Cathodoluminescence Characterization of Semiconductor Doping at the Nanoscale

Semiconductor nanostructures open new perspectives for light trapping, lattice-mismatched crystal growth (III-V on Si for instance) and novel transport phenomenon for next generation photovoltaics. The characterization of material properties at the nanoscale remains challenging. In particular, doping is a key parameter in the design and fabrication of solar cells. Here, we show that cathodoluminescence mapping can be used to determine both n-type and p-type doping levels of GaAs with nanometer resolution. n-type semiconductor shows characteristic blueshift emission from the electron filling, while ptype semiconductor exhibits redshift emission due to dominant bandgap narrowing at high concentrations. The generalized Planck's law is used to fit the whole spectra and extract electron Fermi levels (n-type) and effective bandgap (p-type). Quantitative doping assessment is achieved by systematic spectral analysis, and is demonstrated on planar GaAs layers, and on single GaAs nanowires. This method can be extended to other semiconductors and nanostructures.