Cadmium telluride crystals have been prepared using innovative techniques for the synthesis and purification of the feed charge. The growth of low impurity content CdTe crystals was performed by both physical vapour transport and Bridgman techniques. It was found that the resistivity of the obtained crystals was strongly connected with their stoichiometry. The characterization of the main deep levels in semiconducting and semi-insulating materials, carried out by capacitance and current techniques, is reported.

In the frame of a research project aimed at obtaining high-resistivity CdTe crystals, the authors report on the preparation of (nominally) undoped semi-insulating (SI) CdTe crystals. The method is based on the use of polycrystalline CdTe charges synthesized from 7N pure Cd and Te elements, in such a way as to ensure an atomic stoichiometric ratio (Cd/Te) equal to 1 within the weighing error. The charges are further stoichiometrically adjusted by subliming off residual excess components through effusion in semi-open ampoules vented to vacuum. By making use of these charges, undoped SI CdTe ingots, made up of large single-crystal grains, have been grown from both vapour, by closed-ampoule physical vapour transport and melt, by liquid encapsulation Bridgman technique. The yields in SI material turned out to be 100% for vapour-grown samples and about 50% for melt-grown ones. Preliminary results of this research work are presented here and briefly discussed.

In the frame of a research project aimed at preparing high-resistivity CdTe single crystals, the authors have developed as a first step, a new, low cost, fast technique which allows to synthesize from the elements polycrystalline CdTe with very low stoichiometric deviations and with a level of background impurities much lower than usually available in commercial materials. The material obtained by this technique as will be described and discussed, appears especially suitable for preparing source charges for physical vapour transport growth experiments.

A study on the uniformity of Fe-diffused semi-insulating InP wafers is presented. The electrical characterisation showed that after the diffusion annealing the wafers became semi-insulating, with resistivities generally above 108 Ω cm and mobilities in the range 3000-4000 cm2/Vs. PL and resistivity mapping showed that the short range uniformity is excellent but that sometimes the wafers exhibit long range gradients of resistivity and luminescence intensity. The gradients are believed to be associated with temperature gradients inside the annealing furnace

The control of low level impurities is still considered to play a key role in obtaining GaAs based devices with an high degree of uniformity and reproducibility. Although in the recent years the importance of appropriate post growth thermal treatments has been recognized as the most relevant step in achieving homogeneous material, the contamination reduction of the melt is a fundamental requisite for growing crystals with good electric characteristics and morphology.In this work we report on new results obtained from boron and silicon doped gallium arsenide crystals sown by LEC technique in a high pressure puller: different doping procedures for heavily Si doped crystals are described and interactions between silicon and boron in the liquid, are discussed together with the analysis of (heir distribution in the ingot.On the basis of our experimental data front crystals doped with either B or B and Si together, a tentative explanation of the incorporation mechanism of such elements is given and a comparison with previously reported results is made.

InP surfaces, with (100), (111)In and (111)P orientations were etched with HBr-K2Cr2O7-H2O (BCA) solutions. Etching could be diffusion controlled (giving rise to polishing) or purely kinetically controlled (revealing crystallographic defects), depending on the solution composition. These experimental results have been summarized in a BCA ternary diagram which allows complete surface treatment of indium phosphide. Solutions from the HBr-rich corner of the ternary diagram produce well defined crystallographic pits on dislocations. Rectangular pits formed on (100)-oriented samples are suitable for an unequivocal definition of the [011] direction. It has been shown that the high elongation factor of the pits (ratio of length to width) distinguishes the BCA system over other etchants currently used for the same purpose. From the details of the pit morphology it is possible to recognize the decoration effect and different inclinations of the dislocation lines relative to the surface.

The phosphorus pressure in equilibrium with solid InP heated at temperatures of up to 980 °C was measured using a new-concept apparatus appositely designed and manufactured. With this apparatus, all the difficulties inherent to handling of phosphorus vapor and high temperatures were overcome without making use of complicated devices such as quartz membranes or helix. This has allowed a reproducible series of measurements of the phosphorus equilibrium pressure to be made. This pressure was found to vary exponentially between 2 and 550 mbar as the InP temperature grows from 800 to 980 °C. The results are of practical interest, particularly if one considers the recent technological efforts for growing InP single crystals under P atmosphere and for obtaining semi-insulating undoped InP by thermal annealing under P counter pressure.

From the technological point of view the main task is to achieve a regular shape, good crystallographical and electrical parameters in the crystal growth process. The GaAs single crystals grown by the technology of Liquid Encapsulated Czochralski (LEC) generally have satisfactory parameters if the process is strictly controlled. In this paper we have tried to investigate the possibility of the accurate control of the diameter of the GaAs crystal in a high pressure Galaxy type puller, made by LPA, France.

Multilayer LPE of GaAs and GaAlAs using a vertical system with rotary graphite crucible has been developed. Using this equipment superlattice structures in the GaAs-GaAlAs system were grown. The layer thicknesses were varied from 20 to 500 nm. Structures up to 100 layers were deposited using constant cooling rate and step-cooling LPE methods; the growth times varied for an individual layer in the range of 1 to 50 s. It was observed that calculating the respective growth rates and layer thicknesses the experimental values differed to a great extent from the calculated data showing the insufficiency of the diffusion limited growth rate theories in our case. The doping of the multilayer structures with Si, Ge and Sn was also studied. Anomalous growth rates depending on the dopant quality were observed.

