Lead Telluride Films Research Articles

Structural and dc conduction studies on PbTe thin films

Lead Telluride (PbTe) films of different thickness were prepared onto precleaned glass substrates under the pressure of 2 × 10−5 Torr by thermal evaporation. X-ray diffraction technique, scanning electron microscopy, and current–voltage characteristics were used to characterize the films. The structural analysis of the films was carried using X-ray diffractometer. The surface morphology was analyzed by using scanning electron microscope. The dc electrical conduction mechanism in vacuum-evaporated Al/PbTe/Al thin film sandwich system in the thickness range 500–5,000 A at different temperature (303–483 K) was found to be a modified Poole–Frenkel type. The results of variation of activation energy with applied voltage and thickness are discussed.

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.

Study of transport properties co – evaporated lead telluride (PbTe) thin films

AbstractThin films of lead telluride (PbTe) of thicknesses ranging from 1000 Å to 2500 Å have been prepared by co‐evaporation (three temperature) technique, onto precleaned amorphous glass substrates at various temperatures. The deposited samples were annealed and annealed samples were used for characterization. Resistivity of these samples was measured by four‐probe technique as a function of thickness and temperature. Activation energy for charge transport have been evaluated and found in the range of 0.09 to 0.106 eV. Thermoelectric power has been measured and found to be positive indicating that the samples are p‐type semiconducting material. Mobility variation with temperature has been estimated (evaluated) and correlated with scattering mechanism in the entire range of temperature studied. The X‐ray diffraction analysis confirmed that films are polycrystalline having cubic structure cell and lattice parameters are reported.

Crystal structure, carrier concentration and IR-sensitivity of PbTe thin films doped with Ga by two different methods

The comparison of the results of chemical composition, crystal structure, electronic properties and infrared photoconductivity investigations of PbTe/Si and PbTe/SiO 2/Si heterostructures doped with Ga atoms by two different techniques is presented in this work. One of these techniques is principally based on the vapour-phase doping procedure of PbTe/Si and PbTe/SiO 2/Si heterostructures, which were previously formed by the modified “hot wall” technique. The second method of PbTe(Ga)/Si and PbTe(Ga)/SiO 2/Si heterostructure preparation is based upon the fabrication of lead telluride films, which have been doped with Ga atoms in the layer condensation process directly. The lattice parameter and charge carrier density evolutions with the Ga impurity concentration show principally the different character of PbTe(Ga)/Si films prepared by these techniques. It has been proposed that complicated amphoteric (donor or acceptor) behaviour of Ga atoms may be explained by different mechanisms of substitution or implantation of impurity atoms in the crystal structure of lead telluride.

Crystallochemistry of defects in lead telluride films

Crystallochemistry of defects in lead telluride films

Mechanisms of formation and charge states of intrinsic defects in lead telluride films

A crystallochemical model of the vapor-phase epitaxy of lead telluride films is suggested. The model is based on the simultaneous formation of singly-and doubly-charged Frenkel defects in the cationic sublattice. The results of numerical calculations based on this model are in good agreement with the known experimental data.

Hot wall growth and properties of lead telluride films doped by germanium and gallium

Hot wall growth and properties of lead telluride films doped by germanium and gallium

Study of PbTe photodiodes on a buffer sublayer of porous silicon

The formation of epitaxial lead-telluride films on a silicon substrate with a porous-silicon sublayer is investigated. In these structures vertical-type infrared photodiodes were produced using ion doping. Despite a great mismatch in the lattice constants and the temperature expansion coefficients between silicon and lead telluride, the photodiode parameters are similar to those of photodiodes in the orienting substrates.

Transport properties of lead telluride films

Vacuum-deposited lead telluride films formed at room temperature were studied for resistivity, Hall constant, mobility, carrier density and thermoelectric power between 78 and 400 K. The films were polycrystalline, semiconducting and p-type. The value of the effective mean free path obtained from the conductivity vs. 1/ T graph was comparable with that for the bulk. Mobility variation with temperature suggested the predominance of ionized impurity scattering in the entire range of temperatures studied. The effective hole mass m h ∗ was evaluated from the observed thermoelectric power and correlated with transport properties.

Dependence of optical properties of thermal evaporated lead telluride films upon substrate temperature

New results on the optical properties of lead telluride films are reported. Semi-transmitting PbTe films were prepared by thermal evaporation. It is demonstrated in detail that substrate temperature during deposition significantly influences the optical properties of PbTe films. The results indicate that PbTe films have the minimum absorption and maximum indices of refraction when deposited at the substrate temperature of 170 degree(s)C and 230 degree(s)C, from wavelengths of 4 to 15 micrometers .

Optical constants of lead telluride films in the range 5?11 ?m

Optical constants of lead telluride films in the range 5?11 ?m

Superconducting transition in thin films of lead telluride doped with thallium.

Superconductivity has been found in 0.5-..mu..m-thick films of PbTe doped with Tl which were grown on BaF/sub 2/ substrates by molecular-beam epitaxy. The observation that in the T = 0 limit the ratio of the parallel to perpendicular critical magnetic fields is 1.7 suggests that the superconductivity is a bulk property. The highest value of the critical temperature was 0.6 K, which is about a factor of 2 lower than previously reported values for bulk material and polycrystalline films grown on mica substrates.

