Measurement of electric field enhanced optical absorption in hydrogenated amorphous silicon



Optical properties of amorphous semiconductors are influenced by applied or built-in electric fields. Measurements of the optical absorption change of device grade intrinsic hydrogenated amorphous silicon were performed indirectly by measuring the optical transmission of the samples with and without an applied DC electric field. Effects of ambient temperature changes were limited by strict control of the ambient temperature. Temperature effects caused by self-heating of the samples were compensated in two different ways to ensure the validity of the results. The influence of temperature change on optical absorption was identified and compensated by the analysis of measurements of multiple samples with different levels of power dissipation brought about by sample conductivity variations. The second method of temperature compensation consisted of determining the temperature change of each sample during the measurements, modelling absorption coefficient change caused by the temperature change and by subtracting the calculated absorption change caused by the temperature change from the measured absorption change. Results of both methods of temperature compensation are in good agreement. The obtained results are also in agreement with the results of other researchers up to photon energies slightly above the mobility edge, where our measurements exhibit a slightly different dependency on photon energy than previously published measurements. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)