Using H2O as a transport agent, epitaxial GaAs layers were grown by the close-spaeed vapor transport technique (CSVT) on (100) heavily Si-doped GaAs substrates. Three kinds of GaAs sources were used for the deposition: (100) GaAs, heavily doped with Te or Si, and undoped semi-insulating (SI) (100) GaAs. The growth rates obtained with SI and Te-doped GaAs are quite similar and show a clear tendency to be superior to the growth rates measured for Si-doped GaAs sources. Uncompensated charge carrier density (ND – NA) profiles have been measured electrochemically for the layers grown with the three kinds of sources. When Te-doped GaAs is used, (ND – NA) obtained for the epitaxy is the same as that of the source, implying a complete transfer of the Te impurity. (ND – NA) values varying from 1016 to 1018 cm−3 are obtained from SI GaAs sources, depending upon the thickness of the epitaxial layer. (ND – NA) < 1015 cm−3 are measured for layers grown from Si-doped GaAs sources. In this case, layers thicker than 10 μm cannot be mesured electrochemically because of their excessively high resistance. The small (ND – NA) values obtained in that case are explained by the reaction of Si contained in the source with the transport agent (H2O), resulting in the formation, at the Si-doped GaAs surface, of a passivating SiOx layer revealed by Auger spectroscopy. This passivating layer also explains the smaller growth rates measured with these sources. p–n Junctions have been prepared by Zn diffusion in CSVT layers grown from SI GaAs sources. Their I–V characteristics show good rectification behavior, indicating that the CSVT layers could be used for photovoltaic purposes.
Chemical Vapor Transport Reactions - Arguments for Choosing a Suitable Transport Agent
