AgInSe2 crystals were grown by Bridgman technique. The crystals were identified structurally by X-ray diffraction technique. Measurements of electrical conductivity and Hall effect were performed in the temperature range (138 K - 434 K) and (220 K - 488 K) for thermoelectric power measurements. From these measurements, many physical parameters were determined. The energy gap was calculated to be 1.24 eV. The conductivity type was found to be n-type. Crystallite size (D) of the obtained AgInSe2 crystals was calculated to be 70 nm. The lattice parameters for the prepared crystals were a = 6.0938 ? and c = 11.7775 ?.
The Ag-In-Se ternary semiconductors have great potential for the photovoltaic applications especially for deposition as an absorber layer for solar cells as AIBIIIC2VI-type chalcopyrite ternary semiconductor materials [
The crystals of AgInSe2 were grown by Bridgman technique. According to this technique, the samples have been prepared by the direct melting of the starting materials (Ag, In and Se) in quartz ampoule which was sealed under vacuum of about 10−4 Torr. The silica ampoule and its charge were mounted in the first zone of a threezone tube furnace. The temperature in the first zone was higher than the melting point, and then the temperature was kept about 24 h for complete melting and mixing of the starting materials. The temperature of the middle zone of the furnace was 1073 K corresponding to the crystallization temperature of AgInSe2 as reported in the phase diagram [
Samples of rectangular form of 7.4 × 2.8 × 0.8 mm3 dimensions were used for performing the electrical conductivity and Hall coefficient measurements. In this way, the length of the sample was adjusted to be nearly 3 times its width to avoid Hall voltage drop [
For thermoelectric power measurements, the investigated sample was adjusted to be 5 mm in diameter and 10 mm in length by polishing processes. The thermoelectric power was measured by using a pressure contact sample holder with a heater and a heat sink to obtain a temperature difference between the opposed surfaces of the sample (≈3˚C). Also, an evacuated calorimeter (10−3 Torr) was used to protect the sample from oxidation and water vapour condensation at high and low temperatures, respectively. Simultaneous measurements of temperature and thermovoltage were carried out to increase the accuracy of the measurements.
where l is 1.540598 Å for CuKα and q is the Bragg angle.
perature range (138 - 273 K), representing the extrinsic region, s increases slowly with temperature as a result of the transition of the carriers from the impurity level to the conduction band. The activation energy DEd was found to be 0.06 eV as computed in this range. In the same curve, one can notice that the transition region lies between 273 and 330 K. Above 330 K, the intrinsic conduction region begins where s increases. This reveals that both electrons and holes contribute to the conduction at this high temperature range. The temperature dependence in the intrinsic conduction follows the relation:
where σo is the pre-exponential factor and DEg is the energy gap. From
The calculated energy gap from this relation equals 1.24 eV which is in agreement with that previously obtained from the conductivity work. Finally, the charge carriers concentration at room temperature amounts 1.5 × 1016 cm−3 for the AgInSe2 crystals.
The thermoelectric power (TEP) measurements of AgInSe2 were carried out as a complementary part to the electrical conductivity and Hall effect. The relation between thermoelectric power α and the temperature is depicted in
where b is the ratio of electron and hole mobility
Another important equation was employed in the extrinsic region [
According to this equation the relation between α and lnT was drawn. Then from the intercept of the line (in the impurity region) with the α-axis, we got
where A is a constant depending on the scattering mechanisms.
The similar behavior in
AgInSe2 crystals were grown by Bridgman technique. The results of investigations were carried out to determine the structural, electrical and thermoelectric power properties of the obtained AgInSe2 crystals. From these measurements, many physical parameters were estimated. Crystallite size (D) of the AgInSe2 crystals was calculated to be 70 nm. The estimated values of lattice parameters of AgInSe2 are a = 6.0938 Å and c = 11.7775Å. The energy gap was found to be 1.24 eV. Conductivity type was found to be n-type.
The authors acknowledge the Deanship of Scientific Research, Najran University, Najran, Saudi Arabia, for providing financial support (project no. NU 32/11).