High resolution measurement of localized-state distributions from transient photoconductivity in amorphous and polymeric semiconductors

Abstract

The energy resolution of a method for measuring localized-state distributions in amorphous and polymeric semiconductors has been improved in terms of Tikhonov regularization. The method is based on the analysis of transient photoconductivity data using Laplace transforms, and is valid for both pre- and postmonomolecular recombination regimes of the transient photoconductivity. The improvement of the energy resolution is shown using transient photoconductivity data numerically generated from model localized-state distributions appropriate for the materials. In addition, the measurement of localized-state distributions from time-of-flight transient photocurrents is examined. The applicability of the method with improved energy resolution is demonstrated for undoped hydrogenated amorphous silicon, poly(para-phenylene vinylene) and poly(methylphenylsilane).

New insights on traps states in organic semiconductor applying illumination-free transient current method

“…This current decreases with time due to the immobilization of carriers by trapping. With an appropriate transformation of the current in region III, the DOS as a function of energy can be estimated from both types of measurements [15][16][17]. For TOF measurements, the mobility of the fastest carriers can be additionally estimated from the transit time.…”

Analysis of Trap Distribution Using Time-of-Flight Spectroscopy

“…(14) was as follows. [11][12][13] A derivative of eq. (14) with respect to gives the relation dð1 À~ ðsÞÞ=d ¼ À R d" ð"Þ f ð"; Þ, where f ð"; Þ ¼ ðk B TÞ À1 e Àð"ÀÞ=ðk B TÞ =½1 þ e Àð"ÀÞ=ðk B TÞ 2 .…”

Probing localized states distributions in semiconductors by Laplace transform transient photocurrent spectroscopy

“…Then the last expression can be written in terms of the initial value of the photocurrent 7 (Naito H. et al, 1996;Nagase T. et al, 1998Nagase T. et al, , 1999.…”

“…Here we present a further alternative method for inverting I-t, based on the use of Tikhonov regularization to solve equation 2.6, which is a Fredholm integral of the first kind. It has previously been shown (Nagase et al, 1999) that this approach is capable of high resolution and improved noise immunity over other methods when used to solve the general system of multiple-trapping rate equations in the ^-domain.…”