Ideal delta doping of carbon in GaAs

Abstract

Delta doped carbon acceptors in molecular-beam-epitaxy-grown GaAs were investigated on the atomic scale with scanning-tunneling microscopy in cross-sectional configuration. Monolayer-sharp spatial distributions were found at the intended positions of the delta layers in a wide range of dopant concentrations from 3×1012∕cm2 up to 1×1014∕cm2. The carbon concentrations were checked independently with secondary-ion-mass spectroscopy. All distributions had full widths at half maximum around 0.85nm and were symmetric up to the highest concentration investigated. These results point out that even at the elevated growth temperature of 590°C, and for very high dopant concentrations, neither segregation nor diffusion plays an important role in delta doping of GaAs with carbon acceptors. The observed small spreading of the dopant distribution is attributed to the generic surface roughness during growth.