Excitation‐dependent carrier dynamics in Al‐rich AlGaN layers and multiple quantum wells

Abstract

The combined temporally, spatially and spectrally-resolved optical techniques, namely the photoluminescence, light induced transient grating, and differential reflectivity were used for investigation of excitation-dependent PL efficiency, exciton lifetime, and diffusion coefficient in Si-doped Al-rich multiple quantum wells and epilayers at various temperatures. Novel features of carrier recombination and in-plane diffusion were observed. Low-excitation radiative lifetime of 1-2 ns was found temperature-independent in 80-150 K interval, while it sublinearly decreased with excitation at excess carrier densities above 10 18 cm À3 . The lifetime decrease correlated with the increase of diffusion coefficient, indicating excitation-enhanced delocalization of localized excitons and therefore enhanced capture to nonradiative centers. The droop of photoluminescence efficiency with excitation was the strongest at 80-150 K due to strong delocalisation at low-temperatures, while at higher temperatures the thermal activation prevailed in photoluminescence excitation dependence. The photoluminescence efficiency quenching at T > 200 K provided rather high activation energies of $100 and 160 meV for Al-rich multiple quantum wells and epilayers, correspondingly.

Impacts of Si-doping on vacancy complex formation and their influences on deep ultraviolet luminescence dynamics in AlxGa1−xN films and multiple quantum wells grown by metalorganic vapor phase epitaxy

“…Due to the limited availability of desirable femtosecond excitation sources operated at DUV wavelengths, only several papers have dealt with the emission dynamics of (Al,Ga)N in the UV-C range. 21,48,67,[95][96][97][98][99][100][101][102][103][104] The authors have been studying the recombination dynamics of excitons and/or free carriers in UID AlN and Al x Ga 1−x N alloys using TRPL 96) and time-resolved cathodoluminescence (TRCL) measurements. 91,97,98) For the TRPL measurement, approximately 200 fs pulses of a frequency-quadrupled ( w 4 ) mode-locked Al 2 O 3 :Ti laser were used as the excitation source.…”

“…Accordingly, direct measurement of t minority and spatially resolved luminescence measurement should be carried out on the AlGaN wells. However, because of the limited availability of femtosecond pulsed lasers applicable at DUV wavelengths, few groups have dealt with 21,48,67,[95][96][97][98][99][100][101][102][103][104] the emission dynamics of WBG AlN and Al x Ga 1−x N alloys of high x. Nonetheless, the importance of localization and delocalization of excitons has been discussed for DUV light-emitting Al x Ga 1−x N QWs.…”

“…Nonetheless, the importance of localization and delocalization of excitons has been discussed for DUV light-emitting Al x Ga 1−x N QWs. 98,[100][101][102][103] Lefebvre et al 102) and Scajev et al 103) have discussed the luminescence dynamics of localized excitons in Al x Ga 1−x N/Al y Ga 1−y N MQWs grown by the same group of Refs.86 and 93, by changing the measuring temperature and excitation power. However, either the atomistic origin of NRCs or Si-doping effects has not been assessed.…”

“…However, either the atomistic origin of NRCs or Si-doping effects has not been assessed. [102][103][104] Understanding the physics underlying the Si-doping effect may offer an insight into a way of increasing h int NBE of Al x Ga 1−x N DUV light-emitters. In this progress review, the results of time-resolved photoluminescence (TRPL) and spatio-time-resolved cathodoluminescence (STRCL) [105][106][107][108][109][110][111] measurements on the NBE emission of Al 0.6 Ga 0.4 N films 86) doped with Si at various concentrations ([Si]) and Al 0.68 Ga 0.32 N/Al 0.77 Ga 0.23 N MQWs 85) doped with Si at different out-of-plane locations of the structures are summarized to discuss 48,91) the impacts of V III formation on t minority in the weak excitation regime.…”

Spatio-time-resolved cathodoluminescence studies of wide-bandgap group-III nitride semiconductors

“…Therefore, direct measurement of the emission dynamics of AlGaN wells is mandatory. However, owing to the limited availability of femtosecond lasers applicable at DUV wavelengths, 24,25,28,29,101,142,143,145,[157][158][159][160][161][162] few groups have dealt with 24,25,28,29,37,42,101,[157][158][159][160][161][162] the emission dynamics of WBG AlN and high-x Al x Ga 1-x N alloys. Nevertheless, the importance of localization and delocalization of excitons has been pointed out for DUV light-emitting Al x Ga 1-x N QWs.…”