TEM analysis of lead telluride films grown by hot-wall epitaxy on KCI and BaF 2

The structural perfection of PbTe films grown by hot-wall epitaxy on KCI and BaF 2 substrates in investigated by TEM analysis during the early stages of growth. (001) oriented square-shaped islands with edges lying along (100) and connected with each other by bridges along 〈110〉 are found for films grown on KC1 substrates, preferentially decorating cleavage steps and growth spirals of the substrate. As soon as the coalescence is completed, dislocations are generated, which glide in the (001) plane until they are pinned at the holes still present in the films. Large single crystalline layers with few grain boundaries and a dislocation density of 10 7–10 8 cm -2 can thus be grown. In the case of BaF 2 〈111〉 substrates, both (111) and (001) islands cover less than 10% of the surface and are more frequently found along cleavage steps. During the further growth they are overgrown by the (111) matrix, which consists initially of triangular pyramids with edges oriented along the 〈110〉 directions in the growth plane. During the coalescence of these pyramids again dislocations are introduced at the remaining holes and at the grain boundaries between the 〈111〉 matrix and 〈001〉 islands. Thus the higher density of dislocations (10 9 cm -2) can be understood by this effective source which is present in this epitaxial films. However, apparently monocrystalline films with mirror-like surfaces are found when the overgrowth of (001) islands is completed.

4167. The structure and growth of thin films of lead telluride and lead selenide condensed in vacuum on to amorphous substrates. (GB)

4167. The structure and growth of thin films of lead telluride and lead selenide condensed in vacuum on to amorphous substrates. (GB)

The structure and growth of thin films of lead telluride and lead selenide condensed in vacuum on to amorphous substrates

Polycrystalline films of PbSe and PbTe up to 104 AA thick were condensed at 15 to 300 AA s-1 in residual air at 10-3 to 10-8 Torr pressure on to glass and polished stainless steel substrates, initially at room temperature, at normal and oblique vapour incidence. Surface structures were determined by high-energy electron diffraction at a series of film thicknesses. Distinct regions of different crystal orientation are identified dependent on film thickness, residual gas pressure and composition, deposition rate and the nature of the source material. The relationship between the angle of vapour incidence and the tilt of the orientation axis is also established. The influence of the experimental parameters on the development of the different orientation regions is discussed and the results are compared with similar results from PbS films.

Structural analysis of lead telluride films and their sensitization

Structural analysis of lead telluride films and their sensitization

The absorption band edge of lead telluride films under quantum size effect

The absorption band edge of lead telluride films under quantum size effect

The Properties of Thin Epitaxial PbTe Films Prepared Under Very Clean and Closely Monitored Conditions

With the now available evidence that the structural and electrical properties of semiconductor films are a strong function of the conditions of preparation it has become apparent that if high mobility material films with reproducibly good electrical properties are to be realised, then preparation must be in very clean and closely monitored conditions with a tight control on important parameters. As an illustrative experiment 500Å thick lead telluride films have been grown on mica under clean substrate, clean source and clean environment conditions. SIMS surface analysis techniques were used to check the contamination state of the substrate and subsequent monitoring of the film nucleation and structure showed that a close control of film crystallography was possible. After growth the films were annealed until their electrical properties stabilised. In situ electrical measurements showed the annealed films to have near intrinsic carrier concentrations and bulk like Hall and field effect mobilities (∼500 cm2V-1sec-1) and these properties were reproducible.

Field-effect measurements on epitaxial PbTe and PbSe films

Field-effect measurements in the frequency range 30 Hz-70 kHz were carried out on {111} films of lead telluride and lead selenide by applying an electric field through the mica substrate. The results indicate two possible models for surface states at the mica interface: (i) acceptor and donor levels near the middle of the energy gap of the semiconductor, each of density 2×1012 cm−2 and about 0·05 ev apart; (ii) a uniform density of 2×1013 states cm−2ev−1 within ±0·05 ev of mid-gap. The evidence is mainly in favour of the second model. The surface-state time constant was about 100 μs at 300°K and increased rapidly with decreasing temperature. Field-effect mobilities of several hundred cm2v−1s−1 were observed, which suggests that the films could be suitable for thin-film-transistor applications.

Preparation and Properties of Single-Crystal Lead Telluride Films

Single-crystal PbTe films were prepared on NaCl substrates to examine initial growth and defect structures and to determine the variation in electrical transport properties of 2–5 μ thick films prepared with different deposition parameters. Although these films were uniformly well ordered when deposited on substrates ranging in temperature from 100 to 350°C, widely varying defect distributions were commonly seen during and following film closure. The galvanomagnetic properties of the films were not strongly influenced by deposition parameters. Nearly all the films were n-type as deposited, but conversion to p-type films was accomplished routinely by doping the films with tellurium vapor at 300°–350°C. The lowest carrier concentrations obtained for both n- and p-type films were between 9×1016 and 2×1017/cm3. These films were incorporated into discrete photosensors to determine detectivity. The maximum value obtained was D*(λmax,850,1)=2×1010 cmHz/W at 77 K.