New technique for measuring carrier mobility using a modified boxcar integrator

Abstract

A new technique for measuring the drift carrier mobility is described. A boxcar integrator was modified to enable a delay-time scan using simple decimal counters. The transient photocurrent was integrated repeatedly using the modified boxcar integrator. After simple signal processing, the original photocurrent was recovered with enhanced signal to noise ratios. The hole mobility of a 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) thin film was measured using the new method. The mobility of NPB under an electric field as low as 2.5 x 10(4) V cm(-1) was calculated to be 5.84 x 10(-4) cm(2) V-1 s(-1). This method may be a useful measurement technique when either the electric field or signal to noise ratio is very low. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3226886]