UC Santa Cruz

Research of heteroepitaxial growth and deposition of semiconductor and metallic nano-materials is significant in materials science and engineering for numerous applications due to the significant flexibilities in designing distinctive material systems it offers.

Semiconductor nanowires on mechanically flexible metallic substrates by heteroepitaxial growth, as a novel material platform, could be very promising for many applications. The epitaxial growth of semiconductor (indium phosphide and silicon) nanowires by metal organic chemical vapor deposition and plasma enhanced chemical vapor deposition are developed with the goal of understanding their electrical, thermal and optoelectronic properties while developing scalable, manufacturable solutions for thermoelectric devices at a low cost. However, it is extremely difficult to grow semiconductor nanowires directly on the metallic substrates mainly because of the reaction between the growth precursors and the substrates. Aluminum-doped zinc oxide thin film on polycrystalline copper foil was proposed and demonstrated for indium phosphide nanowire growth, as well as establishing a reliable electrical contact by utilizing conductive oxide thin films as a template layer. A thin film of titanium nitride barrier layer was utilized to assist silicon nanowire growth on copper foils by forming an Ohmic contact between the nanowires and the substrates.

On the other hand, heteroepitaxy of metallic thin films on semiconductor substrates was extensively studied as a method of electrode plating for various devices. Significant drawbacks still existed in this relatively matured material system, e.g. the rough surface of ultra thin silver film on silicon substrates as a significant obstacle for optoelectronics devices. A thin germanium nucleation layer was introduced to adjust the surface roughness of the silver thin films. This demonstration of ultrasmooth silver thin films offers an advantageous material platform with scalability for applications such as optics, plasmonics, and photonics.