A COMPARISON OF ELECTRICAL AND CHEMICAL PROFILING OF DOPING SUPERLATTICES IN SILICON

Molecular-beam epitaxy was used to grow vertical silicon structures with extremely sharp doping transitions. Hereby a series of modulation-doped multilayer structures was prepared which had successively reduced period lengths from 100 down to 4 nm. These test samples are appropriate to study the depth resolution of standard electrical and chemical profiling techniques. Secondary ion mass spectrometry is able to resolve doping modulations down to 4 nm. Electrical measurement techniques are fundamentally limited by the out-diffusion of carriers from the highly to the lowly doped layers. Such effects become of increased importance in small period superlattices. Spreading resistance is only able to resolve the doping modulations of the test sample with the largest period length (100 nm).