Hot-wall Vapor Research Articles

Photoconductivity and Thermoelectric Power of ZnxCd1-xSe Films

Znx Cd1-x Se (0≤x≤1) films were deposited by two zone hot wall evaporation technique. X-ray diffraction analysis of the films indicated a predominant wurtzite structure for x<0.5, which changed to zinc blende structure for x>0.7. The films had a mixed structure for 0.5<x<0.7. The films were highly resistive (resistivity varying within 3 Ω· cm to 1.5×105 Ω· cm for 0≤x≤1.0) with partially depleted grains. The optical band gap (E g), determined from the reflectance measurements, indicated a direct transition with a bowing effect in E g versus x plot. The conductivity at low temperature (for x<0.6) could be explained by thermionic emission over the intercrystalline barrier, while for higher x quantum mechanical tunneling through the barrier became predominant. The variation of the barrier height (E bd) with the intensity of illumination was obtained from the photoconductivity measurements. The majority carrier capture cross-section ( 1-4×10-18 cm2) of the grain boundary traps ( 1×1011-1×1012 cm-2) was determined. The effect of the intercrystalline barrier on the thermoelectric power measurements was also considered.

Optical properties of Zn xCd 1 − xSe films

Zn x Cd 1−x Se films (0 < 1.0) were deposited by the hot wall evaporation technique onto glass substrates. The optical band gap ( E g ) in the Zn x Cd 1−x Se films showed a bowing effect, with a bowing parameter of about 1.26. Microstructural information was obtained from X-ray diffraction and transmission electron microscopy (TEM) measurements, which indicated a predominant wurtzite structure for x < 0.5 and a zinc blende structure for x > 0.7. The grain size, determined from scanning electron microscopy and TEM, was observed to decrease with increasing zinc content in the films. The films were highly resistive and polycrystalline in nature, with partially depleted grains. An optical method, developed on the basis of the model of Dow and Redfield. was used to determine the barrier height and the density of trap states at the grain boundary region, along with the carrier concentration of the polycrystalline films. The variation of the electric field within the grains also was studied. The effective mass of the carriers varied with x and indicated a bowing effect.

Absorption tail of polycrystalline semiconductor films

A comprehensive description of the broadening of the absorption tail in polycrystalline semiconductor films has been presented by considering intrinsic inhomogeneity due to random distribution of grains and grain boundary regions and the fluctuation in potential from local thermal vibrations present at the grains and grain-grain interfaces. The model has been applied to describe the absorption data of a number of polycrystalline films. The results of the analysis on CdSe and ZnTe, prepared by hot wall evaporation, and on diamond films, prepared by plasma deposition of acetylene and hydrogen, are presented here.

Surface morphology and optical properties of ZnS:In films

ZnS films were prepared by the hot wall evaporation technique onto glass substrates at various temperatures in order to determine the optimum deposition conditions for preparation of stoichiometric films. The films predominantly had the zinc blende structure, and the surface roughness was found to decrease with increasing deposition temperature. Indium doping was found to increase the carrier concentration by one order of magnitude. The built-in electric field and mechanical stress were found to play an important role in describing the absorption tail in these polycrystalline films. The values of the density of trap states and the barrier height at the grain boundaries were determined.

Characterization and elimination of surface defects in Ga x In 1−xP grown by organometallic vapor phase epitaxy

In this paper we present a detailed study of the mechanism of formation and microstructure of hillock type defects in Ga x In 1− x P layers grown by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates. It was conclusively shown using a combination of dark field microscopy and microprobe analysis that In-containing particulate contamination is responsible for the formation of these defects. Cross-sectional transmission electron microscopy (XTEM) showed that the hillocks consisted of three distinct regions, namely, a base region within the GaAs buffer layer which is believed to be the In-containing particulate, a polycrystalline core region located just above the buffer layer/epitaxial layer interface and a highly twinned region in the Ga x In 1- x P layer. Cathodoluminescence (CL) studies showed that the hillocks contain a high density of non-radiative recombination centers and act as efficient heterogeneous nucleation sites for dislocations. It was demonstrated that a hot wall vapor etch of the reaction cell using HCl leads to the elimination of the hillocks.

