We present a magneto-optical study of the carrier dynamics in compressively strained Ge 1−x Sn x films with Sn content up to 10% epitaxially grown on Ge on Si(001) virtual substrates. We leverage the Hanle effect under steady-state excitation to study the spin-dependent optical transitions in the presence of an external magnetic field. This allows us to obtain direct access to the dynamics of the optically induced carrier population. Our approach reveals that at cryogenic temperatures the effective lifetime of the photogenerated carriers in coherent Ge 1−x Sn x is on the subnanosecond timescale. Supported by a model estimate of the radiative lifetime, our measurements indicate that carrier recombination is dominated by nonradiative processes. Our results thus provide central information to improve the fundamental understanding of carrier kinetics in this advanced direct-band-gap group-IV-material system. Such knowledge can be a stepping stone in the quest for the implementation of Ge 1−x Sn x -based functional devices.
The Rashba effect in Ge/Si0.15Ge0.85 multiple quantum wells embedded in a p‐i‐n diode is studied through polarization and time‐resolved photoluminescence. In addition to a sizeable redshift arising from the quantum‐confined Stark effect, a threefold enhancement of the circular polarization degree of the direct transition is obtained by increasing the pump power over a 2 kW cm−2 range. This marked variation reflects an efficient modulation of the spin population and is further supported by dedicated investigations of the indirect gap transition. This study demonstrates a viable strategy to engineer the spin‐orbit Hamiltonian through contactless optical excitation and opens the way toward the electro‐optical manipulation of spins in quantum devices based on group‐IV heterostructures.
Nowadays, due to the advances in nanolithography technology it is possible to fabricate structures whose electronic properties correspond to that of a quasi-one-dimensional electron gas. Such structures allow us to observe ballistic quantum transport at low temperatures, and remarkable experimental observations have resulted1. Many theoretical studies have investigated conductance fluctuations2 and voltage controlled defects. Cahay et al3 studied the problem of localization associated with the conductance fluctuations of an array of elastic scatterers. Joe et al4 discussed the effects of a voltage controlled impurity for the conductance of a single open quantum box. As the impurity size is changed, it causes conductance oscillations due to the interference of circulating and bound states of the quantum box. In this paper we analyze how changes in geometry of a structure with three open dots affect its electronic properties.
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