Very abrupt doping structures grown by Si molecular beam epitaxy are investigated by spreading resistance (SR) analysis. The corresponding SR profiles reveal strong carrier spilling effects. To calculate the ‘‘on bevel’’ carrier concentrations of these structures, a formalism is developed which is based on the Poisson–Boltzmann equation. Qualitative agreement between the model calculation and the SR data is established.
A quantitative comparison is made of the junction depths determined by spreading resistance (SR) and secondary-ion mass spectrometry (SIMS) for submicron abrupt pn junctions (grown by molecular beam epitaxy) and Gaussian implants. The discrepancies between SR and SIMS are explained in terms of carrier spilling. From the comparison with a theoretical model, general trends can be adequately explained. In order to overcome the uncertainties imposed by the boundary conditions in this model, experimental diagrams are derived which can be used in routine analysis to assess the importance of carrier spilling effects in SR.
Interfacial p doping due to B contamination is routinely detected in Si molecular-beam epitaxy (MBE) when using standard MBE cleaning schemes. The influence of the wet chemical precleaning as well as of the in situ cleaning is investigated with respect to this effect: whenever chemical precleaning results in a hydrophilic Si surface, interfacial p-type doping due to B contamination of 1012 cm−2 is detected, whereas for hydrophobic Si surfaces the B contamination is reduced by a factor of about 50. Concerning the in situ cleaning, a reduction of the preheating temperature TH correlates with a decrease of p-type doping for hydrophilic cleaned samples, though the chemical B contamination is independent of TH, i.e., the in situ preheating induces an electrical activation of the B contamination.
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