Exciton radiative decay time

Figure 11. Dependence of the exciton radiative decay time on the effective radius, a, at 10 K (open circles) and 77 K (closed circles). A solid line represents theoretical calculation from Eq. (10). (Taken from reference 58 with permission.)...

Carrier and exciton dynamics in InGaN/GaN MQWs have also been studied at a high optical pumping power [34], At 7 K, a radiative decay lifetime of 250 ps was observed for the dominant transition at a generated carrier density of 1012/cm2. The time-resolved measurement showed that the decay of PL has a bimolecular recombination characteristic. At room temperature, the carrier recombination was found to be dominated by non-radiative processes with a measured lifetime of 130 ps. Well width dependence of carrier and exciton dynamics in InGaN/GaN MQWs has also been measured [35]. The dominant radiative recombination at room temperature was attributed to the band-to-band transition. Combined with an absolute internal quantum efficiency measurement, a lower limit of 4 x 10 9 cm3/s on the bimolecular radiative recombination coefficient B was obtained. At low temperatures, the carrier... 

Integrating this equation over energy, adding the density of excitons that still reside in parent" host molecules, and accounting for the radiative decay of excitons yields the total density pft) of excitons occupying intrinsic sites at the time t ... 

In the last decade the Wannier exciton emission from direct band gap soniconductors was reconsidered for high count-rate and coincidence-detection scintillation applications and Cul, Hglj, Pbl2, ZnO Ga, and CdS In compounds in powder form were studied (Derenzo et al. 2002). In direct gap semiconductors a favorable combination of a smaller gap and an UV-VIS emission center based on Wannier exciton can provide high scintillation efficiency and subnanosecond radiative lifetimes due to microscopic superradiance effect (Niki 2006, Wilkinson et al. 2004). On the other hand, the Stokes shift of such emission centers is necessarily low (typically below 0.1 eV) and it prevents their usage in the bulk form due to enhanced reabsorption effect, see Figure 4.4. The ZnO Ga has shown the best combination of subnanosecond decay time and emission intensity... 

Decay Decay time ns to 150 ps from blue to red increases at low temperature due to singlet-triplet exciton state splitting (Cullis et al. 1997 Bisi et al. 2000) Depends on quantum confinement strength (effect on wavelength) and surface passivation (limited by non-radiative recombinations) (Cullis et al. 1997 Bisi et al. 2000)... 

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