I.N. Bandeira

Electrical properties of Pb1-xSnxTe layers with 0⩽x⩽1 grown by molecular beam epitaxy

In this work, the electrical properties of Pb1−xSnxTe epitaxial layers with Sn composition covering the whole range were investigated. The samples were grown on (111)BaF2 substrates in a molecular beam epitaxy system using PbTe, SnTe, and Te solid sources. As the alloy composition varies from PbTe to SnTe, the hole concentration increases exponentially from 1017 to 1020 cm−3 for Te-rich sources and from 1017 to 1019 cm−3 for stoichiometric ones. The resistivity of the samples, which depends mainly on their hole concentrations, shows an exponential dependence on the temperature with a slope which decreases as x goes from 0 to 1. For all Pb1−xSnxTe samples with x in the range of 0.35–0.7, the resistivity curve shows a very well defined minimum at low temperatures. This anomalous behavior is supposed to be related to the band crossing, where the energy gap temperature coefficient changes sign. The temperatures where the minimum in the resistivity occurs only agree with the ones predicted by the band inversio...

Growth of narrow gap epilayers and p-n junctions on silicon for infrared detectors arrays

Abstract Lead telluride epilayers and p-n junctions were grown on silicon substrates by hot wall epitaxy in order to construct monolithic infrared (IR) detectors arrays, using II-a fluorides as buffer layers. Schottky barriers were also made in the same epilayers to compare the figures of merit. The p-n junctions had performances comparable with the metal barriers and both devices had noise sources in addition to the expected thermal and background ones.

Reciprocal space maps of PbTe/SnTe superlattices

PbTe/SnTe superlattices were grown on (111) BaF2 substrates by molecular beam epitaxy using PbTe as buffer layers. The individual layer thickness and number of repetitions were chosen in order to change the strain profile in the superlattices from completely pseudomorphic to partially relaxed. The superlattices structural properties were investigated by making reciprocal space maps around the asymmetric (224) Bragg diffraction points and ω/2Θ scans for the (222) diffraction with a high resolution diffractometer in the triple axis configuration. With the strain information obtained from the maps, the (222) ω/2Θ scan was simulated by dynamical diffraction theory. The simulated spectra of the pseudomorphic superlattices, in which the in-plane lattice constant is assumed to be the same as the PbTe buffer throughout the superlattice, fitted in a remarkably good agreement with the measured data, indicating that almost structurally perfect samples were obtained. For the thicker superlattices, the (224) reciproca...

IV–VI Compound heterostructures grown by molecular beam epitaxy

Abstract Structural and optical characterization of some IV–VI superlattices (SL) and multi-quantum wells (MQW) grown by molecular beam epitaxy (MBE) on BaF 2 (111) substrates are shown. Three different types of systems were investigated, namely, PbTe/PbSnTe, PbTe/SnTe and PbTe/PbEuTe. High-resolution X-ray diffraction analysis was performed to determine the strain in the structures. The analysis revealed sharp interfaces and good thickness control. The transition energies between the confined levels in the wells were obtained from the absorption steps observed in infrared transmission measurements. Preliminary results on PbTe/Si heterojunction grown by MBE are also presented.

Characterization of Pb0.8Sn0.2Te films grown on KCI substrates by hot-wall epitaxy

Abstract Single crystalline Pb 0.8 Sn 0.2 Te films were grown on cleaved KC1 substrates by the hot-wall epitaxy technique. Hall concentration and carrier mobility were measured as function of compensation temperature, and the influence of the substrate temperature on layer morphology is studied.

Experimental observation of band inversion in the PbSnTe system

The band inversion in the PbSnTe compound has been observed by optical and electrical measurements. The samples, high quality Pb1−xSnxTe epitaxial layers, have been grown by molecular-beam epitaxy on (111)BaF2 substrates. Optical transmission measurements have revealed a change in signal of the energy gap temperature derivative for samples with 0.35<x<0.70. In the same samples and at the same temperature, a minimum in the resistivity has been observed, showing a interrelation between the optical and electrical measurements. However, the temperature, for which the inversion occurs, is not that predicted by the band inversion model. This discrepancy is supposed to be due to the relatively high hole concentration of these samples.

A model for the solute transport in PbSnTe growth by vapor-melt-solid technique

Abstract We investigate the basic mechanism occuring in diffusion-controlled growth of Pb 1−x Sn x Te single crystals by the vapor-melt-solid (VMS) technique. A physical model for the mass transfer by the vapor and liquid phases without parasitical convection is stated and solved with an implicit moving-boundary finite-difference scheme. It is shown that VMS allows for the attainment of good crystal axial homogeneity, through the reduction of the effective diffusion length in the vapor phase, allied to the supression of convective effects at the liquid-solid boundary. Results from numerical simulations suggest how VMS can be improved by an appropriate design of the furnace temperature profiles and translation rate. Also, the influence of non-equimolar evaporation-condensation processes at the liquid-vapor interfaces is considered; it indicates that VMS is not suited for substances whose components show large differences in volatility from the liquid phase.

Influence of interdiffusion on N-PbTe⧸P-Pb0.80Sn0.20Te heterojunction diodes

Abstract A study of the spectral response, detectivity and I vs V characteristics was made on N -PbTe/ P -Pb 0.80 Sn 0.20 Te heterojunctions HJ grown on BaF 2 substrates by the HWE technique. The results confirm that a potential barrier that appears at the HJ interface depends on the gradation width and on the relation between the N and P concentration. The PbSnTe HJ behavior indicates that the gradation model proposed for the HgCdTe HJ gives a better fit to our data than the junction migration model.