Modulated Dual-Beam Photoconductivity in Hot-Pressured a-As2Se3 |
| R. Kaplan, B. Kaplan
Physics Division, Department of Mathematics and Science Education, Education Faculty, University of Mersin, Ciftlikkoy Campus, 33343 Mersin, Turkey |
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| The effects of dual-beam illumination on the exponent ν in the power-law relationship, Iph∝Gν, between generating flux and photocurrent, as well as carrier lifetime, temperature and electric field dependent photocurrent were investigated in hot-pressured amorphous arsenic(III) selenide (a-As2Se3) with coplanar electrodes. For these measurements, we used a focused tungsten white light and HeNe/Ar laser red/blue light as a DC and modulated light, respectively. The photocurrent due to the DC light bias is perturbed by the modulated beam. The DC light creates free electrons and holes and thus changes the occupation of the semiconductor gap states through which recombination occurs. The second, mostly monochromatic, beam is used to probe recombination processes by altering the occupation of selected gap states, thereby modulating the photocurrent. The temperature variation of the exponent ν is obtained and compared for both single and dual beam illuminations in detail. At temperatures lower than about 200 K, the single beam values of ν are almost constant and close to 1.0, but the dual beam values of ν are larger than 1.0, and thus they show superlinear behavior. In temperature region between about 200 K and 250 K, both single and dual beam values of ν are almost coincident and decrease with increasing temperatures. However, above 250 K, they saturate. The photocurrent modulation spectrum, which is dependent on temperature and the intensity of DC light, is rich in information about gap states that act as recombination centers. The second beam has no significant effects on the modulation spectrum and thus the carrier lifetime. However, it is found that the carrier lifetime under illumination strongly depends on the excitation wavelength due to the different light absorption. Therefore, the two-beam method in our photocurrent measurements offers a sensitive way of probing the recombination of excess carriers trapped in tail states and defects. We also discuss the results in terms of photocurrent models proposed. |
DOI:10.12693/APhysPolA.138.377 topics: dual-beam photocurrent, a-As2Se3, intensity- and temperature-dependence, lifetime, recombination |