Modulation speed and leakage current in 650 nm resonant-cavity light emitting diodes

The authors have investigated red-emitting (650 nm) resonant-cavity light emitting diodes for use with polymer optical fibres. The small signal modulation response is characterised by a single order roll-off. The -3 dB bandwidth is found to be determined solely by the differential carrier lifetime, τ, in the active region and hence dependent on current density, J, alone with no intrinsic size effects. The τ(J) relation allows the calculation of the active region carrier density and hence the recombination parameters (mono- and bimolecular) in the regime where the leakage is small. It is shown that the leakage is insignificant for currents below 200 A/cm² at 20°C. Above 40°C the leakage rises rapidly with temperature, and is evident from a dramatic fall in τ and an accelerated rise in the current required to maintain constant light output.