High spatial resolution studies of microscopic capacitors in GaAs

Cross-sectional scanning tunneling microscopy (XSTM) studies of microscopic capacitors fabricated in GaAs using Be and Si delta-doped layers, have been successfully completed at TASC. Major issues addressed include impurity redistribution in the growth direction across adjacent delta-doped layer, the minimum distance at which a stable electrostatic dipole could be fabricated, and the feasibility of determining the electrostatic potential distribution in nanostructures by XSTM. To this purpose, a number of samples were fabricated by molecular beam epitaxy (MBE), which included alternate Si donor and Be acceptor delta-doped layers with variable spacing. The samples were cleaved in ultra-high- vacuum (UHV) in order to expose {110} cross-sections of the epilayers with negligible step and defect density within the sampled areas. Transmission electron microscopy (TEM) experiments on cross-sectioned {110}-specimens produces further information on the bulk structural properties of ?-doped layers. Moreover, high spatial resolution details on the distribution of the chemical species and on the electronic structure of the interfaces could be achieved by using a field emission gun (FEG) as an electron source.