GaAs epitaxial layers obtained by close-spaced vapor transport in H2 + H2O and H2 + CO2 ambients: Fine control of the growth rate and its effect on the electrical properties of the layers

Abstract

In view of developing the close-spaced vapor transport technique (CSVT) to obtain III/V homojunction solar cells, it is necessary to finely control the growth rate of GaAs epitaxial layers. This has been performed either by controlling the water vapor pressure, [Formula: see text] injected in the reactor along with H2, in H2 + H2O ambient, or by controlling the water vapor pressure generated in situ by the reaction of H2 + CO2 in the reactor. For H2 + CO2 ambient, [Formula: see text], controls [Formula: see text] according to the following reaction: [Formula: see text]. The growth rates calculated with a diffusion controlled model are in agreement with the experimental values for both ambients, including the observation of a maximum in the evolution of the growth rate with [Formula: see text], Controlling the growth rate of GaAs by changing [Formula: see text] affects the carrier density (NA–ND) of p-type layers grown from Zn-doped GaAs sources. In both ambients (NA–ND) is a function of [Formula: see text]. Such a behavior is also obtained for the calculated carrier densities. It is the result of the transport of Zn as ZnO in CSVT. In H2 + CO2 ambient, where H2O and C are generated in situ, carbon is not incorporated as a major p-type doping impurity, contrarily to expectations, n-type GaAs layers were also obtained from Te-doped GaAs sources. In that case, the measured NA–ND values are not affected by changes in [Formula: see text] because water is not involved in the transport of Te in CSVT.