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.

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Epitaxial layers of GaAs on (100) GaAs substrates can be grown by close-spaced vapor transport using water vapor as the transporting agent. The parameters for the transport are Ti = 755°C. AT' = 45°C. and 6 = 0.03 cm (where Ti is the temperature of the graphite heating the substrate; AT', the temperature difference between the graphite heating the source and the one heating the substrate; and 6. the thickness of the spacer separating the GaAs source and the substrate). Mirrorlike epitaxial layers of GaAs are obtained with these parameters when water vapor, at a partial pressure of 4.58 Torr ( 1 Torr = 133.3 Pa), is introduced with H, at the beginning of the temperature rise of the reactor. The dimensions of the epitaxial layer are only limited by the size of the reactor. Using the same growth conditions. it is not possible to obtain mirrorlike films of GaAs on (100) Ge substrates. Instead, the layers are dull grey (sample no. I ) . It is howcder not a polycrystalline deposition since the pole figures, obtained by X-ray diffraction. reveal only four crystallographic orientations: {loo} the main one. {221} the secondary one, and {021} + {I 12) two minor contributions. Mirrorlike films of GaAs on (100) Ge substrates of less than 1 cni' have been obtained with T: = 775OC. AT' = 25°C. and 6 = 0.03 cm. With these conditions, the growth rate is 0.25 + 0.08 k m m i n I . The time evolution of T: and AT', froni room temperature up to the equilibrium temperature also influences the surface morphology of GaAs films on Ge while this was not the case for GaAs films on GaAs substrates. When the Ge substrate is larger than I cm'. the centre of the film becomes textured but the edges reniain mirrorlike (sample no. 2). Pole figures obtained for the center and the edges of sample no. 2 are similar. They are characterized by one large diffraction due to the (100) orientation. A few random crystallographic orientations and sometimes the {221} orientation, however, bearly emerge froni the background of these pole figures. Also transmission electron microscopy does not reveal any major difference between the center and the edges of sample no. 2. The density of threading dislocations is the sanie for both regions, varying from 10' c m ', close (2-3 k m ) to the interface, to lo7 c m ' in the thickness of the film. No misfit dislocations were observed.Antiphase boundaries are present in both regions as well. The only difference between the centre and the edges of sample no. 2 involves microtwin bundles: in the center region, there are two microtwin bundles per micrometre of interface, extending up to 6 km in the GaAs film while on the edges, there is one bundle per micrometre with an extension of only one micrometre into the epitaxial layer. Mirrorlike GaAs films can be obtained on (100) Ge substrates of at least 1 in ( 1 in = 2.5 cni) in diameter by increasing 6 to 0.2 cm and by injecting water vapor in the reactor only when Ti reached 650°C: the other deposition parameters reniain the sanie as for sample no. 2. In these conditions, th...

normalGaAs epitaxial films have been deposited on heavily Si‐doped (100) normalGaAs substrates by closely spaced vapor transport from a semi‐insulating (undoped) normalGaAs source. Charge density (N) profiles of the epitaxies have been determined electrochemically by a succession of photocorrosion steps and capacitance measurements. When the films are thick enough, typicalN profiles show four regions. Starting from the surface of the film and going toward the normalGaAs substrate, there is a first region (I) of constant N, extending over a length varying with the deposition time. It is followed by a second region (II) extending over 12±2 μnormalm , where N slowly rises. In region III , there is an abrupt increase of N followed by region IV which is the substrate region. Consistently, close spaced vapor transport technique layers were n‐type with N values in region I varying from 4×1015 normalto 2×1016 cm−3 . Region III of the N profile displays a fine structure which has been explained in terms of Si which is released from the Si‐doped normalGaAs substrate into the vapor phase and redeposited within the growing film. Region III is also due to Si diffusion from the substrate into the growing film. A diffusion coefficient of Si into normalGaAs of 6.5±2.5×10−14 cm2 s−1 at 760°±3°C has been calculated from the N profile curves. The slow variation of N in region II results neither from a fast diffusive shallow donor impurity from the normalGaAs substrate, nor from Si released from region III into the vapor phase and redeposited into the growing film. It is suggested that region II probably reflects a variation of the off‐stoichiometry in the epitaxial film. Epitaxial layers of normalGaAs grown on semi‐insulating (SI) (100) normalGaAs substrates show region I and II of the N profile curve. Hall effect measurements performed on these layers agree with the electrochemical results.