Determination of recombination coefficients for nanocrystalline silicon embedded in hydrogenated amorphous silicon

Mid-infrared photoluminescence revealing internal quantum efficiency enhancement of type-I and type-II InAs core/shell nanowires

Internal quantum efficiency (IQE) is an important figure of merit for photoelectric applications. While the InAs core/shell (c/s) nanowire (NW) is a promising solution for efficient quantum emission, the relationship between the IQE and shell coating remains unclear. This Letter reports mid-infrared PL measurements on InAs/InGaAs, InAs/AlSb, and InAs/GaSb c/s NWs, together with bare InAs NWs as a reference. Analyses show that the IQE is depressed by a shell coating at 9 K but gets improved by up to approximately 50% for the InGaAs shell coating at 40 -140 K and up to approximately 20% beyond 110 K for the AlSb shell. The effect is ascribed not only to the crystal quality but more importantly to the radial band alignment. The result indicates the high-temperature IQE improvement of the type-I and type-II c/s NWs and the appropriateness of the mid-infrared PL analyses for narrow-gap NW evaluation.

Taming non-radiative recombination in Si nanocrystals interlinked in a porous network

A range of the distinctive physical properties, comprising high surface-to-volume ratio, possibility to achieve mechanical and chemical stability after a tailored treatment, controlled quantum confinement and the room-temperature photoluminescence, combined with mass production capabilities offer porous silicon unmatched capabilities required for the development of electro-optical devices. Yet, the mechanism of the charge carrier dynamics remains poorly controlled and understood. In particular, non-radiative recombination, often the main process of the excited carrier's decay, has not been adequately comprehended to this day. Here we show, that the recombination mechanism critically depends on the composition of surface passivation. That is, hydrogen passivated material exhibits Shockley-Read-Hall type of decay, while for oxidised surfaces, it proceeds by two orders of magnitude faster and exclusively through the Auger process. Moreover, it is possible to control the source of recombination in the same sample by applying a cyclic sequence of hydrogenation-oxidation-hydrogenation processes, and, consequently switching on-demand between Shockley-Read-Hall and Auger recombinations. Remarkably, irregardless of the recombination mechanism, the rate constant scales inversely with the average volume of individual silicon nanocrystals contained in the material. Thus, the type of the non-radiative recombination is established by the composition of the passivation, while its rate depends on the degree of the charge carriers' quantum confinement.

Ultrafast Auger process in few-layer PtSe2

Enhanced many-body interactions due to strong Coulomb interactions and quantum confinement are one of the most prominent features of two-dimensional systems. The Auger process is a representative many-body interaction typically observed in two-dimensional semiconductors, determining important physical properties of materials, such as carrier lifetime, photoconductivity, and emission quantum yield. Recently, platinum dichalcogenides, represented by PtSe2 and PtS2, have attracted great attention due to their superior air stability, thickness-dependent semimetal-to-semiconductor transition, and exotic magnetic characteristics. However, the Auger process in platinum dichalcogenides has not been investigated to date. Here, we utilized ultrafast optical-pump terahertz-probe spectroscopy to explore carrier dynamics in few-layer semiconducting PtSe2. Most of the excited carriers are trapped by defects within ∼10 ps after excitation due to high defect density. We overcome this challenge by raising the excitation intensity to saturate trap sites with carriers, and observed a many-body process involving the carriers that survived the rapid trapping. This process is not band-to-band Auger recombination, but rather defect-assisted Auger recombination in which free carriers interact with trapped carriers at defects. Theoretical simulations show that this three-body Auger process can be approximated as bimolecular recombination at the rate of ∼3.3 × 10-3 cm2 s-1. This work provides insights into the interplay between ultrafast many-body processes and defects in two-dimensional semiconductors.