Novel Picosecond Time-Resolved Cathodoluminescence to Probe Exciton Recombination Dynamics in GaN and GaN Based Heterostructures

Picosecond and femtosecond spectroscopy allow a detailed study of carrier dynamics in nanosctructured materials [1]. In such experiments, a laser pulse usually excites several nanostructures at once. However, spectroscopic information may also be acquired using pulses from an electron beam in a modern scanning electron microscope (SEM), exploiting a phenomenon called cathodoluminescence (CL). This approach offers several advantages. The multimode imaging capabilities of the SEM enable the correlation of optical properties (via CL) with surface morphology (secondary electron mode) at the nanometer scale [2]. The large energy of the electrons allows to excite wide-bandgap materials. Here, we present results obtained with an original timeresolved cathodoluminescence (TRCL) setup [3]. This setup uses ultrafast UV laser pulses to create short photoelectron pulses. The laser pulses illuminate a metal photocathode from which the electrons are extracted and accelerated inside the electro-optical column of the microscope and focused on the sample surface. The collected CL signal is analyzed in a spectrometer and in an ultrafast camera (STREAK camera) to obtain high time resolution.