Optical Dlts Measurements of Localized States in Amorphous Chalcogenide Semiconductors

New combined optical/thermal method (optical DLTS) for the investigation of gap states is presented. The concentration and energy distribution of the gap states have been studied. The optical DLTS signal S(T) vs. temperature is calculated from the photoconductivity decay I(t,T). The effective levels and density of states for amorphous Se and As2Se3 films were obtained. Introduction.Recently, there has been a considerable interest in determining the concentration and energy distribution of states in the gap of amorphous chalcogenide semiconductors. The techniques for obtaining such information have been the field effect method (l), C-V method (2) , photo-capacitance method (3) , and DLTS (4-6) . However, it is difficult to obtain the gap states of chalcogenide semiconductors (Se, AseSea), because their resistivity is much larger than 10~~ohm-cm and formation of the p-n junction or Schottky barrier is imposible. A simple method to characterize deep levels in high-resistivity GaAs was reported for the transient photocurrent analysis (optical DLTS) (7). It is the purpose of the present paper that we apply this optical DLTS method to the high resistivity I chalcogenide materials, and investi& o & gate the concentration and energy C a a U & 0 levels of gap states by the optical u o a~ @ DLTS analysis. Moreover, we present 3 @ an approximation method applied to the optical DLTS method, since the photocurrent decay of the chalcogenide is not given by the equation of exp(-At) (8). Experimental.Figure 1 shows the schematic diagram of the experiment. Electron-hole pairs can be generated by using a monochromatic light (100 pw/cm2) . In high-resistivity chalcogenide materials, carriers cannot be easily injected by electrical &I means. So, in the optical DLTS methtime t od, they are optically generated in Fig.1 Schematic diagram. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814131