Theoretical analysis and experimental results on the modulated photocarrier grating technique

SCHMIDT, J. A.; BUDINI, N.; VENTOSINOS, F.; LONGEAUD, C.

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH

Wiley-VCH Verlag

Lugar: Weinheim; Año: 2010 vol. 207 p. 556 - 560

0031-8965

We present a complete theoretical analysis of the modulated photocarrier grating method (MPG). Our calculations show that the response of the sample will be not only a photocurrent modulated with the frequency f of the illumination, but also a response in dc and with frequency 2f. In order to put to test our calculations, we implement experimentally the MPG technique and we apply it to a hydrogenated amorphous silicon sample. We verify the existence of a response at frequency 2f, and we measure the relative intensity of this signal – which compares well with the result of our theoretical calculation. We also show that under certain conditions the density of states (DOS) at the quasi-Fermi level for the majority carriers is related to the ratio of the MPG and modulated photoconductivity (MPC) signals. We present a simple formula that allows estimating the DOS as a function of energy by changing the temperature and the generation rate.