PbTe Films Research Articles

Effect of interface traps on Debye thickness semiconductor films

The presence of the boundary interface trapping states and their role in determining the properties of Debye thickness thin semiconductor films, are demonstrated experimentally, using PbTe films deposited on mica. These charged states could not be observed earlier and be studied directly, because of the screening by the relatively high carrier density of the ordinary PbTe. Thin, Debye length thickness, PbTe films with a high concentration of interface trapping centers, possess an extraordinary high resistance. In this case the thermostimulated capacitor discharge method can be successfully applied to determine the energy of these levels, their carrier capture cross-sections and their donor- or acceptor-like character. The experimental results and theoretical calculations are discussed.

Single-layer-coated beam splitters for the division-of-amplitude photopolarimeter

A design procedure is presented for a near-optimal, single-layer-coated prism beam splitter that serves as the key optical element of the division-of-amplitude photopolarimeter (DOAP). For given film and substrate refractive indices, the angle of incidence and film thickness are selected such that the ellipsometric differential phase shifts in reflection and transmission deltar, and deltat, differ by +/- pi/2, and the normalized determinant of the instrument matrix is maximized. The best results are obtained by using high-index films on low-index substrates. This is illustrated by examples of ZnS and GaP films on silica prisms in the visible and Si, Ge, and PbTe films on Irtran 1 substrates in the infrared. A 16 degrees Si-prism DOAP beam splitter at the 1.55-microm lightwave-communications wavelength is also presented. It uses a 163-nm SiO2 coating on the entrance face to satisfy the optimum delta condition at 73 degrees incidence, and the determinant of the instrument matrix is 78.23% of its theoretical maximum. The exit face of the Si prism is antireflection coated with a 208-nm Si3N4 film.

Effect of oxidation on thickness dependencies of thermoelectric properties in PbTe/mica thin films

The dependencies of the Hall coefficient R H and Seebeck coefficient S at room temperature on the thickness ( d=10–550 nm) of thin PbTe films prepared by the thermal evaporation in vacuum of n-type PbTe crystals with various charge carrier concentrations (10 17–10 19 cm −3) and their deposition on mica substrates were obtained. It was established that, with decreasing thickness of PbTe films, a transition from an electron to a hole conductivity occurs, and the inversion point shifts to smaller d values as the electron concentration in the target material increases. The experimental R H( d) and S( d) dependencies are interpreted in terms of the acceptor states created by oxygen on the film surface. These dependencies were also calculated theoretically, taking into account the existence of two types of charge carriers (electrons and holes). The theoretical curves are found to be in good agreement with the experimental data.

A twinned PbTe film induced by the 7×7 reconstruction of Si(1 1 1)

The PbTe films were grown on Si(1 1 1) substrate by hot wall epitaxy (HWE). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the films. The results show that the PbTe films are twinned ones with preferred 〈1 0 0〉 orientation. The angles of normal direction of PbTe(1 0 0) facets which are perpendicular to the surface of Si substrate are 30° or 60°. The interface energy is calculated by CASTEP module of materials studio and the reason for this phenomenon is discussed.

Structural Perfection of PbTe Films Doped with Indium during Growth on Si Substrates

Pb1 - yIn y Te films doped during growth are produced by a modified hot-wall method. According to x-ray diffraction and electron microscopy data, the films withytot 0.014 consist of two (PbTe + InTe) or three (PbTe + InTe + In2Te3) phases. The 583-K indium solubility in PbTe is determined in the ternary system Pb-In-Te. The results indicate that two pseudobinary joins, PbTe-InTe and PbTe-In2Te3 , must be examined in assessing the In solubility in PbTe.

PbTe films grown by hot wall epitaxy on sapphire substrates

A ‘hot wall epitaxy’ is applied to grow PbTe thin films on sapphire substrates with BaF 2 buffer layer deposited by molecular beam epitaxy (MBE). The microstructural and strain state characteristics of PbTe layer were examined with high resolution X-ray diffraction techniques. The epilayer is composed of two (111)PbTe‖(0001)Al 2O 3 epitaxially oriented domain variants. The domains are azimuthally rotated and their interfacial directions relative to the substrate are [011̄]PbTe‖ 2 1 ̄ 1 ̄ 0 Al 2O 3 and [1̄54̄]PbTe‖ 2 1 ̄ 1 ̄ 0 Al 2O 3, respectively. Another possible alignment of the domain variant corresponds to 3 1 ̄ 2 ̄ PbTe‖ 3 1 ̄ 2 ̄ 0 Al 2O 3 orientation. The strain state analysis of PbTe layer points to its relaxation via domain formation and high dislocation density generation in the lattice. Despite the domains formation the measured mobility of electron carriers is approximately 1600 cm 2/V s and 30 000 cm 2/V s at 300 K and 77 K, respectively. The theoretical analysis of the measured electrical properties indicates that the scattering by acoustic and optical phonons is the factor affecting the conduction process.

