Abstract

Time Correlated Single Photon Counting (TCSPC), using solid state single photon avalanche diodes (SPADs) as detectors, has for some time been the most successful method of measuring time resolved photoluminescence (TRPL) in the near infra red region of the spectrum (Figure 1). However, the longest wavelength hitherto measurable in this way was ~1460nm, using a Ge SPAD cooled to 77K^[1], thus excluding from study the materials and devices designed to operate at wavelengths between 1500nm and 1600nm, for long haul fibre-based telecommunications applications. InGaAs lattice-matched to InP is an ideal material for low noise optical absorption at wavelengths up to ~1600nm, but inter-band tunneling under high electric fields prevents its sole use in the construction of a standard p-n junction SPAD. Recent developments in the manufacture of InGaAs/InP separate absorption, grading, and multiplication layer avalanche photodiodes, in which the avalanche multiplication process takes place in the InP layer, have resulted in the realisation of a SPAD which exhibits dark count rates of -10s^-1, detection efficiencies of ~13%, and timing jitter ~300ps when operated at 77K. This SPAD has now been incorporated into a TRPL microscope to measure the carrier lifetime of an InGaAsP multiple quantum well structure, with an emission wavelength of 1525nm, and thus reach for the first time into the second telecommunications window. Initial measurements of the (295K) recombination lifetime for the 10nm width quantum wells provide a value of 26±1ns (Figure 2). We will present our latest data from this and similar samples, along with details of the detector and microscope that have been used to acquire them, and discuss the performance-limiting factors in these new measurements.

© 2000 IEEE