Influence of growth temperature on carrier localization in InGaN/GaN MQWs with strongly redshifted emission band

To shift the emission band to long wavelength side, InGaN/GaN multiple quantum wells were grown by metalorganic chemical vapor deposition (MOCVD) using pulsed delivery of the metalorganic precursors at fixed parameters of the pulses but variable growth temperatures and by introducing short-period superlattices (SPSL) as buffer layers. By decreasing the growth temperatures for both SPSL and quantum wells down to 800°C, a considerable shift of the photoluminescence (PL) band peak down to ~2eV is achieved at reasonably acceptable decrease in PL intensity at low carrier density. However, increase in the carrier density resulted in considerable blue shift of the band, and the efficiency droop onset occurred at rather low carrier densities. The comparison of the data on PL and differential optical transmittance, which were supported by structural analysis, revealed that the large red shift in the PL band position is predominantly caused by an increasing tail of localized states. Meanwhile, the efficiency droop effect in the samples under study is caused predominantly by the enhancement of nonradiative carrier recombination.