Full wafer optical characterisation of resonant tunnelling structures using photoluminescence excitation spectroscopy

We report on a novel optical technique for accurately characterising unprocessed GaAs/AlGaAs tunnelling structures having two or more thin barriers and thick, heavily doped, contact layers. The results from photoluminescence excitation spectroscopy measurements are presented in which the intensity of the photoluminescence from the heavily doped contact layers rather than photoluminescence from the quantum wells is monitored. This method gives essential information for growth and quality control of "as-grown" layers prior to device fabrication. The usefulness and precision of this technique is illustrated by the measurement of a 0.3% variation in layer thickness from the centre to the edge of an as-grown wafer, and a 1% wafer to wafer variation in layer thickness in a series of triple barrier resonant tunnelling structures that have been designed for use at THz frequencies.