Hopping photoconductivity in amorphous germanium

Abstract

The photoconductivity of amorphous germanium is measured as a function of temperature, annealing temperature, and intensity of the incident light. The photocurrent depends only weakly on sample temperature and annealing state, in contrast to the behaviour of the dark current. The dependence of the photocurrent on light. intensity is linear to sublinear. The results are explained by hopping photoconduction of excess carriers around the Fermi level. Results of model calculations are in good qualitative agreement with the experiments.E s wird die Photoleitfahigkeit von amorphem Germanium in Abhangigkeit von der Temperatur, Temperungstemperatur und Intensitst des einfallenden Lichts unt'ersucht. Der Photostrom hBngt nur schwach von der Probentemperatur und dem Temperungszustand ab, im Gegensatz zum Verhalten des Dunkelstroms. Die Abhangigkeit des Photostroms von der Lichtintensitat ist linear bis sublinear. Die Ergebnisse werden mit Hopping-Leitfahigkeit von ifberschuBladungstragern in der Nahe der Fermigrenze erklart. Ergebnisse von Modellberechnungen befinden sich in guter qualitativer nbereinstimmung mit den Experimenten.

The influence of spin defects on recombination and electronic transport in amorphous silicon

“…Another line has the considerably larger g value of 2.011, combined with an appreciably larger linewidth (AH,,(O) -20 G) ; it is observed only by shifting E , into the lower half of the gap (Voget-Grote 1977, Stuke 1977 and is seen also in photospin results , Pawlik and Paul 1977, Friederich and Kaplan 1979. It is, therefore, related to a positively charged state of a vacancy-type defect.…”

“…A light-induced E.S.R. signal (Knights, Biegelsen and Solomon 1977, Pawlik and Paul 1977, Friederich and Kaplan 1979 will be observed if the number of V-and/or V+ states is enhanced by photoexcited electrons and holes. As in the model of Anderson and Spear (1977), we assume that only the charged states near the middle of the gap, carrying a spin in the case of vacancy-type defects, act as non-radiative recombination centres N,.…”

“…Furthermore, both low temperature and high light intensity allow, in the case of luminescence measurements, the recombination centres near midgap to be partially occupied (Anderson and Spear Downloaded by [New York University] at 01:24 01 August 2015 1977) and therefore less effective. The ' saturation ' of the photoconductivity a t high N , is ascribed to a transition to hopping conduction (Fischer and Vornholz 1975). At this high defect density, most of the photoexcited electrons and holes obviously thermalize rapidly to states not far from the Fermi energy where, before recombination, they contribute to the conductivity by hopping.…”