Two Distinct Origins of Highly Localized Luminescent Centers within InGaN/GaN Quantum‐Well Light‐Emitting Diodes

Abstract

The high light‐output efficiencies of InxGa1‐xN quantum‐well (QW)‐based light‐emitting diodes (LEDs) even in presence of a large number of nonradiative recombination centers (such as dislocations) has been explained by localization of carriers in radiative potential traps, the origins of which still remain unclear. To provide insights on the highly efficient radiative traps, spectrally resolved photoluminescence (PL) microscopy has been performed on green‐light‐emitting In0.22Ga0.78N QW LEDs, by selectively generating carriers in the alloy layers. PL imaging shows the presence of numerous inhomogeneously distributed low‐band‐gap traps with diverse radiative intensities. PL spectroscopy of a statistically relevant number of individual traps reveals a clear bimodal distribution in terms of both band‐gap energies and radiative recombination efficiencies, indicating the presence of two distinct classes of carrier localization centers within the same QW sample. Disparity in their relative surface coverage and photoemission “blinking” characteristics suggests that the deep traps originate from local compositional fluctuations of indium within the alloy, while the shallow traps arise from nanometer‐scale thickness variations of the active layers. This is further supported by Poisson–Schrödinger self‐consistent calculations and implies that radiative traps formed due to both local indium content and interface‐morphology‐related heterogeneities can coexist within the same QW sample.

Influence of InGaN growth rate on the localization states and optical properties of InGaN/GaN multiple quantum wells

“…In addition, when the Equation (1) is used to fit P L and P H individually, there are two different band gaps with the respective band tail states for P L and P H because of the different average indium content. Actually, it has been also demonstrated by De et al [26,27] that two distinct classes of carrier localization centers exist in InGaN/GaN MQWs. The deep traps and the shallow traps originate from local compositional fluctuations of indium content and thickness variation of the active layers, respectively.…”

Pseudohalide (SCN–)-Doped MAPbI3 Perovskites: A Few Surprises

“…We note that much smaller amplitude intensity fluctuations, higher than the background noise due to CCD (in absence of the crystals, Figure S9, SI) are present throughout the crystal (marked 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 17 While photoinduced blinking behaviors are commonly observed for single semiconductor nanocrystals and fluorescent molecules [30][31] , and has also been reported for individual radiative recombination centers in quantum-well heterostructures 26,[32][33] , untill recently, PL intermittency has been rarely observed in perovskite microcrystals 34 . While there are a couple of reports on relatively large (~µm) emissive domains within InGaN quantum-well heterostructures undergoing opitcal instability [32][33] , these observations are uncommon, and it is quite surprizing that such a high density of local sub-microscopic dominains within these perovskite crystals of several micrometers exhibits such unambiguous PL intremittency.…”

“…A narrow slit was used to spatially-resolve the emission along a vertical strip of an isolated crystal as depicted in Figure 5a, following which the dispersed emission spectra of the entire strip (Figure 5b) was collected simultaneously using a transmission grating based spectrograph coupled to a CCD detector [26][27] . The difference in emission behaviours, both at the boundaries as well as interior of the micro-crystal were exemplified by representative spectral profiles in Figure 5c, and are compared with the spatially averaged emission spectra.…”

Temperature-dependent photoluminescence in light-emitting diodes

“…The PL technique is also a powerful and important tool for obtaining information regarding low-dimensional semiconductors, e.g., quantum-size effects91011, many-body processes1213, strain analysis141516, localized states1718192021, excitonic states2223, coupling effects2425, carrier relaxation processes and recombination mechanisms262728293031. Because of the importance of luminescence phenomena, it is vitally important to be able to conduct a careful analysis of the process itself, including the generation, transport and recombination of carriers.…”