Very low energy electron microscopy of doped semiconductors

Very low energy electron microscopy in the range 1-5,000 eV has been used to image doped silicon regions in silicon. The contrast between the n-type and doped regions of n⁺ (As, 2.5X10²⁰ cm^-3) and p⁺ (B, 8X10¹⁹ cm^-3) appears at electron energies of ~3 keV. The n⁺ region is brightest followed by the p⁺ then the n-type substrate. The highest contrast between the different regions is achieved below 500 eV. Analysis by Auger spectroscopy revealed a surface layer of graphitic carbon. The contrast mechanism is explained in terms of metal-semiconductor contacts.