III-Nitride Optoelectronics

The semiconductor system InN-GaN-AlN spans a vast energy range of direct band gaps, however since the lattice constant varies over a large range across the different InGaN-AlGaN compositions, it is not typically possible to combine large differences in bandgap in a single epitaxial heterostructure without causing the layers to crack or form huge defect concentrations. This is overcome utilizing nanowire heterostructures. Using plasma-assisted molecular beam epitaxy (PA-MBE) we grow self-catalyzed III-Nitride nanowires on a variety of substrates: including integration with Si and even flexible metallic substrates. Not only does bandgap vary strongly, but also polarization, enabling the combined toolset of band gap and polarization engineering within III-Nitride nanowire heterostructures. Our exploration into the design space opened by this optoelectronic material platform has led to the demonstration of many new device geometries and optoelectronic properties including:

  • Dopant-less diodes: pn-diodes formed without donor or acceptor doping by polarization grading alone
  • Negative differential photocurrent: non-linear responsibity due to optically controlled internal electric fields
  • Nanowire LEDs grown directly on flexible metal substrates
  • Coaxial double barrier resonant tunneling nanowires
  • Tunnel-junction nanowire LEDs
  • Tunable free hole concentrations in nanowires
  • Deep ultraviolet emitting nanowire LEDs

Over the last 10 years we have amassed a large library containing a variety of these unique III-Nitride nanowire heterostructures. Such materials are provided to collaborators around the world.