Introduction

Many lifetime measuring methods as QSSPC, µPCD or CDI, as well as MDP suffer from an anomalous high measured lifetime at very low injections. This effect is due to trapping centers in the sample. These trapping centers are very important, in order to understand the behavior of carriers in the material and can also have an effect on solar cells.

Aim

The aim is to measure the concentration and the activation energy of these trapping centers as accurately as possible.

Solution

With an injection dependent measurement of the photoconductivity at steady state and the lifetime it is possible to determine the trap density and the activation energy. With MDPmap09 these measurements can be very accurately and easily done, since the photoconductivity and the lifetime can be measured with just one measurement. The injection can be varied with a varying laser intensity.

From the lifetime curve the lifetime at low injection Τ_LLI can be determined and the photoconductivity is fitted with the slightly modified model of HORNBECK and HAYNES [7]. The trapping density N_T and the activation energy E_A are the fitting parameters.

Results

MDPmap09 allows to measure injection dependent photoconductivity and lifetime curves, so that the trap density and activation energy of trapping centers can be determined. With this it is possible to investigate the origin of traps and there influence on for example the efficiency of solar cells.

For more information read:
[1] J. A. Hornbeck and J. R. Haynes, Physical Review 97, 311-321 (1955)
[2] D. Macdonald and A. Cuevas, Applied Physics Letters 74, 1710 - 1712 (1999)