Polycrystalline thin film ZnSexTe1-x: preparation and properties

ZnSexTe1-x films were prepared by co-evaporating ZnSe and ZnTe powders from a two-zone hot wall evaporation jig onto glass substrates. The optical band gaps for different x were determined and this showed a bowing behaviour. The refractive indices and extinction coefficients have been determined as a function of wavelength. Variations of surface roughness with composition and microstructural details were also reported. Grain boundary scattering effects were found to be a dominant factor controlling electron transport processes in these films.

Growth and characterization of SrS/ZnS multilayered electroluminescent thin films grown by hot wall technique

The growth of thin films of ZnS and SrS by the hot-wall evaporation technique has been investigated. By supplying additional sulfur (S) vapor, the deposition rate of ZnS was increased, allowing ZnS films to be grown at substrate temperatures over 400°C. SrS thin films were grown through the chemical reaction of Sr and S vapor with the substrate temperature in the region of 350–500°C. SrS/ZnS multilayered thin films were grown by the sequential deposition of the SrS and ZnS films. The (SrS/ZnS) 51 multilayered thin film showed X-ray diffraction lines from both ZnS and SrS layers, even when the thickness of each SrS and ZnS layer is 20 nm. The electroluminescent devices with SrS: Ce/ZnS multilayered thin films showed a greenish blue EL emission.

CdSxTe1-x films: preparation and properties

CdSxTe1-x films (0<x<1) were deposited by simultaneous evaporation of CdS and CdTe powders from a vertical two-zone hot wall evaporation jig onto glass substrates. Electrical conductivity, thermoelectric and optical properties along with microstructural properties were studied in order to derive information on the electron transport processes in the films. Raman scattering was also studied for the films.

Growth of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Films under Near-Equilibrium Condition by Hot Wall Evaporation Technique

Growth of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Films under Near-Equilibrium Condition by Hot Wall Evaporation Technique

Growth and microstructure of Cd1-xZnxS films deposited by hot-wall evaporation technique

Recent developments in the field of solar photovaltaic technology with CdS as window layer indicated that Cd1-x Znx S is more suitable as the window layer because its propeerties may be tailored by simply adjusting the Zn content. It is known that the band gap of (Cd, Zn) S increases linearly with increasing Zn in the film.We report here our studies on the growth and microstructure of thin films of cadmium zinc sulphide (Cd1-xZnxS) with the values of x in the range (0&lt;x&lt;0.27). Films were deposited by coevaporation of cadmium sulphide and zinc sulphide by the hot wall evaporation. Three different substrates (NaCl, KCl and LiF) were used for deposition of films in the thickness range 70 - 90 nanometer. The substrate, source and hot wall temperatures were 510 K, 1170 K and 480 K respectively.The microstructure of the films (fig. 1 ,2,3) were observed by transmission electron microscope (Hitachi H 600) and scanning electron microscope (Hitachi S-2300).

Studies of some wide band gap II–VI semiconductor based p-n junctions

Performances of CdTeZn xCd 1−xS, ZnTeZn xCd 1−xS and ZnTeCdTeZn xCd 1−xS junctions were studied to obtain information on the optimal processconditions for the above heterojunctions. The layers of ZnTe, CdTe and Zn xCd 1−xS were obtained by hot wall evaporation technique. Doping of the layers were provided either by intrinsic defects introduced by evaporation conditions or by coevaporation of appropriate dopants. The open circuit voltages obtained for CdTeZn xCd 1−xS and ZnTeZn xCd 1−xS were 540 and 470 mV, respectively. The short circuit currents were found to be very much dependent on the doping conditions of the absorber layers. Problems of doping of CdTe and ZnTe were discussed along with the results of doping on the cell performance and suitability of using different materials as dopants. Surface photovoltage measurements were performed to obtain minority carrier diffusion lengths.

