Time-resolved cathodoluminescence

Abstract

Advent of new semiconductors calls for a nano scale characterization tool that provides spatial, temporal and spectral data simultaneously to study the optical and structural properties. A new time resolved CL measurement system (TRCL) with spatial resolution of 50 nm and temporal resolution of 750 ps is developed. The design is based on sequential registration technique using gated intensified charge coupled device (ICCD) as time resolving photo detector sensitive in a spectral range from 165 nm to 820 nm.

The surface recombination affect in a GaAsP light emitting diode (LED) with nitrogen doping is studied using a short excitation pulse and shown that the surface recombination leads to a non exponential region during the early parts of the decay. It is also shown that the effective minority carrier life decreases as the defect site is approached indicating the non radiative recombination at the vicinity of defect site. The radiative recombination mechanisms at varying excitation conditions is studied and demonstrated that the radiative recombination increases with the excitation intensity and non radiative Auger recombination becomes dominant at higher level of excitation.

The influence of growth conditions on threading dislocations (TDs) and indium surface segregation at the well/barrier interface in InGaN/GaN quantum dots (QDs) is studied. It is demonstrated that the effective lifetime decreases towards the TD core indicating that non radiative recombination becomes predominant when approaching a dislocation. The lifetime variations in various samples prepared at different growth conditions show sample with low indium composition QDs and indium segregation to the interface layers exhibit lower minority carrier lifetime due to carriers drift towards non radiative defects generated due to strain. This leads to lower luminescence efficiency.