Effect of Anisotropic Strain on the Crosshatch Electrical Activity in Relaxed GeSi Films

Abstract

The physical origin of the crosshatch electrical activity in relaxed GeSi films was studied using a near-field scanning optical microscope (NSOM). The contrast and patterns in the near-field photocurrent images depend on the polarization direction of the NSOM light. These results rule out composition nonuniformity, junction depth variation, and scanning artifacts as dominant sources of the contrast. Numerical calculations show that local changes in band structure due to strain fields of the misfit dislocations are responsible for the experimental observations.

Direct Photocurrent Mapping of Organic Solar Cells Using a Near-Field Scanning Optical Microscope

“…Using the light from an NSOM fiber and scanning it across the device, we show that it is possible to observe the effect of phase segregation and inhomogeneous blending on charge generation and collection directly, without having to infer it from other techniques. Although NSOM has been applied previously for photocurrent mapping studies (for example, to study GeSi dislocations , and the photoconductivity of stretch-oriented PPV planar gap devices), we believe that this study is the first application of the technique to probe organic solar cells in situ directly. The use of the NSOM technique directly on a fully fabricated device is achieved by illuminating through a semitransparent metal electrode that is only 30 nm thick.…”

Optical nanoscopy of transient states in condensed matter

“…3a,b ) with the different stripes having the same SiGe concentration, but experiencing a non-uniform mechanical stress that leads to unequal local optical properties. Moreover, the stress-induced optical response 37 , varies appreciably due to band shifting of up to 0.1 eV/GPa for pure silicon and 0.15 eV/GPa for pure germanium. Hence, in particular when pumping with wavelengths matching the band gap of 1.07 eV, the stripes’ absorptions differ dramatically.…”

Mapping Sub‐Surface Structure of Thin Films in Three Dimensions with an Optical Near‐Field

“…In all fields of knowledge, the ability to see through and beyond surfaces is intimately connected with deeper understanding of phenomena. Within natural sciences, sub‐surface imaging is crucial to the study of a large variety of “natural” nanostructures (from sub‐cellular elements in living organisms to mixed phases and defects in a variety of materials) as well as of artificial, man‐made systems, that can be generated via either lithographic methods or via entropy‐driven phase‐separation processes, including the growth of quantum dots for single‐photon sources, or in the study of defects in electronic devices . Successful implementation of nanotechnology requires a variety of high‐resolution microscopy techniques, for both surfaces and the bulk, and this demand has been met with remarkable advances in far‐field nanoscale resolution optical microscopy, some of which were rewarded with the 2014 Nobel prize in chemistry.…”