Abstract
The combination of time-resolved (TR) and power-dependent relative (PDR) photoluminescence (PL) measurements reveals the possibility of separating the radiative and non-radiative minority carrier lifetimes and measuring the sample-dependent effective radiative recombination coefficient in direct bandgap semiconductors. To demonstrate the method, measurements on 2 μm thick p-type GaAs double-hetero structures were conducted for various doping concentrations in the range of 5x1016 and 1x1018 cm-3. With a photon recycling factor of 0.76 ± 0.04 the radiative recombination coefficient was determined to be (3.3±0.6)×10-10 cm3s-1 for the structures with a doping concentration below 1*1018 cm-3, whereas the effective radiative recombination parameter for an absorber thickness of 2 μm was directly measured to be (0.78±0.07) ×10-10 cm3s-1. For a doping concentration of 1×1018 cm-3, the radiative recombination coefficient decreases significantly probably due to the degeneracy of the semiconductor.
Highlights
Photon recycling within the active layer is effectively increasing the minority carrier lifetime associated with the radiative recombination process τeraffd
The decay of the photoluminescence signal was measured by time-resolved photoluminescence (TR-PL) for different laser intensities, which are equivalent to different excess carrier densities ∆n
The signals measured at low injection are all monoexponential, whereas the analysis of non-monoexponential decays would need special attention.11,13,17. At these low excitation densities, the monoexponential time constant is assumed to be equivalent to the effective bulk minority carrier lifetime; this assumption will be tested later when comparing the extracted effective radiative recombination coefficient to that calculated from theory
Summary
It has recently been shown that photon recycling must be considered for the modelling of highly-efficient optoelectronic devices. Photon recycling within the active layer is effectively increasing the minority carrier lifetime associated with the radiative recombination process τeraffd. This is often taken into account by introducing a photon-recycling factor f.4 Other authors have included this factor in defining an effective radiative recombination coefficient as shown in equation (1), where N denotes the activated dopant density and ∆n denotes the excess carrier density in this context. All steady-state measurement methods for radiative efficiency face the challenge of calibration as they are not absolute This is solved by the assumption of pure radiative recombination at high injection or low temperature, which is only valid for certain samples. The mono-exponential behavior of the PL decay combined with our estimated initial carrier density suggest that the excess carrier density is significant compared to the shallow metastable trap states; this is confirmed by the agreement between the extracted and calculated values of Beraffd. This renders the decay lifetime as approximately representative of the effective bulk lifetime
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