Growth and characterization of PbTe films by magnetron sputtering

Thin films of PbTe were sputter deposited on Si (1 1 1) wafers and glass substrates. A constant power for different times and various power levels for a constant time were applied on PbTe target. Heated and unheated substrates were used. The substrate heating to a temperature of ∼673 K was performed in situ during sputtering. Structural analysis by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM) were performed. The composition of the PbTe film was evaluated by Auger depth profile. At an appropriate combination of power and deposition time only (2 0 0) and its higher order peaks were observed in the PbTe film. PbTe films with different thicknesses in the range of 80–300 nm were deposited on the wafers. XRD data indicate that the (2 0 0) texture is influenced by the film thickness.

Comparative study of point defects induced in PbTe thin films doped with Ga by different techniques

The comparison of the experimental results, which have been received in studies of chemical composition, crystal structure, and electronic properties of Ga-doped films on Si (1 0 0) and SiO 2/Si (1 0 0) substrates, is presented in the present work. The Ga-doped PbTe films have been fabricated by two different ways. In contradistinction to the films, which have been doped by two zones annealing, the films synthesized by one-stage method using PbTe〈Ga〉 layers demonstrate the non-monotone dependence of lattice parameter and charge carrier densities with the Ga impurity concentration. Complicated amphoteric (donor or acceptor) behaviour of Ga atoms may be explained by different mechanisms of substitution Ga Pb × or implantation Ga i … of impurity atoms in the crystal structure of lead telluride.

Nonstoichiometry and solubility of impurity in In-doped PbTe films on Si substrates

The chemical quantitative composition, phase constitution, and crystal structure of doped with In lead telluride films on Si (1 0 0) or SiO 2/Si (1 0 0) substrates have been studied in this work. By EPMA and atomic absorption measurements, it has been found that the concentration of In atoms y In varied from 0.0011 to 0.045 in these deposited Pb 1− y In y Te films. The results of EPMA, SEM, and X-ray diffraction (XRD) measurements show that formation of In solid solutions in lead telluride matrix revealed not only in PbTe–InTe cross-section, but in PbTe–In 2Te 3 pseudobinary system also. The results of XRD show that the lattice parameter a PbTe of PbTe〈In〉/Si and PbTe〈In〉/SiO 2/Si heterostructures is described by nonmonotone function and does not obey the Vegard's law within concentration interval 0.0011⩽ y In⩽0.045.

The growth of PbTe on H-terminated Si( [formula omitted]) substrate by hot wall epitaxy

The PbTe films were grown on hydrogen-terminated Si(1 1 1) [H-Si(1 1 1)] substrate by the hot wall epitaxy method. These films were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and I– U measurement. The XRD spectrum revealed that PbTe films grown on H-Si(1 1 1) substrate have a preferred 〈1 0 0〉 orientation. XRD and SEM analyses showed that their crystalline quality is better than that grown on Si(1 1 1) substrates. Nucleation SEM picture shows that the growth of PbTe on Si(1 1 1) is of the Volver–Weber mode. I– U measurement indicated that n-PbTe/H–P–Si(1 1 1) heterojunction has a good junction character.

Degradation of the Thermoelectric Properties of n ‐PbTe Films in Atmospheric Oxygen

It has been shown that the behavior of the thermoelectric properties of n‐PbTe films produced at different condensation temperatures Tc depends on the time of storage in air, which is related to the physical processes responsible for the diffusion of oxygen along the crystallite boundary and on its state prescribed by condensation conditions.

Effect of non-stoichiometry on oxidation processes in n-type PbTe thin films

The dependences of the galvanomagnetic and thermoelectric properties on the thicknesses d (5–200 nm) of PbTe thin films prepared by the thermal evaporation of non-stoichiometric PbTe with 2 at.% excess lead were studied, with measurements conducted in air at room temperature on freshly grown films. It was established that with decreasing film thicknesses, an inversion of the dominant charge carrier sign from n to p takes place at d∼40 nm. A comparison of the results obtained in this work with those for PbTe films prepared from stoichiometric PbTe showed that the increase in n-type charge carrier concentration results in a shift of the inversion point to smaller d values. The observed effect is attributed to oxidation processes taking place in PbTe thin films at room temperature in air, and the effect is interpreted in terms of compensating acceptor states created by oxygen on the film surface.

Growth of In-Doped PbTe Films on Si Substrates

Data on the evaporation behavior of Pb1 – xInx (0.10 ≤ x ≤ 0.70) melts were used to devise a procedure for the growth of vapor-phase In doped PbTe thin films on Si substrates. This approach offers the possibility of growing single-phase, homogeneous Pb1 – yInyTe films of controlled composition by adjusting the composition and temperature of Pb1 – xInx (0.10 ≤ x ≤ 0.50) melts. X-ray diffraction characterization demonstrates that the films grown on Si with no oxide layer consist of slightly misoriented crystallites, with their (100) axes normal to the film surface, whereas the films grown on substrates covered with a SiO2 layer are polycrystalline, with a strong (100) texture.

