A.M. Mancini

Melt growth of single crystal ingots of GaSe by Bridgman-Stockbarger's method

Abstract Melt growth of GaSe single crystals by Bridgman-Stockbargers method in ampoules with differently shaped bottoms has been investigated. It has been shown that the crystal perfection depends on the lowering rate and on the ampoule diameter and that the crystal orientation depends on the bottom shape and on the position of the ampoule with respect to the furnace isotherms.

Growth and habit of GaSe crystals obtained from vapour by various methods

Abstract GaSe single crystals have been obtained from vapour phase by using the following growth methods: (1) iodine transport; (2) closed tube sublimation; (3) sublimation under a vapour pressure of one of the components; (4) open tube sublimation. The first and the second method give mainly rise to plate-like single crystals, the dimensions of which depend on the growth conditions. The third method, carried out in Se vapour pressure, produces needles, ribbons, rods and well developed platelets. By the fourth method, very small crystals, shaped as needles ribbons and thin platelets are obtained, by using argon as carrier gas. For each method, the optimum growth conditions are experimentally determined, and, correspondingly, various aspects of the growth process, as for instance, the composition of the vapour phase, the transport rate, the supersaturation in the growth region, the crystal habit, etc. are briefly discussed. Furthermore, the physical properties (resistivity, conductivity type, mobility) of the crystals obtained by the various methods are measured, by using the Van der Pauw method. Finally, all the results are examined and compared, to ascertain the advantages and the drawbacks of each method of growth.

ZnO/CdTe heterojunctions prepared by r.f. sputtering

Abstract ZnO/CdTe heterojunctions were prepared by r.f. sputtering of ZnO films onto p-type CdTe single crystals. The ZnO deposition was carried out using a ZnO target and an Ar-H2 mixture as the sputtering gas. The ZnO films obtained under these conditions show a very good optical transmission (about 90%) between 0.4 and 0.8 μm and a low resistivity. The electrical properties of the ZnO/CdTe heterojunctions were studied by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements carried out at different temperatures. The dark I-V characteristics show that a multistep tunnelling mechanism controls the transport of charge carriers across the junction. The presence of interface states was shown to play an important role in the electrical properties of the junction. Tentative measurements of the solar energy conversion efficiency gave a value of about 3.5% without any attempt at optimization of the cell parameters.

The Use of GaSe Semiconductor Detectors for Monitoring High Energy Muon Beams

GaSe semiconductor detectors have been successfully tested during one year for monitoring muon beams in the GeV range in the neutrino experiment at CERN. Their performances are comparable with those of commercial Si surface barrier detectors for this particular application. Crystal growth, detec tor fabrication and characterization are briefly described. Various advantages (cost, ruggedness, resistance to radiation damage, manufacturing simplicity, etc.) are discussed.

Vapour growth of GaTe single crystals

Abstract GaTe single crystals have been obtained for the first time from vapour phase by using two methods of growth: (1) closed tube sublimation and (2) iodine assisted transport. The first method yields platelike single crystals with maximum dimensions of 8x6x0.3 mm 3 . The second method yields mostly needle and ribbonlike crystals, and only rarely a few platelets and rods. The main differences between the results of the two methods of growth are briefly discussed. Furthermore, the physical properties (resistivity, conductivity type and mobility) of the crystals obtained by both methods are measured, by using the Van der Pauw method, and compared with those of the melt grown GaTe.

Electrical properties of ZnO/CdTe heterojunctions

Abstract ZnO/CdTe heterojunctions have been prepared by RF sputtering of ZnO films on CdTe single crystals. The sputtering has been performed in an Ar/10%H2 mixture, in order to deposit low resistivity transparent ZnO films. The electrical properties of the as-deposited junctions are quite poor, but they can be improved by a post-deposition heat treatment in a H2 atmosphere. Current-voltage characteristics have been measured at different temperatures. They clearly show that current transport is dominated by a multistep tunneling/recombination mechanism, for both forward and reverse bias. The main features of junctions, prepared under different experimental conditions, are presented and discussed.

Influence of iodine doping on the electrical properties of GaSe

Abstract Systematic measurements of resistivity and mobility at room temperature have been carried out on GaSe samples, doped with different iodine concentrations, in order to investigate the influence of iodine doping on the electrical properties of GaSe. To this purpose a series of GaSe single crystals have been grown by the iodine vapour transport technique in the same experimental conditions, with different iodine concentrations in the growth ampoule. By means of the Van der Pauw method, the electrical characteristics of some samples have been measured for each growth run, together with the behaviour of resistivity as a function of temperature. The results clearly indicate that GaSe, which undoped has a p-type conductivity, becomes a n-type semiconductor with the iodine introduction. The room temperature resistivity decrease and the carrier concentration increase at larger amounts of iodine. The conductivity is controlled by some donor levels lying at about 0.32, 0.5 and 0.62 eV from the conduction band, as it has been evidenced by ϱ(T) and TSC measurements.

Closed tube sublimation growth of Ga2Se2: Solid-vapour equilibria and mass transport

Abstract A detailed study of the real conditions of Ga 2 Se 2 growth by sublimation in a closed tube system is presented. Mass flow measurements have been carried out as a function of the cross-section of the silica tubes, the thermal gradient along the growth chamber, and the sublimation temperature. With the aid of the results of pressure measurements, flow rates as a function of growth parameters have been evaluated according to diffusion theory, and compared with experimental flow rates. Useful information about the thermodynamic functions ΔH and ΔS of Ga 2 Se 2 has thus been obtained.

Growth and properties of chlorine doped CdTe single crystals

Abstract An experimental apparatus based on the Travelling Heater Method (THM) has been set up to grow high resistivity CdTe single crystals. Chlorine doped CdTe ingots have been obtained at relatively low growth temperature (800°C), by using a Te solution with small amount of CdCl2. The chlorine concentration present in the crystals, has been measured by means of the coulo-bipotentiometric titration with silver ions as titrant. Measurements of the electrical characteristics (resistivity and carrier mobility) and thermally stimulated currents (TSC) have been also carried out on the obtained crystals, in order to obtain information about the influence of chlorine in the physical properties of CdTe.