A. Escobosa

Phase diagram of AlN:(Ga, As)

Self-assembling of 1As4Ga tetrahedral clusters in zinc blende AlN doped with Ga and As in the ultradilute As impurity limit is described by a phase diagram. The occurrence of these clusters is an initial stage of self-assembling. The final stage of self-assembling when all As impurities are in 1As4Ga clusters is reached at a finite temperature. Both stages are results of the second-order transitions. The conditions of these phase transitions are represented. It is shown that the phase diagram of wurtzite AlN:(Ga, As) should be quantitatively similar to the considered zinc blende one.

Undoped and fluorine-doped spray deposited SnO2 films: growth and characterization

The incorporation of fluorine in SnO2 layers deposited using the spray pyrolysis technique has been studied. Fluorine doping was achieved by adding hydrofluoric acid. An anomalous behaviour of electrical properties was observed on layers grown under 350°C. Resistivities as low as 5 × 10−4 Ω · cm, Hall mobilities as high as 24 cm2/V · s and effective carrier concentrations up to 1021 cm−3 were obtained in a reproducible manner. Measured carrier concentrations were always lower than fluorine contents in the solution. Average optical transmissions on the whole visible range as high as 90% for the best conductive films, were observed for layers approximately 500 nm in thickness. The best Haackes figures of merit were about 4 × 10−2 Ω−1. These films are highly resistant to wearing conditions and chemically stables.

Graded composition CdxZn1−xTe films grown by Isothermal Close Space Sublimation technique

Abstract Graded composition CdxZn1−xTe films were prepared by growing several alternate layers of CdTe and ZnTe by the Isothermal Close Space Sublimation technique. The thickness of both kinds of layers was modified along the structure to produce an increase of the average concentration of CdTe towards the surface of the films. Due to Zn/Cd inter-diffusion during the growth process the sequence of layers was converted into a relatively smooth graded composition film. According to X-ray diffraction characterization the layers grew coherently with the (100) oriented GaAs substrates although they showed a relatively high mosaicity. θ−2θ plots show very wide diffraction peaks as expected from variable composition samples. The band gap grading effect in light absorption was also verified through transmission measurements, using transparent substrates. Graded composition profiles of the thin films were confirmed by x-ray photoelectron and secondary ion mass spectroscopies. Moreover, quantitative Cd, Zn and Te profiles were obtained by the analysis of Rutherford backscattering spectra of the samples. This analysis showed a CdTe molar fraction profile ranging from approximately x=0.8 at the surface of the sample and x=0.35 at the interface with the substrate. The possibility of growing graded composition layers using a simple and cost-effective procedure was demonstrated. This could be interesting in technological applications like CdxZn1−xTe layers of variable composition in CdS/CdTe solar cells.

Characterization of Thin Films of Conjugated Polymer (BEHP-PPV) -co-(MEH-PPV) for OLEDs Aplication

(BEHP-PPV)-co-(MEH-PPV) is a highly soluble copolymer, more stable to photo-oxidation process than other phenyl-substituted PPV derivatives, which is appropriate to use as the active layer in organic-based light emitting devices (OLEDs). In this paper we present optical properties such as the refractive index, the extinction coefficient, and the optical gap between HOMO and LUMO levels of these polymer films, determined by absorption and photoluminescence measurements. We also show the J-V characteristics of single-layer diode structures and their relation with the injecting electrodes. It was also studied etch properties of the film looking for compatibility with photolithographic processes

Vapor Phase Growth of High-Quality Bi-Te Compounds Using Elemental Bi and Te Sources: A Comparison Between High Vacuum and Atmospheric Pressure

Bismuth telluride (Bi2Te3), traditionally used in the industry as thermoelectric material, has deserved much attention recently due to its properties as a topological insulator, a kind of material that might have relevant applications in spintronics or quantum computing, among other innovative uses. The preparation of high-quality material has become a very important technological task. Here, we compare the preparation of Bi2Te3 by physical vapor transport from the evaporation of elemental Bi and Te sources, under either low pressure or atmospheric pressure. The layers were characterized by different techniques to evaluate its structural properties. As a result, it is concluded that, as a consequence of the different transport regimes, films grown at atmospheric pressure present better crystal quality.

Controlling the Epitaxial Growth of Bi2Te3, BiTe, and Bi4Te3 Pure Phases by Physical Vapor Transport

Bi2Te3 is a well-studied material because of its thermoelectric properties and, recently, has also been studied as a topological insulator. However, it is only one of several compounds in the Bi-Te system. This work presents a study of the physical vapor transport growth of Bi-Te material focused on determining the growth conditions required to selectively obtain a desired phase of the Bi-Te system, i.e., Bi2Te3, BiTe, and Bi4Te3. Epitaxial films of these compounds were prepared on sapphire and silicon substrates. The results were verified by X-ray diffraction, Raman spectroscopy, and Rutherford backscattering spectrometry.

Physical vapor transport of Bi2Te3 using elemental Bi and Te sources

A novel procedure to obtain micro and nanocrystals of Bi2Te3 is presented. The crystals are obtained by physical vapor transport using Bi and Te as sources. They were characterized by x-ray diffraction and scanning electron microscopy. Different kinds of structures as faceted crystals, strips and tubes were found at different temperatures. X-rays diffraction indicated that crystals were oriented with the (001) planes parallel to the surface.

A comparative analysis of synthesizing gallium nitride films: On gallium arsenide and sapphire substrates

The characteristics of gallium nitride (GaN) films growth on gallium arsenide (GaAs) and sapphire (Al2O3) by Metal-organic vapor phase epitaxy (MOVPE) system are presented. Comparing the results we can saw the advantages and disadvantages of use one or other substrate in order to find the best experimental conditions for obtain c-GaN films with good properties.

A comparative analysis between nitride films on GaAs and epitaxial films of GaN by MOCVD system

In this paper we report the conclusions about the analysis between the characteristics of nitrided thin gallium nitride (GaN) films on GaAs and epitaxial GaN films on buffer nitrided films. We use the metal-organic chemical vapour deposition technique for synthesize these films. Also ones films were characterized using X-ray diffraction (XRD), photoluminescence (PL) and atomic force microscopy (AFM).

Light Enhanced MOCVD Growth of GaN

The decomposition of ammonia in the MOCVD growth of GaN has been assisted by the use of strong illumination. Epitaxial growth was successful at 700oC and ammonia flow rates as low as 50 sccm.