An LPE reactor with semitransparent gold shield and Al reflectors is constructed. Using these reflection mirrors a highly uniform temperature profile, as well as a fast and easy temperature regulation are achieved. The system makes possible the “in situ” observation of the saturation processes through the semitransparent shield. The system is used for the preparation of the In/GaInAsP double heterosystem using a multiwell graphite boat. Laser structures are grown with the doping of the confining InP layers. Es wird ein LPE-Reaktor mit halbtransparentem Goldschild und Al-Reflektoren konstruiert. Mit diesen Reflexionsspiegeln werden sowohl hochgleichförmige Temperaturprofile als auch eine schnelle und leichte Temperaturregelung erhalten. Das System macht eine “in situ” Beobachtung der Sättigungsprozesse durch das semitransparente Schild möglich. Das System wird zur Präparation des In/GaInAsP-Doppelheterosystems mit Hilfe eines Mehrgruben-Graphitboots benutzt. Laserstrukturen mit Dotierung der begrenzenden InP-Schichten werden hergestellt.

A new semiconductor, the pseudo-ternary GaPAsSb, has been prepared in epitaxial layer form. This quaternary can be lattice matched both to GaAs and to InP. A liquid phase epitaxial method is described to grow double hetero-epitaxial systems made from GaAs and GaPAsSb. The lattice matching has been studied using X-ray rocking curve and X-ray topography techniques. The composition and phase diagram data were also studied using different growth temperatures. In the system nearly perfect lattice matching was achieved. Luminescence measurements showed that the system can substitute for the GaAs/GaAlAs double heteroepitaxial systems conventionally used for laser diodes.

A novel vertical rotation LPE system and a new technique are described. The formation of multilayers and superlattice (SL) structures have been demonstrated with this technique. The special graphite casette and the regulation system have made preparation of these structures possible. In the GaAs-GaAlAs system multilayer structure up to the layer number of 50–100 with a periodicity of d < 50 nm were grown.

GaSb growths were performed in a vertical Bridgman arrangement to clarify the role of the radial heat loss, as the source of the radial component of thermal elastic stresses, in the formation of dislocations. Using identical ingot shapes, the variation of growth conditions — including a space experiment — has proved that correct isolation of the ampoule wall from the convection currents of the furnace can considerably decrease the dislocation density. It is concluded that the existence of radial stresses in the growing ingot has to be taken into account in both the theoretical calculations and the development of crystal growing methods.

GaAs, one of the basic materials of many electronic devices, has become widely used because of the improvements in epitaxial growth techniques. This paper presents the results obtained during the development of GaAs structures. Data are given on the optimum growth parameters, on the requirements against the raw materials, the flow velocity of gases, the growth rate of the layers, on the possibility of reducing the background impurities to 5·1014/cm3, and on the different electrical measurements performed on structures such asn ++−n b −n k ++ −n−n b −n 3 ++ ,n−n b − −n 3 and submicron layers.

Epitaxial growth of the AlGaInSb pseudo-ternary on GaAs, GaSb and InSb substrates was investigated. The LPE growth was performed using In- and Ga-rich melts and different growth parameters such as cooling rate, supercooling, etc. The heteroepitaxial systems were evaluated by several methods; the growth morphologies and layer thickness were investigated by scanning electron microscopy, the composition of the quaternary was determined by X-ray microanalysis using both energy and wavelength dispersive analysis, and the lattice matching and layer perfection were analysed using X-ray rocking curves. It was demonstrated that good quality AlGaInSb epitaxial layers and p-n junctions were formed using In-rich melts and GaSb substrates.

A high quality GaSb bicrystal was grown in a Bridgman type arrangement under microgravity conditions on board of Salyut-6. Rutherford back-scattering measurements indicate oxide and damage free surfaces. Scanning Electron Microscopy revealed microfacets on the space grown sample. The morphology of the sample suggests a crystallization quite free of a wall effect. A comparison is given between space and terrestrial GaSb ingots, showing differences in surface quality, crystal perfection and hole mobilities. In the space grown sample a μmh ≈ 2700 cm2 v-1 s-1 value was found while for the terrestrial control this value was only 2000 cm2 v-1 s-1

Structural investigations on GaSb crystals grown under microgravity and terrestrial conditions by Bridgman method, are described. Microgravity (μG) conditions resulted in a reasonable quality bi-crystal including its surface layer, as shown by both ion and electron channeling investigations.

GaSb was synthetized from Ga of 6N and Sb of 5N5 purity. After the synthesis the crystallization took place in Bridgman-type growth systems. Terrestrial and space experiments aboard Salyut-6 have been performed. In terrestrial experiments depending on the growth parameters (pulling rate, ampoule diameter, etc.) macro−, or polycrystalline ingots showing a characteristic texture have been formed. It has been observed that in wider ampoules boules of better quality have grown, the diameter of individual crystals ranging from 1–3 cm. In the space experiment a high-quality bicrystal has been formed. Examining the texture of terrestrial samples, the orientation of crystallites, the number of low and wide angle grain boundaries have been determined using electron channelling (EC) patterns.