Optical Time-of-Flight Investigation in Ambipolar Carrier Transport in Specially Designed GaAs/GaAlAs Quantum Well Structures

Abstract

Today the high frequency properties of semiconductor devices are essential for fast computer and fast communication systems. The cutoff frequency of such devices is substantially determined by the transit times and velocities in all involved layers. The most direct approach to these transport properties is obtained by Time-of-Flight (TOF) experiments, in which one derives the carrier velocity for measurements of the flight duration over different known distances. Hence the results critically depend on the accuracy with which the transit time and distance can be measured. Recently,different optical techniques have been developed to increase the time resolution in relation to electrical TOF studies. In particular,carrier-induced reflectivity changes [1] and nonlinear luminescence [2] have been used to probe the carrier movement. The penetration depth of the light and the focus diameter, respectively, limit the spatial resolution of these experiments.

We present a new all—optical time-of-flight method capable of high spatial and temporal resolution. Transport properties are provided from measurements of the flight duration between two quantum wells sandwiching a semiconductor transport layer.