We investigate the magneto-optical properties of excitons bound to single stacking faults in highpurity GaAs. We find that the two-dimensional stacking fault potential binds an exciton composed of an electron and a heavy-hole, and confirm a vanishing in-plane hole g-factor, consistent with the atomic-scale symmetry of the system. The unprecedented homogeneity of the stacking-fault potential leads to ultra-narrow photoluminescence emission lines (with full-width at half maximum 80 µeV) and reveals a large magnetic non-reciprocity effect that originates from the magnetoStark effect for mobile excitons. These measurements unambiguously determine the direction and magnitude of the giant electric dipole moment ( e · 10 nm) of the stacking-fault exciton, making stacking faults a promising new platform to study interacting excitonic gases.Introduction. The stacking fault (SF), a planar, atomically thin defect, is one of the most common extended defects in zinc-blende, wurtzite, and diamond semiconductors. A fundamental understanding of the SF potential is important for determining how the defect affects semiconductor device performance [1, 2], engineering heterostructures based on crystal phase [3][4][5], and providing a new twodimensional (2D) platform for fundamental physics [6,7]. Here we report on excitons bound to large-area, single SFs in high-purity GaAs, a unique system where SFs are easily isolated with far-field optical techniques. The atomic smoothness of the potential and extreme perfection of the surrounding semiconductor result in ultra-high optical homogeneity ( 80 µeV). This enables optical resolution of the SF exciton fine-structure and thus direct measurement of the giant built-in dipole moment ( e · 10 nm) via the magnetoStark effect. These results indicate that the extremelyhomogeneous SF potential may be promising for studies of many-body excitonic physics, including coherent phenomena [8-10], spin currents [11], superfluidity [12], long-range order [13][14][15][16][17], and large optical nonlinearities [18][19][20].Stacking fault photoluminescence. Figure 1(a) shows a spectrally resolved confocal scan of SF structures in a GaAs epilayer, excited with an above band-gap laser (1.65 eV, 1.5 K) [21]. The image is colored red, green or blue according to three characteristic emission bands shown in Fig. 1e. The narrow-band PL at 1.493 and 1.496 eV originates from excitons, electron-hole pairs, bound to the 2D SF potential [22,23]. The sample consists of a 10 µm GaAs layer on 100 nm AlAs on a 5 nm/5 nm AlAs/GaAs (10×) superlattice grown directly on a semi-insulating (100) GaAs substrate. Stacking fault structures nucleate near the substrateepilayer interface during epitaxial growth [21].The physical origin of the potential can be understood from the atomic structure of the SF defect: the lattice-plane ordering in the [111] direction of zinc-blende is modified

We analyse an InAs/GaAs‐based electric field tunable single quantum dot diode with a thin tunnelling barrier between a buried n+‐back contact and a quantum dot layer. In voltage‐dependent photoluminescence measurements, we observe rich signatures from spatially direct and indirect transitions from the wetting layer and from a single quantum dot. By analysing the Stark effect, we show that the indirect transitions result from a recombination between confined holes in the wetting or quantum dot layer with electrons from the edge of the Fermi sea in the back contact. Using a 17 nm tunnel barrier which provides comparably weak tunnel coupling allowed us to observe clear signatures of direct and corresponding indirect lines for a series of neutral and positively charged quantum dot states.

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Abstract-Individual dislocations in an ultra-pure GaAs epilayer are investigated with spatially and spectrally resolved photoluminescence imaging at 5 K. We find that some dislocations act as strong non-radiative recombination centers, while others are efficient radiative recombination centers. We characterize luminescence bands in GaAs due to dislocations, stacking faults, and pairs of stacking faults. These results indicate that lowtemperature, spatially-resolved photoluminescence imaging can be a powerful tool for identifying luminescence bands of extended defects. This mapping could then be used to identify extended defects in other GaAs samples solely based on low-temperature photoluminescence spectra.

The external quantum efficiency (EQE) of a GaAs|AlGaAs double heterostructure, grown by molecular beam epitaxy, is measured as a function of temperature in the range of 350-100 K. Record EQEs of >80% at 300 K and >98% below 150 K are obtained. The temperature-dependent lifetime measurement that corroborates the EQE data is also reported, suggesting that interface recombination remains the dominant mechanism for nonradiative decay. These results offer promising prospects for using these structures in thermal photovoltaic, electroluminescent, and laser cooling device applications.