Towards quantification of doping in gallium arsenide nanostructures by low-energy scanning electron microscopy and conductive atomic force microscopy

We calculate a universal shift in work function of 59.4 meV per decade of dopant concentration change that applies to all doped semiconductors and from this use Monte Carlo simulations to simulate the resulting change in secondary electron yield for doped GaAs. We then compare experimental images of doped GaAs layers from scanning electron microscopy and conductive atomic force microscopy. Kelvin probe force microscopy allows to directly measure and map local work function changes, but values measured are often smaller, typically only around half, of what theory predicts for perfectly clean surfaces.

LAY DESCRIPTION:

Doping means the intentional contamination of a semiconductor by foreign atoms that are integrated as ions into the crystal lattice after either donating (as donors) additional electrons or (as acceptors) electronic holes and thereby change the local electric properties. The resulting material is called n- or p-doped, and pn-junctions are used in all diodes and transistors that form the basic units of more complicated electronic devices such as computers or solar cells.

We calculate how doping changes the energy needed to extract an electron from the semiconductor (called its work function) and how this influences the secondary electron yield in scanning electron microscopy and resistive or Kelvin probe measurements in conductive atomic force microscopy. Both microscopy methods can be used to directly map the spatial distribution of dopants in doped nanostructures but quantitative measurements are difficult due to the influence of surface effects.