Amorphous Silicon Crystalline Silicon Heterojunction Solar Cells by Wolfgang Rainer Fahrner

Author:Wolfgang Rainer Fahrner
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

6.4.4 Deep-Level Transient Spectroscopy

Deep-level transient spectroscopy (DLTS) is a technique for monitoring and characterizing deep levels introduced intentionally or occurring naturally in a-Si:H. In particular, the method can determine the activation energy of a deep level, its capture cross section and concentration, and can distinguish between traps and recombination centers.

The DLTS technique is mostly used to observe the thermal emission from majority carrier traps, which can be recorded as a capacitance or voltage transient. The basic principle of a DLTS measurement is as follows. The bias on a diode is pulsed between a bias near zero and some reverse bias V R with a repetition time t r as shown in Fig. 41a. The zero bias condition is held for a time t f during which the traps are filled with majority carriers in this interval the capacitance signal contains no useful information and the instrument may be overloaded by the high zero bias capacitance. During the reverse bias pulse, the trapped carriers are emitted at a rate e n producing an exponential transient in the capacitance, which in its general form can be written as

Fig. 41Diagram indicating the principle of a DLTS measurement: Part (a) illustrates the repetitive filling and reverse bias pulse sequence, and part (b) shows the diode capacitance transient, as a function of time. Part (c) indicates the variation of the transient time constant τ (=e n −1) with reciprocal temperature for two different traps, and Part (d) illustrates the deep-level transient spectrum that is produced by a rate window with reference time constant τref operating on the capacitance transient shown in (b)

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.