UC Berkeley

Since the beginning of the new millennium, the nano-materials community has witnessed an exponential increase in the amount of research dedicated to inorganic semiconductor nanowires for optoelectronics. The prospect of miniaturized optoelectronics is enticing principally because they can enable new applications and scientific discoveries that are unattainable with traditional macroscopic devices. This potential has inspired academics to create nanowire-based devices such as gas and chemical sensors, photodetectors, light-emitting diodes, solar cells, waveguides, nanoscopic lasers, plasmonic lasers, and nonlinear optical converters. To continue the success of this field, it is critical to explore nanowires with improved functionalities for photonic applications. This work presents new developments for the next generation of nanowire optoelectronic devices.

The unique boundary conditions of nanowires were explored to grow thermodynamically metastable materials directly onto bulk semiconductors. Using a single material, InGaN, single-crystalline nanowire light-emitting diodes that emit from blue to orange were fabricated without any evidence of phase separation, suggesting that the nanowire geometry relieves the significant lattice strain traditionally observed in macroscopic devices.

To circumvent the lack of spectral control in nanowire lasers, a coupled cavity scheme was introduced into nanowire lasers to improve the laser performance at room-temperature. By axially coupling two nanowire cavities, spectral manipulation of the lasing modes in semiconductor nanowires were theoretically investigated and experimentally demonstrated. This compact architecture produced single-mode lasing with the added benefit of lowering the laser threshold with respect to the individual component cavities.

Using these design principles for spectral manipulation, distributed Bragg reflectors (DBRs) integrated within semiconductor nanowires were explored to spatially and spectrally control specific longitudinal modes to demonstrate wavelength division, to improve laser performance, and to use as a platform to measure the effective refractive index of a waveguide made from a birefringent material. Using the results presented in this thesis, a discussion on the development of next-generation nanowire lasers is presented.