Effect of carrier confinement on effective mass of excitons and estimation of ultralow disorder in Al x Ga1−x As/GaAs quantum wells by magneto-photoluminescence

Abstract

Effect of charge carrier confinement and ultra-low disorder acquainted in AlGaAs/GaAs multi-quantum well system is investigated via Magneto-photoluminescence spectroscopy. Significant increase of effective mass is observed for the confined exciton in narrow QWs. The foremost reason behind such an observation is due to the induced non-parabolicity in bands. Moreover, as the thickness of the QW are reduced, confined excitons in QW experience atomic irregularities at the hetero-junctions and their effects are prominent in the photoluminescence linewidth. Amount of photoluminescence line-broadening caused by the atomic irregularities at the hetero-junctions is correlated with average fluctuation (δ 1) in QW thickness. The estimated δ 1 for Al0.3Ga0.7As/GaAs QWs are found to be ±(0.14 − 1.6)× ‘one monolayer thickness of GaAs layer’. Further, the strong perturbations due to magnetic field in a system helps in realizing optical properties of exciton in QWs, where magnetic field is used as a probe to detect ultralow defects in the QW. Additionally, the influence of magnetic field on the free and bound exciton luminescence is explained by a simple model. The proposed approach for measuring the interface and volume defects in an ultra-low disordered system by Magneto-PL spectroscopy technique will be highly beneficial in high mobility devices for advanced applications.

Broad Tunability of Carrier Effective Masses in Two-Dimensional Halide Perovskites

“…The energy separation of the Landau levels provides a direct handle for the reduced effective mass of the charge carriers, μ, in 2D halide perovskites. Combining our measurement results with first-principles calculations, we find that μ can be tuned from a very low value of 0.05 to 0.15 by metal composition, which is a much wider range than that previously reported in 3D perovskites. ,− Furthermore, we observe that the effective mass in 2D halide perovskites can be even lower than in the corresponding bulk material, which is in striking contrast to what is known for classic epitaxial quantum wells. − Our direct experimental approach to determine the effective mass together with our theoretical calculations render a broader perspective on the available ways to modify effective mass in this fascinating material system.…”

“…Remarkably, in the case of (PEA) 2 SnI 4 the value μ is further reduced to 0.055 and is clearly even less than in the tin-based 3D perovskite FASnI 3 (0.102). Such low effective masses for PEA-based 2D halide perovskites is in contrast to what is known for fully inorganic epitaxial quantum wells, where quantum confinement effects lead to an enhanced effective mass due to both the nonparabolicity of the conduction band and the wave function penetration into the barrier material. − Our results show that the mechanism controlling the in-plane band dispersion in 2D halide perovskites is different and strongly depends on the ionic composition of the material, thus allowing for a broad tunability of the effective mass.…”

Tuning the Excitonic Properties of the 2D (PEA)2(MA)n−1PbnI3n+1Perovskite Family via Quantum Confinement

“…Although the effective mass μ indeed approaches the value for bulk MAPbI 3 (Figure h), the increase in μ with increasing n is in striking contrast to what is known for fully inorganic epitaxial quantum wells − and BA-based 2D perovskites, where the reduction of quantum well width leads to an enhancement of μ. The experimentally observed trend is also in contrast to the theoretically estimated behavior for PEA-containing 2D perovskites, where the μ is reduced while n increases, very similar to the BA case .…”

Scaling law for excitons in 2D perovskite quantum wells

“…The limiting 3D value is thus expected to be reached for larger n -value, i.e., when the RPP bandgap equals the 3D perovskite one. Furthermore, electronic band mixing and non-parabolicity effects have been known to induce changes in the exciton reduced mass in quantum well systems 32–35 . These effects have also been discussed in classic inorganic semiconductors and agree with the n -value dependence of the experimental bandgap, diamagnetic shift and g -factor (Figs.…”