Transition of radiative recombination channels from delocalized states to localized states in a GaInP alloy with partial atomic ordering: a direct optical signature of Mott transition?

Abstract

Anderson localization is a predominant phenomenon in condensed matter and materials physics. In fact, localized and delocalized states often co-exist in one material. They are separated by a boundary called the mobility edge. Mott transition may take place between these two regimes. However, it is widely recognized that an apparent demonstration of Anderson localization or Mott transition is a challenging task. In this article, we present a direct optical observation of a transition of radiative recombination dominant channels from delocalized (i.e., local extended) states to Anderson localized states in the GaInP base layer of a GaInP/GaAs single junction solar cell by the means of the variable-temperature electroluminescence (EL) technique. It is found that by increasing temperature, we can boost a remarkable transition of radiative recombination dominant channels from the delocalized states to the localized states. The delocalized states are induced by the local atomic ordering domains (InP/GaP monolayer superlattices) while the localized states are caused by random distribution of indium (gallium) content. The efficient transfer and thermal redistribution of carriers between the two kinds of electronic states was revealed to result in both a distinct EL mechanism transition and an electrical resistance evolution with temperature. Our study gives rise to a self-consistent precise picture for carrier localization and transfer in a GaInP alloy, which is an extremely technologically important energy material for fabricating high-efficiency photovoltaic devices.

Investigation of Localized States in GaAsSb Epilayers Grown by Molecular Beam Epitaxy

“…This unusual temperature dependence of the PL peak significantly deviated from that predicted by Varshni or Bose-Einstein formula 33 , revealing the existence of localized states in the GaAsSb epilayers. The PL spectra of sample 3 exhibit a broadening peak, and two emission peak exist at 40 K. Based on the previous reported results 32 , the high energy peak is related to the band to band emission, and the low energy peak is related to localized state because it is far away from the conduction band edge.…”

“…Peak A displays a low energy shoulder at 10 K, which was due to the distribution of carriers at different emission states. It is interesting that the PL spectra of sample 2 (peak B) exhibit a typical ‘S’ shape behavior 30 31 32 . The peak B had a trend of redshift first, and then blueshift, finally redshift again (at around 80 K) as the temperature continuously increases.…”

2D Carrier Localization at the Wurtzite-Zincblende Interface in Novel Layered InP Nanomembranes

“…To analytically interpret the abnormal peak shift of the type II transition, the localized-state ensemble (LSE) luminescence model developed by Li and Xu is employed. , The LSE model has been widely used to quantitatively describe the state filling and thermal transfer of localized carriers in semiconductors. − By adding a modification term to the Varshni’s empirical formula, the luminescence peak position of localized carriers can be formulated as where θ is the Debye temperature, i.e., 425 K for InP, α is the Varshni parameter, and x is a dimensionless parameter for the thermal redistribution of localized carriers, which can be obtained by numerically solving the following equation where σ is the distribution of the localized states, Δ E is characteristic energy of the depth of the trap, and τ tr ( τ r ) represents the time constant of carrier escaping (radiative recombination) from the localized states.…”

A generalized model for time-resolved luminescence of localized carriers and applications: Dispersive thermodynamics of localized carriers

“…is a ubiquitous phenomenon which was theoretically treated by Anderson for the first time 1 . To date, CL and related phenomena still remain as a subject of extensive interest primarily because of their scientific significance and profound impact on electrical, magnetic and optical properties of material systems 2–18 . With the rapid development of the InGaN alloy based blue-green light emitting diodes, recently, the CL effect induced by structural imperfections has been increasingly addressed 19–21 .…”