The results of experimental investigations of the electrical conductivity, magnetoresistance and Hall effect in the semiconductor TlSe with a chain structure are presented. The measurements of electrical conductivity have been carried out in two directions, i.e. parallel and perpendicular to the crystal c axis (the chain orientation). Galvanomagnetic measurements were made in magnetic fields of up to 60 kOe at different orientations of the magnetic and electric fields. The impurity conductivity is metallic in character with a negative magnetoresistance at low temperatures. The authors show that the low-temperature data can be explained by the model considering TlSe as a disordered system with a low-dimensional conductivity near the percolation limit.
The time resolved photoluminescence ( PL ) spectra of nanocrystalline Si layers formed with the help of YAG laser ( 2L 1.06 tm, Ep=O.3 J, tp2*1O 5 ) modification of the monocrystalline Si were investigated. PL was excited by pulse nitrogen laser ( A =337 nm, tp=7* iO 5, Ep2*105 J ). It W.5 established a prominent manifestation of the blue band (X=420nm). There are two sets of time decays observed in PL relaxation spectra. The fast decays are observed in the wide band from 420 to 700 nm while the slow time decays are observed in wave range from 500 to 850 nm. An analysis of the amplitude and time characteristics of PL spectra allow to conclude that the fast time decays are determined by volume energy levels in nanocrystalline wires with a variable cross-section and with the short lengths conditioned by the laser induced high defects concentration. The slow part of PL kinetics is approximated by stretched exponent, characteristic of disordered systems, has exponential spectra dependence. This attests the predominance of the tunneling mechanism controlling the velocity of recombination. The obtained results count in favour of quantum confinement model of the porous silicon ( PS ) origin. From practical terms the laser assisted method proposed may be useful for the pattern designed PS layers formation despite of the methods using the photoresist or ion implantation.
. INTRODUCTIONThe interest to the porous silicon ( PS ) layers is connected with the its ability to emit visible light and with the just first advantageous attempts of creation of the electroluminescence light emission sources. It is customary to produce the PS layers by electrochemical and stain etching. As this takes place the laser radiation was used for stimulation of the chemical etching . It were observed 2,3,4 the light induced degradation and PL enhancement by laser action. In our previous work we have proposed to use the laser irradiation of the monocrystalline Si before stain etching in order to form the PS layers with pattern designed. The basis for considerably increasing of contrast of pattern PL intensity was the idea of the etching velocity enhancement in highly disordered monocrystalline Si wafer areas due to increasing of the defects concentration by laser radiation.We have observed the two wide bands "blue" ( 2max 420 nm ) with the fast PL decay and "red" ( mx 650 nm) with the fast and slow decay times. A large body of research of the PL PS don't yet allow to consider that PL PS originis conclusively established. Nevertheless many of results suggest the quantum confinement model 6• In this work we have continued the investigations of the PL spectra relaxation peculiarity of PS layers produced with the help of laser radiation ( PSLR ). As a consequence it is supposed that the fast component is determined by geminate recombination in the framework of quantum confinement model in nanocrystalline wires with variable crosssection. An analysis of the slow decay time indicates that e-h recombination mechanism is controlled by escape of electron...
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