The bright emission from thick flakes makes gallium selenide a fantastic material for understanding the relationship between local strain and optical response. Here, we investigate complex strain distributions by transferring gallium selenide flakes onto nanostructures patterned in close proximity, enabling the study of a variety of strain distributions, such as uniaxial, biaxial, and triaxial strain within a single flake. Our findings reveal that finite strain distributions and resulting bandgap shifts occur in regions of gallium selenide suspended between closely-spaced nanostructures, in good agreement with strain distributions simulated using finite element analysis. This research paves the way for designer strain distributions and tailorable nanophotonic behavior in two-dimensional materials.
Strain engineering of the two-dimensional semiconductor gallium selenide has recently revealed exciting nanophotonic effects such as localized bandgap tuning, exciton funneling, and the creation of site-specific single photon emitters. We investigate the reversible local strain engineering of suspended gallium selenide flakes by using a novel micromechanical spring with nanoscale probes for inducing symmetry-controlled localized strain. By performing strain engineering measurements on suspended gallium selenide flakes as opposed to using patterned substrates, unintended strain originating from the surrounding environment is avoided. Our results show that gallium selenide undergoes a reversible bandgap redshift of >6 meV. The presented research establishes a new platform for streamlining the quantitative understanding of material properties as a function of complex local strain in two-dimensional materials for quantum photonics applications.
Three-dimensional (3D) topological insulators (TI) with large spin Hall conductivity have emerged as potential candidates for spintronic applications. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet Fe78Ga13B9 (FeGaB) and 3D TI Bi85Sb15 (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. The spin pumping parameters derived from inverse spin Hall effect (ISHE) measurements are consistent with the results of femtosecond light-pulse induced THz emission. These measurements are successfully verified using theoretical calculations of thickness-dependent spin Hall conductivity of BiSb thin films based on a tight-binding model.
P-type doping of wide-band-gap oxides such as In2O3 and Ga2O3 would open vast opportunities in device in device design, ranging from transparent contacts for solar cells to high-power transistors. In this presentation we discuss the fundamental difficulties concerning p-type doping in these materials and opportunities offered by forming dilute alloys, with minimum disturbance in structural parameters yet bringing beneficial changes to their electronic structure.
Using hybrid density functional theory, we investigate the influence on electronic structure of common defects and impurities in tungsten oxide (WO3). As an easily reducible perovskite with the A-site atom missing, high concentrations of foreign dopants and oxygen deficiencies are possible. Our calculations show that both oxygen vacancies and alkali dopants are shallow donors, and we explore the physical origins for this behavior. In particular, we examine whether oxygen vacancies can give rise to localized states or small polarons. Our results show that in crystalline material no such charge localization occurs. We discuss how these results impact electrical conductivity and optical properties.
Optical spectroscopy is a powerful approach for detecting defects and impurities in ZnO, an important electronic material. However, knowledge of how common optical signals are linked with defects and impurities is still limited. The Cu-related green luminescence is among the best understood luminescence signals, but theoretical descriptions of Cu-related optical processes have not agreed with experiment. Regarding native defects, assigning observed lines to specific defects has proven very difficult. Using first-principles calculations, we calculate the properties of native defects and impurities in ZnO and their associated optical signals. Oxygen vacancies are predicted to give luminescence peaks lower than 1 eV; while related zinc dangling bonds can lead to luminescence near 2.4 eV. Zinc vacancies lead to luminescence peaks below 2 eV, as do the related oxygen dangling bonds. However, when complexed with hydrogen impurities, zinc vacancies can cause higher-energy transitions, up to 2.3 eV. We also find that the Cu-related green luminescence is related to a (+/0) deep donor transition level.
Titanium dioxide is a versatile material with ubiquitous applications, many of which are critically linked to either light absorption or transparency in the visible spectral range in addition to electrical conductivity. Doping is a well-known way to influence those properties in order to bring them into a desired range. Working towards a comprehensive understanding of the electronic and optical properties of TiO2 (as well as of the link between them) we review and summarize electronicstructure results that we obtained using cutting-edge theoretical spectroscopy techniques. We focus on the formation of electron and hole polarons and we elucidate the influence of doping on the optical properties of TiO2. In addition, we present new results for the reflectivity of pure TiO2.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.