OSE Seminars
Defects in semiconductors: atomic-like systems in a solid-state host
Presented by Kai-Mei Fu, University of Washington Physics and Electrical Engineering Departments
Defects provide potentials for quantum particles (electrons and holes) in crystals. In high purity crystals, the quantum-confined particles can behave similarly to atoms, enabling atomic-like physics in the solid state. In this seminar, I present results on two fundamental defects ubiquitous in semiconductors, the stacking fault and the substitutional donor. In both experiments, the high-purity of the semiconductor results in exceptionally sharp excitonic optical transitions that can be utilized to determine the fundamental properties of the defect-bound carriers.
In the first experiment, we show that stacking faults (SF) provide the most homogeneous 2D potential for excitons yet reported1. The narrow transitions enable us to observe a magnetic non-reciprocity effect in which the energy of the excitonic emission depends on the sign of the magnetic field. This effect, due to conservation of the exciton two-dimensional momentum, provides evidence that excitons are mobile in this novel potential and enables a measurement of the giant SF exciton dipole moment (~10 nm). The large dipole moment combined with the high optical homogeneity demonstrates potential for stacking faults as a novel platform to study coherent phenomena in interacting excitonic gases.
If time permits, I will present recent results on spin lifetimes for electrons bound to substitutional donors. We measure the longitudinal relaxation (T1) in three semiconductors, GaAs, InP, and CdTe. Unexpectedly, the maximum observed T1 is similar in all materials (~ 1 ms) and the relaxation time is inversely proportional to B3. I will discuss the surprising implications of this result in terms of known spin-relaxation mechanisms in direct band gap semiconductors.
1T. Karin et al., "Fundamental properties of 2D excitons bound to single stacking faults in GaAs," arxiv.org/abs/1601.03991 (2016)
10:00 am, Friday, February 19, 2016
Room 101, Center for High Tech Materials
Science and Technology Park - South Campus
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