Zeitschriftenaufsätze

For vertical-cavity surface-emitting lasers (VCSELs) or photoelectrochemical devices and high efficient III-V/Ge(100) photovoltaics, preparation of double-atomic steps on Ge(100) substrates is highly recommended in order to avoid anti-phase boundaries in the III-V buffer layers. These Ge(100) surfaces were investigated in detail under As- and GaAs-rich MOVPE reactor conditions. During initial growth of III-P buffer layers, however, on an atomically well-ordered Ge(100):As surface, As-P exchange takes place, during which double-layer steps should be preserved. Here, we apply in situ monitoring to study the interaction of P with vicinal Ge(100):As surfaces under realistic, GaAs-rich CVD reactor conditions at growth temperature. In situ optical spectroscopy in combination with surface science techniques in ultra-high vacuum ambience is used to investigate the Ge(100) surface. We show that different Ge(100):As/P heterointerfaces are formed depending on the applied molar flow of phosphorus precursors. Despite the lattice-matched quality of the probing III-P layer, this critical heterointerface impacts significantly the surface roughness and the formation of crystal defects in the subsequently grown III-P buffer layers.

We investigate the spontaneous emission noise resilience of the phase-locked operation of two delay-coupled nanolasers. The system is modeled by semi-classical Maxwell-Bloch rate equations with stochastic Langevin-type noise sources. Our results reveal that a polarization dephasing time of two to three times the cavity photon lifetime maximizes the system’s ability to remain phase-locked in the presence of noise-induced perturbations. The Langevin noise term is caused by spontaneous emission processes which change both the intensity auto-correlation properties of the solitary lasers and the coupled system. In an experimental setup, these quantities are measurable and can be directly compared to our numerical data. The strong parameter dependence of the noise tolerance that we find may show possible routes for the design of robust on-chip integrated networks of nanolasers.

Oxygen vacancies (OVs) have been reported to significantly alter the photocatalytic properties of BiOCl nanosheets. However, their formation mechanism and their role in the enhancement of photoelectrochemical performance remain unclear. In this work, thermally induced oxygen vacancies are introduced in BiOCl nanosheets by annealing in He atmosphere at various temperatures and their formation mechanism is investigated by in-situ diffuse reflectance infrared (DRIFTS) measurements. The influence of OVs on band offset, carrier concentrations and photoelectrochemical performance are systematically studied. The results show that (1) the surface of BiOCl nanosheets is extremely sensitive to temperature and defects are formed at temperatures as low as 200 ˚C in inert atmosphere. (2) The formation of surface and bulk OVs in BiOCl is identified by a combination of XPS, in-situ DRIFTS, and EPR experiments. (3) The photocurrent of BiOCl is limited by the concentration of charge carriers and shallow defect states induced by bulk oxygen vacancies, while the modulation of these parameters can effectively increase light absorption and carrier concentration leading to an enhancement of photoelectrochemical performance of BiOCl.

Nanosponges are subject of intensive research due to their unique morphology, which leads among other effects to electrodynamic field localization generating a strongly nonlinear optical response at hot spots and thus enable a variety of applications. Accurate predictions of physical properties require detailed knowledge of the sponges’ chaotic nanometer-sized structure, posing a metrological challenge. A major goal is to obtain computer models with equivalent structural and optical properties. Here, to understand the sponges’ morphology, we present a procedure for their accurate 3D reconstruction using focused ion beam tomography. Additionally, we introduce a simulation method to create nanoporous sponge models with adjustable geometric properties. It is shown that if certain morphological parameters are similar for computer-generated and experimental sponges, their optical response, including magnitudes and hot spot locations, are also similar. Finally, we analyze the anisotropy of experimental sponges and present an easy-to-use method to reproduce arbitrary anisotropies in computer-generated sponges.