Structural and optical characterization of laser-deposited PbTe films on silicon substrates

The structural and optical properties of PbTe films, fabricated using pulsed laser evaporation, are studied. The grazing incident asymmetric X-ray diffraction patterns, obtained at different grazing angles, unambiguously demonstrate that the films represent three-layered structures. Each of the layers is of one of the competitive PbTe phases—the metastable CsCl-type, the metastable GeS-type and the stable NaCl-type crystal modifications. The CsCl-type phase lattice parameter and layer thickness in the films grown on Si substrates are compared with those in the films grown on substrates with the NaCl-type structure. The energy dependence of the refractive index was obtained from the extrema of the interference fringes in the transmittance and reflectance spectra. The dependence can be interpreted by treating the films as three-layered structures with a different crystal modification of each of the layers.

Temperature dependence of the Seebeck coefficient and the potential barrier scattering of n-type PbTe films prepared on heated glass substrates by rf sputtering

Thermoelectric properties of polycrystalline degenerate n-type PbTe films have been investigated in order to understand potential barrier scattering. The Seebeck coefficients of the PbTe films obtained in this study were larger than those of bulk samples having the same carrier concentrations in the temperature range from 100 to 450 K. Some of their power factors were larger than those of bulk samples having the same carrier concentrations in the temperature range from 200 to 450 K, while their electrical conductivities were smaller than those of bulk samples. From a comparison of these results with those previously reported, we concluded that potential barrier scattering occurred at grain boundaries in our films, resulting in the above favorable changes in thermoelectric properties. By analyzing their properties using the energy filtering model, we estimated the height of grain-boundary potential barriers, which probably influenced the increases in the Seebeck coefficient. We also examined the origin of the potential barriers accordingly. Consequently, we consider that the origin of the potential barriers was mainly due to point defects, probably Te vacancies, and that the barrier height may be controlled, for example, by the preparation conditions.

Forming PbTe on Si-substrates for IR sensors

The lead chalcogenide (PbTe) layer has been grown by hot wall epitaxy directly ort 100 mm Si substrate using a barium fluoride (BaF 2 ) buffer layer. BaF 2 buffer layer was used to overcome the large lattice and thermal expansion mismatch. Structure characteristics of the PbTe films grown on silicon substrates with the BaF 2 buffer layer were investigated by x - ray phase analysis. We have fabricated PbTe on Si sensor with cutoff wavelength 5,2 μm.

Epitaxial electrodeposition of lead telluride films on indium phosphide single crystals

Epitaxial PbTe films were electrodeposited on (1 1 1) InP single crystals, from solutions containing Pb 2+ and Cd 2+ ions, the latter being largely in excess. High energy electron diffraction and X-ray diffraction reveal the formation of epitaxial films accompanied by the presence of polycrystalline PbTe. The poor epitaxy is related to a large lattice mismatch with the InP substrate. A low density of planar defects, compared with II–VI chalcogenides, is observed.

Characterization of Sputter Deposited PbTe on Si (111) for Optoelectronic Applications

ABSTRACTIV-VI compound semiconductors are of interest due to their potential application as thermoelectric material, infrared detectors and semiconductor lasers. The use of PbTe based semiconductors is usually in the middle and far infrared region. Magnetron sputtering of PbTe thin films from a single target on Si (111) was performed under various conditions. Characterization of the films shows that PbTe films on Si (111) substrate are suitable for preparation of infrared (IR) detectors. By heat treatment novel IR detectors can be developed in the electron absorption region of 4 – 10 μm.

Pb and In Codeposition in the Vacuum Growth of PbTe Films on Si Substrates

Pb1 – x In x melts were proposed to be used as In vapor sources, in combination with separate Pb and Te sources, in depositing PbTe films onto Si substrates by a modified hot-wall method. Under the assumption that the presence of Pb in Pb1 – x In x melts may raise the In partial pressure, the vaporization behavior of Pb1 – x In x (0.05 ≤ x ≤ 0.70) was studied between 900 and 1200 K in the reaction chamber of the deposition unit. Using electron probe x-ray microanalysis and x-ray diffraction, all the deposited films were shown to contain In. The In content of the Pb1 – y In y deposits varied in the range 0.002 <y < 0.07 and increased with increasing In concentration in the Pb1 – x In x melt and with increasing vapor source temperature. The vapor over molten Pb1 – x In x was shown to exhibit a positive deviation from ideality.

Transport Properties of Ga-Doped PbTe Thin Films on Si Substrates

Thin PbTe films on Si substrates were doped with Ga via annealing in the vapor produced by heating a Ga(l) + GaTe(s) mixture (GaTe(s) + L1+ Vequilibrium). Electrical measurements showed that the vapor-phase doping reduced the hole concentration in the films by more than two orders of magnitude. IR irradiation was found to reduce the resistivity of the PbTe films by a factor of 40–100. The films annealed in the vapor over GaTe(s) + L1for the longest time exhibited an anomalous temperature variation of resistance, which was interpreted as due to the limited Ga solubility in PbTe.