A series of PbTe/PbEuTe double barrier samples with different barrier widths were successfully grown on BaF2 substrates by molecular beam epitaxy. The electron concentration of PbTe spacer and well layers was controlled by the deviation from stoichiometry, while the buffer and cap layers were intentionally doped with bismuth to obtain low-resistivity layers to be used as top and bottom contacts. Assuming 50% of band offset, a barrier height of 150 meV was determined by infrared transmission measurements, corresponding to a PbEuTe barrier with 5% of europium content. The structural parameters of the samples were accurately determined by combining the measurement in a high-resolution x-ray diffractometer in the triple-axis configuration with a simulation within the framework of dynamical theory of diffraction.

A series of SnTe layers with thicknesses varying from 0.42 to 9.1 µm were grown by molecular beam epitaxy on (111) BaF2 substrates. The SnTe lattice parameter was found to be 6.331 Å as determined from x-ray diffraction spectra measured in the triple-axis configuration. The FWHM of the (222) SnTe x-ray rocking curves indicated a good crystalline quality and an unusual dependence on layer thickness. Atomic force microscopy (AFM) of the SnTe surface revealed spirals with monolayer steps formed around threading dislocations, similar to the PbTe on BaF2 epitaxy. The dislocation density was estimated from the AFM picture to be 9x10(8) cm-2. Small black pits corresponding to holes that were left during growth were also observed on the AFM images. Sn diffusion can be a possible reason for these pits and the relatively high dislocation density. Electrical measurements showed that the SnTe epilayers present a typical p-type carrier concentration around 10(20) cm- 3 almost temperature independent and a Hall mobility which decreases from 10(4) to 10³ cm²/V.s as the temperature increases from 10 to 350K.

PbTe mesa diodes were fabricated from a series of p - n junctions grown on BaF2 substrates. For this series, the hole concentration was kept constant at 10(17) cm-3 and the electron concentration varied between 10(17) and 10(19) cm-3. Capacitance versus voltage analysis revealed that for n > 10(18) cm-3, a one-sided abrupt junction is formed. The direct and reverse branches of the current versus voltage curves exhibited different forms among the diodes. The R0A product varied between 0.23 and 31.8 omegacm², and the integral detectivity ranged from 1.1x10(8) to 6.5x10(10) cmHz½W-1. The performance of the best PbTe photodiodes fabricated here is comparable to the commercial InSb and HgCdTe infrared detectors, and to the PbTe sensors grown on Si substrate.

In this work we investigate the electrical properties of PbTe p - n+ junction. Mesa diodes were fabricated from p - n+ PbTe layers grown on (111) BaF2 substrates by molecular beam epitaxy. From the analysis of the current versus voltage characteristic measured at 80K, the incremental differential resistance and the series resistance were determined. The capacitance versus voltage curves were measured at a frequency of 1MHz. The one-sided abrupt junction was checked through the 1/C²xV plot. From the linear fit, the hole concentration and the depletion layer width in the p-side were obtained. The high detectivity values measured for the p - n+ PbTe diode confirm that it is very suitable for infrared detection.

Resisistivity and Hall measurements were performed at temperatures from 10 to 320K on Bi-doped PbTe layers grown on (111) BaF2 by molecular beam epitaxy. Samples with electron concentration varying from 1x10(17) to 4x10(19)cm-3 were obtained. Results indicated that all offered Bi atoms in the vapor phase were effectively incorporated in the PbTe as active donors. No thermal activation in the whole doping range was observed, indicating that the Bi donor level lies resonant with the conduction band. The mobility curve showed that the PbTe layers tend to a metallic behavior as the electron concentration increases. A value around 1x10(19) cm-3 is suggested for n+ PbTe contact layers in device application.