The growth of epitaxial Cd 1−xMn xTe films by hot-wall evaporation

In this paper we report the first attempt to prepare epitaxial films of Cd 1− x Mn x Te semimagnetic semiconductor alloys with various compositions by hot-wall evaporation onto NaCl(001) surfaces under a vacuum of 10 -6–10 -7 Torr. The films were deposited from vapour phases of different compositions with various fluxes of CdTe and manganese atoms used as source materials. Both the growth rate and the manganese content were investigated under various conditions. The structure of the films was examined using transmission electron microscopy and X-ray diffractometry as a function of the temperature of the NaCl substrate between 150 and 450 °C. At low temperatures, polycrystalline films were obtained. The films became highly ordered with increasing substrate temperature. It was found that the films had (001) or (011) planes lying parallel to the NaCl(001) surface and exhibited a cubic sphalerite structure. No segregation of manganese was found from electron microprobe measurements. Discontinuous growth and the morphology of the early stages of growth were studied using extraction replica electron microscopy. The growth was found to be favoured by a three-dimensional mechanism.

Optical transitions in CdTe thin films produced by hot- wall vacuum evaporation

Optical properties of p-type CdTe films produced by the hot-wall evaporation technique were critically studied to obtain information on different parameters, e.g. refractive index and absorption coefficient. Variations in the parameters with incident photon energy indicated an indirect transition at a gap width of approximately 1.3 eV while the direct transition was observed at a gap width of approximately 1.5 eV.

The growth of epitaxial single crystal PbS 1−xSe x films by hot wall evaporation

Heteroepitaxial films of semiconducting PbS 1− x Se x on rock salt and mica substrates have been prepared and studied. The films have good crystalline perfection but have low electron mobilities, probably due to deviations from stoichiometry.

PbTe photodiodes prepared by the hot-wall evaporation technique

PbTe photodiodes were prepared by the hot-wall evaporation technique. N/p junctions were obtained by producing n +-type films by re-evaporation of Pb 1 − δTe 1 + δ from the surfaces of p-type PbTe samples placed in vacuum under non-isothermal conditions. The results of an investigation of the electrical and photoelectrical properties of the photodiodes at 77 and 300 K are presented. The influence of the tunnelling mechanism on the resistance-area product of the junctions at 77 K is considered.

PbTe photodiodes prepared by the hot-wall evaporation technique

PbTe photodiodes were prepared by the hot-wall evaporation technique. N/p junctions were obtained by producing n +-type films by re-evaporation of Pb 1− δ Te 1+ δ from the surfaces of p-type PbTe samples placed in vacuum under non-isothermal conditions. The results of an investigation of the electrical and photoelectrical properties of the photodiodes at 77 and 300 K are presented. The influence of the tunnelling mechanism on the resistance-area product of the junctions at 77 K is considered.

Influence of air on the electrical properties of Pb1- xSnxTe layers on a mica substrate

We studied the influence of air on the electrical properties of Pb 1- x Sn x Te ( x ≈ 0.20) layers deposited on a mica substrate by the hot-wall evaporation technique. Long-term measurements (for 3 years) as well as in situ measurements of the Hall coefficient, mobility and resistivity of samples with hole and electron conductivity were carried out. The variations of these parameters with time were interpreted on the basis of the results of Sun et al., i.e. by the adsorption of oxygen on the free surface, the diffusion of tin from the bulk to the surface and the surface oxidation of lead, tin and tellurium. The results of measurements were explained in terms of the phenomenological two-layer Petritz model and by energy band bending at the free surface of the layer.

The preparation, structure and properties of Pb 0.82Sn 0.18 Te films obtained by modified hot-wall evaporation technique : Henryk Ziencik and Antoni Rogalski Electron Technol. 11, (1/2) 69 (1978)

The preparation, structure and properties of Pb 0.82Sn 0.18 Te films obtained by modified hot-wall evaporation technique : Henryk Ziencik and Antoni Rogalski Electron Technol. 11, (1/2) 69 (1978)

The preparation, structure and properties of Pb 0.82Sn 0.18Te films obtained by modified hot-wall evaporation technique : Henryk Ziencik and Antoni Rogalski. Electron Technol.11, (1/2) 69 (1978)

The preparation, structure and properties of Pb 0.82Sn 0.18Te films obtained by modified hot-wall evaporation technique : Henryk Ziencik and Antoni Rogalski. Electron Technol.11, (1/2) 69 (1978)