RET Projects

RET Experience: Semiconductor Characterization

Projects

Topography of Semiconductor Sensors: SAM on GaN

Self-Assembled Monolayers (SAM) on Gallium Nitride. SAMs are extremely thin layers, as small as one molecule thick. When in contact with a target substance, SAMs change the resistance and/or other properties of the attached semiconductor, signaling the target substance's presence. Topography scans and roughness calculations indicate successful growth conditions.

The AlGaN/GaN heterostructure has shown great potentail as a multifunctional biosensor due to its chemical stability, electrosensitivity in aqueous solution and its optical transparency. (Steinhoff et al. Advanced Functional Materials. 2003, 13, 841.)

Topography of AlGaN and GaN: Growth Conditions

AlGaN grown by MBE (Molecular Beam Epitaxy). The topography of these growths is very important. Because GaN and AlGaNare commonly grown on substrates that are different than their own (i.e. sapphire, SiC and Si), mismatches occur between the two types of crystal lattice. This generates defects, some of which result in the degradation of the performance of semiconductor devices. Growth conditions must be optimized to increase the repeatability of quality lattice structures.

TEM image showing dislocations due to lattice mismatching.

Model-Building

Construction of models is a helpful tool for understanding the structure and growth of crystal lattices. They allow us to study a visible representation of structures we would otherwise not be able to easily manipulate and observe.

AlGaN/GaN Wurtzite structure. Nitrogen: blue, Gallium: yellow, Alluminum: red. White outline around one unit cell.

GaAs Zinc-Blende structure. Gallium: gray, Arsenic: red. White ouline around one unit cell.