Epilayers of Sn1-xEu xTe (0 < x < 0:03) were grown by molecular beam epitaxy on freshly cleaved BaF2(111) substrates and their structural, electrical and optical properties were investigated. The thicknesses of epilayers were about 1.5 mum and deposition was carried out at growth temperatures of 300 ºC. The structural properties were investigated by high resolution X-ray diffraction and a sharp film degradation could be observed with increasing europium content. Electrical measurements with temperature varying from 300 to 10K indicated that the epilayers present carrier concentration ranging between 3 x 10(20) and 6 x 10(20)cm-3 and a low resistivity from 6.3 x 10-5 to 1.2 x 10-4 omega.cm. From optical measurements it could be seen that spectra present a low energy edge corresponding to the beginning of intra band excitations and the high energy edge due to inter band excitations.

We report an investigation of the optical absorption spectrum, using non-polarized light, in Pb xEu1-xTe, x=0 and x=0.095, epitaxial thick layers grown by molecular beam epitaxy (MBE). The absorption edge is described by a broad band, due to the electronic transitions from the 4f7 of Eu2+ to the states in 4f6 5d configuration, as seen previously in bulk Eu chalcogenides. When a magnetic field is applied, a narrow absorption band (full width ~50 meV) emerges from the broad one. The energy of this absorption peak red shifts when the magnetic field increases, and reaches saturation when the Eu2+ attain ferromagnetic arrangement. This behaviour can be described by a localized excitation model with d - f exchange interaction.

We have studied doped superlattices of GaAs/AlGaAs composition. When the doping atoms are introduced into the barriers surrounding the superlattice, as well as to the inner ones, but with half of the concentration, the photoluminescence due to interband transitions from extended superlattice states is detected. This is demonstrated by a study of the sample´s photoluminescence in a magnetic field, whose intensity oscillates in concomitance with the SdH spectrum of electrons confined in the miniband. GaAsAlGaAs GaAs AlGaAs composition ones concentration detected samples sample s field miniband

The interfaces in InP=In0.53 Ga0.47As superlattices modulation doped with Si were investigated using magneto-transport, capacitance-voltage, and high resolution X-ray diffraction measurements. Results indicate that a thick interfacial layer is formed when InP is grown on top of In xGa1-xAs, and that Si atoms that fall in the interfacial layer have a high probability of not forming a shallow donor center. Using a simple theoretical model the width of the interfacial layer which was estimated to be 7±1 monolayers.

Using high quality epitaxial layers, we have obtained direct evidence of the band inversion in the Pb1-xSn xTe system .The samples, covering the whole composition range, were grown by molecular beam epitaxy on (111)BaF2 substrates. A minimumin the resistivity as a function of temperature was observed for all samples with Sn composition 0.35 <= x <= 0.70. In the same samples and at the same temperature, temperature dependent optical transmission measurements have revealed a change in signal of the energy gap temperature derivative, a direct evidence of the band inversion. However, the temperature for which the inversion occurs is not the one expected by the band inversion model. This discrepancy is supposed to be due to the Burstein-Moss shift caused by the relatively high hole concentration observed in these samples.

In the present study we use x-ray diffraction methods to characterize the surface of Si wafers irradiated with nitrogen by Plasma Immersion Ion Implantation. This is a non-line-of-sight ion implantation method, which allows three-dimensional treatment of materials including semiconductors, metals and dielectrics. The atomic concentration profiles in the implanted Si wafers were measured by Auger electron spectroscopy. The (004) Si rocking curve ( omega-scan) was measured in a high resolution x-ray diffractometer equipped with a Ge (220) four-crystal monochromator before and after implantation. A distortion of the Si (004)-rocking curve was clearly observed for the as-implanted sample. This rocking curve was successfully simulated by dynamical theory of x-ray diffraction, assuming a Gaussian strain profile through the implanted region. The analysis made by x-ray difraction and Auger electron spectroscopy revealed successful implantation of ions with ac- cumulated nitrogen dose of 1.5 x <FONT FACE=Symbol>10(17) </FONT>cm-3 .The Si wafers can be used as high sensitivity monitors in the Plasma Immersion Ion Implantation process, especially at the low dose range.