensity of velocities where defined in an arbitrary range, and we have a random distribution of the velocity directions. Using two methods, the distribution histogram of displacements (DHD) and the mean-square-displacement ∆r 2 (MSD), it was possible to measure the diffusion coefficient of the system, and determine the regions where the system presents ballistic regime or diffusive transport regime. The ballistic regime was observed graphically when the MSD has a parabolic dependence with time, which differing from the typical diffusive regime where MSD has a linear dependence. The didactical strategy for combining analytical approaches as graphic analysis, and animations in softwares with easy implementation supports the teaching and learning processes, especially in Physics were we want to explain experimental results within theoretical models.