Photoluminescence temperature behavior and Monte Carlo simulation of exciton hopping in InGaN multiple quantum wells

Abstract

Application of Monte Carlo simulation of exciton (carrier) hopping for the analysis of the photoluminescence (PL) temperature behavior in In 0.2 Ga 0.8 N/GaN multiple quantum wells is reported. The PL linewidth and peak position measured in the 10-300 K range exhibited a W-shaped and S-shaped temperature behavior, respectively. The W-shaped linewidth dependence was fitted with the results of Monte Carlo simulation, which involved phonon-assisted exciton hopping through energy states confined in the band potential fluctuation minima. The simulation yielded the values of the standard deviation for potential fluctuations within In-rich regions (31 meV), dispersion of the average exciton energy in different regions (29 meV), and the temperature dependence of the band gap, which was found to be in a fair agreement with the photoreflectance data. Our results, which infer in-plane motion of localized excitons within the wells, are consistent with the model of large In-rich regions ("segmented quantum wells" or "quantum discs") with band potential fluctuations inside these regions. 1 Introduction InGaN/GaN multiple quantum wells (MQWs) are known to efficiently emit green to near UV light in spite of high density of dislocations due to lattice-mismatched substrates [1]. The unique optical properties of InGaN are believed to relate to compositional disorder. In particular, carrier and exciton localization in the band potential fluctuation minima should prevent them from reaching nonradiative recombination sites. However despite a commercial success of nitride-based emitters, the physical origin of efficient light generation in this partially disordered system is unveiled incompletely. In particular, carrier/exciton motion and the establishing of their distribution over the localized states in InGaN are not completely understood. Meanwhile, an anomalous temperature behavior of photoluminescence (PL) in group-III nitride structures designated as an S-shaped peak position dependence and Wshaped linewidth dependence [2][3][4] indicate that exciton/carrier motion occurs via phonon-assisted tunneling (hopping) through localized states [5,6], what results in incomplete thermalization of localized excitons at low temperature. Recently, an evolvement of the S-shaped and W-shaped temperature dependences of the PL peak position and linewidth, respectively, was observed with gradual incorporation of indium in to AlGaN alloy and accounted for by using Monte Carlo simulation of exciton hopping [7].Here we show that phonon-assisted hopping can account for nonmonotonous temperature dependences of the PL peak position and linewidth in InGaN MQWs. The PL linewidth temperature behavior is shown to be in quantitative consistence with the energy of the fundamental optical transition deduced from the photoreflectance (PR) measurements [8].

GaInN quantum well design and measurement conditions affecting the emission energy S‐shape

“…The S-shape behaviour has already been studied extensively [1][2][3][4][5]. Theoretical models based on charge carrier localization, the temperature dependent occupation of band tail states, and hopping processes between localized states describe the S-shape quite well [2,3,6]. In most studies, experimental and theoretical results feature stronger S-shape behaviour when band gap variations or fluctuations are increased as a consequence of locally varying indium concentration or QW width.…”

Energy Scaling of Compositional Disorder in Ternary Transition‐Metal Dichalcogenide Monolayers

“…Let us consider first the PL features that are observed in the ternary Mo 0.3 W 0.7 Se 2 alloy system and not observed in its binary counterparts MoSe 2 and WSe 2 , that is, the non-monotonous temperature dependence of the PL peak energy and that of the PL linewidth at temperatures close to T ≈ 60 K. Nagler et al, [92] who recently observed analogous PL effects in the MoSe 2 -WSe 2 heterostructure, noted that such non-monotonous temperature dependences are qualitatively similar to the temperaturedependent behavior of the excitonic emission energy and of the emission linewidth in disordered bulk semiconductors and quantum wells. [64,[97][98][99][100] Indeed, such effects have been observed in numerous studies of the exciton PL in quantum wells manufactured from multicomponent III-V semiconductors [64,65,70,[72][73][74]91,[97][98][99][101][102][103][104][105][106][107] and in arrays of quantum islands manufactured from II-VI and III-V semiconductors. [71,[108][109][110] Already in the pioneering studies of the S-shape in the temperature-dependent Stokes shift by Skolnick et al [64] and by Davey et al [65] this effect was attributed to the redistribution of excitons in the manifold of localized states created by the disorder potential, as illustrated in Figure 5a.…”

“…Several studies have evidenced localization of excitons by a disorder potential in TMDs. [92,[111][112][113][114][115][116] Therefore, one can expect the disorderinduced S-shape for the T-dependence of the PL peak energy ε PL (T) illustrated in Figure 5b [64,65,[70][71][72][73][74]91,[97][98][99][101][102][103][104][105][106][107][108][109][110] is often accompanied by the non-monotonous T-dependence of the PL linewidth Γ PL (T) schematically illustrated in Figure 5c. [65,70,71,73,[97][98][99]103,106] The latter effect can be recognized in Figure 3c for Mo 0.3 W 0.7 Se 2 yielding the value T 2 ≃ 60 K. Since the ternary system demonstrates the PL effects observed previously in disordered 2D semiconductors, while the binary TMDs are free from such effects, as depicted in Figures 2a,b and 3a,b, let us consider a possible physical mechanism for disorder effects in more detail, aiming to reveal the origin of disorder in the TMD Mo 0.3 W 0.7 Se 2 alloy.…”

“…In Monte Carlo simulations of exciton dyna mics, [69][70][71][72][73][97][98][99][103][104][105] a random distribution of the localization sites with the 2D concentration N was assumed and two particular energy distributions of the disorder-induced DOS (or their combinations) were considered, the exponential DOS…”

Investigation of localization effect in GaN-rich InGaN alloys and modified band-tail model

“…In particular, In x Ga 1−x N alloys are very promising, because they have a tunable direct bandgap varying from 0•7 to 3•42 eV, which makes In x Ga 1−x N alloy a key material in fabricating GaN-based blue light emitting diodes (LEDs) and laser diodes (LDs). So far, temperature-dependent optical properties of In x Ga 1−x N alloys have been investigated by several groups (Shan et al 1995(Shan et al , 1996(Shan et al , 1998Smith et al 1996;Eliseev et al 1997;Narukawa et al 1997;Cho et al 1998;Schenk et al 2000;Wang et al 2000;Li et al 2001;Cao et al 2003;Chung et al 2003;Ramaiah et al 2004;Wang et al 2004;Yu et al 2004;Cheng et al 2005;Kazlauskas et al 2005;Na et al 2006;Usov et al 2007;Chang et al 2009;Zhao et al 2012a). However, very few systematic investigations on temperature-dependent photoluminescence (PL) properties of GaN-rich In x Ga 1−x N alloys have been reported.…”