M.A. Majeed Khan

Estimation of density of localized states of a-Se100−xSbx films using electrical properties

Abstract The density of states (DOS) near the Fermi level is calculated using the dc conductivity (Mott parameters) and SCLC measurements data. The dc conductivity measurements on thin films of a-Se 100− x Sb x ( x =0,0.5,2.5, 5 and 10) are reported in the temperature range (219–375xa0K). At high temperature (314–375xa0K), the conduction occurs in the extended states while at lower temperature (219–314xa0K) the conduction due to variable range-hopping. The I–V measurements have also been done in a-Se 100− x Sb x at different electric field. Space charge limited conduction (SCLC) has also been observed in the present system.

Optical investigation of a-Se100−xBix alloys

Abstract The optical properties of a-Se 100− x Bi x thin films (where x =0.0, 0.5, 2.5, and 5) have been studied in the wavelength range 540–900 nm. It was found that the optical band gap decreases on increasing Bi concentration in the a-Se 100− x Bi x system. The value of refractive index n decreases, while the value of the extinction coefficient k increases with increasing photon energy. The dc conductivity measurement of a-Se 100− x Bi x thin films has been reported in the temperature range 349–375 K. It has been observed that the activation energy decreases with increasing Bi concentration.

Studies on vacuum evaporated PbS1−xSex thin films

Abstract The narrow gap IV–VI semiconductors have been the subject of extensive research owing to their technological importance. The fabrication of devices with alloys of these compounds with detecting and lasing capabilities has been an important recent technological development. The high quality polycrystalline thin films of PbS1−xSex with variable composition (0⩽x⩽1) have been deposited onto ultra clean glass substrates by vacuum evaporation technique. Asdeposited films were annealed in vacuum at 350 K. Structural, electrical and optical properties of PbS1−xSex thin films have been examined. The X-ray diffraction patterns were used to determine the sample quality, crystal structure and lattice parameter of the films. The dc conductivity and activation energy of the films were measured in the temperature range 300–380 K. The absorption coefficient and band gap of the films were determined by absorbance measurements in wavelength range 2500–5000 nm using FTIR spectrophotometer.

Optical band gap and optical constants in a-Se100-xSbx thin films

Abstract The optical properties of a-Se100-xSbx thin films (where x = 0, 0.5, 2.5, 5 and 10) have been studied in the wavelength range 540–900 nm. It was found that the optical band gap increases with increasing Sb concentration in the a-Se100-x Sb x system. The refractive index n decreases, while the extinction coefficient k increases with increasing photon energy. DC conductivity measurements of a-Se100-x Sb x thin films have been reported in the temperature range 349–375 K. It has been observed that the conductivity increases while the activation energy decreases with increasing Sb concentration. We correlated the optical band gap with the electronegativity of the sample. The band gap increases with the decrease in electronegativity of each sample of a-Se100-x Sb x .

Estimation of the density of localized states of a-Se100−xBix films from electrical properties

Abstract The density of states (DOS) near the Fermi level is calculated using DC conductivity (Mott parameters) and Space Charge Limited Conduction (SCLC) measurement data. DC conductivity measurements on thin films of a-Se 100− x Bi x ( x =0, 0.5, 2.5 and 5) are reported in the temperature range (219–375xa0K). At high temperature 249–375xa0K, the conduction occurs in the extended states while at lower temperature (219–249xa0K) the conduction is due to variable range hopping. I – V measurements have also been done on a-Se 100− x Bi x at different electric fields. SCLC is observed in a-Se 100− x Bi x .

Study of density of localized states of a-Se80Te20−xPbx films by space charge limited conduction measurements

Abstract The present paper reports the measurements on space charge limited conduction (SCLC) in vacuum evaporated amorphous thin films of Se 80 Te 20− x Pb x (where x =0, 2, 6 and 10). At high fields (∼10 4 V cm −1 ), the current could be fitted to the theory of space charge limited conduction in case of uniform distribution of localized states in the mobility gap of these materials. The addition of (Pb) in Se–Te results in an increase in the density of localized states.

Electrical conduction mechanism in amorphous Se80In20 xPbx films

DC conductivity measurements on thin films ofa-Se 80In20� xPbx (where x ¼ 0, 2, 6 and 10) are reported in the temperature range 200–400 K. The density ofstates near the Fermi level is calculated using the DC conductivity (Mott parameters). The conduction in the low-temperature region is found to be due to variable range hopping while that in the high-temperature region is due to thermally assisted tunneling ofthe carriers in the localized states near the band edge. 2002 Elsevier Science B.V. All rights reserved.

Low temperature hopping conduction of a-Ga5Se95−xSbx thin films

Abstract DC conductivity measurements were made on amorphous thin films of Ga5Se95−xSbx (where x=0.0, 1, 5, and 10) in the temperature range 225–375xa0K. The conduction in the low temperature region is found to be due to variable range hopping, while that in the high temperature region is due to thermally assisted tunneling of the carriers in the localized states near the band edge. The effect of the addition of Sb to Ga–Se is to reduce the density of states near the Fermi level. For any given composition, the density of states near the Fermi level decreases with increasing Sb concentration. These results were analyzed in terms of Davis and Motts model.

Electrical transport properties of amorphous Se78−x Te22Bix films

D.C. Conductivity measurements on the thin films of a-Se78−x Te22Bix system (where x = 0, 0.5, 2 and 4) are reported in the temperature range 213–390 K and the density of states (DOS) near the Fermi level is calculated using dc conductivity data. It is found that the conduction in all the samples takes place in the tails of localized states. The conduction in the high temperature region 296–390 K is due to thermally assisted tunneling of electrons in the localized states at the conduction band edge. In the low temperature region 213–296 K conduction takes place through variable range hopping in the localized states near the Fermi level.

Electrical conductivity and relaxation of Se–S–In glasses

The electrical conductivity and electrical relaxation for Se?S?In glasses have been reported in the frequency range 0.12?100?KHz and in the temperature range 303?390?K. The enhancement of dc conductivity with increasing indium content has been attributed to the increase in charge carrier mobility. The ac conductivity is found to obey the modified power law ? = ?dc + A?S + B?1. The electrical relaxation is represented in electric modulus formalism. The relaxation dynamic is independent of temperature and shows non-Debye nature.