Impurity-doped p(+) and n(+)-GaAs epitaxial thin layers were grown on (001) GaAs substrates by molecular layer epitaxy (MLE) using an intermittent supply of AsH3 and TEG in an ultra high vacuum. The surface stoichiometry before the introduction of the impurity precursor was controlled by changing the gas supply sequences and supply time. It was shown that the incorporation of Be is extremely enhanced when the layer is exposed to Be(MeCp)(2) after TEG supply. When DETe was supplied to a GaAs surface covered with S, the incorporation of Te was enhanced and it was shown that the concentration of Te increased with increasing S coverage. Be doping and alternate Te and S doping were also applied for the fabrication of ultrashallow sidewall tunnel junctions. As a result, these tunnel junctions have shown record peak current densities of up to 31,000 A/cm(2) at RT. (C) 2004 Elsevier B.V. All rights reserved.