Materials Engineering for Optoelectronic Device Applications

schematic of materials Tyler Grassman Research Lab Ohio State

While a number of optoelectronic devices may utilize a lattice-matched, homovalent semiconductor system (III-V on III-V, for instance), the need for improved performance and functionality at both the materials and device-level requires the integration of lattice-mismatched and/or heterovalent (III-V on Si, for example) semiconductor materials. However, the growth of such lattice-mismatched, heterovalent materials may lead to the introduction of both extended defects (such as dislocations, stacking faults, and micro twins) and point defects (interstitials, substitutional impurities, etc.). In many cases, such defects can govern or limit the electronic behavior of semiconductor devices. As such, our group's research often aims to better understand, mitigate/eliminate, or engineer around these defects.

Our major research thrusts to this end include the development of growth processes via molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD, also known as MOVPE) for lattice-mismatched and heterovalent epitaxy, demonstration of prototype photodetector and photovoltaic device technologies, and characterization of material and device quality.

Development of III-V/Si heteroepitaxy via MBE and MOCVD

GaP/Si development for high-quality monolithic integration of GaAsP on Si for photovoltaic applications
Investigation of the III-V/IV heterovalent interface with (B)GaP/Si grown by molecular beam epitaxy (MBE)
Computational dislocation modeling to understand dislocation dynamics in GaP/Si
Strain engineering to mitigate excessive dislocation formation in lattice-mismatched epitaxial systems
Demonstration of prototype photodetector and photovoltaic device technologies
- GaAsP/Si tandem solar cells grown via metal-organic chemical vapor deposition (MOCVD)
  - Terrestrial solar cells (world record efficiencies)
  - Space solar cells
- IR photodetectors
- High-performance metamorphic III-V tunnel junctions
- Textured polydimethylsiloxane (PDMS) sheets for path length enhancement
Characterization of material and device quality via scanning electron microscopy (SEM), transmission electron microscopy (TEM), quantum efficiency (QE), light current-voltage (LIV), photoluminescence (PL), etc.

Development and Application of Advanced Electron Microscopy Methods

disc and microchips, Tyler Grassman research at Ohio State

Beyond the characterization of various semiconductor materials for optoelectronic devices, our group has worked to apply and develop various electron microscopy methods. These include quantitative defect characterization via electron channeling contrast imaging (ECCI) performed in a scanning electron microscope (SEM), high-resolution functional characterization with electron energy loss spectroscopy (EELS) performed in a scanning transmission electron microscopy (STEM), a suite of correlative microscopy and spectroscopy methodologies, and more.