Halide Vapor Phase Epitaxy of Ge from an Elemental Source

Abstract

Halide vapor phase epitaxy shows promise for low-cost photovoltaic device manufacturing because of its high growth rates and lower cost elemental precursors but previously has not been used to deposit epitaxial Ge. Here, we demonstrate Ge deposition by generating GeCl₂ in situ from solid Ge and HCl in a N₂ ambient. To achieve Ge growth, we inject AsH₃ and PH₃ as sources of active hydrogen to the growth surface to create a driving force for growth. We do not observe Ge growth unless a supply of hydrogen is added, consistent with thermodynamic calculations. Furthermore, we show the hydrogen source must crack readily on the substrate surface to enable growth; relatively stable sources such as H₂ do not cause growth. Unintentional group V doping is one drawback of using AsH₃ and PH₃ to drive the Ge reaction. We observed As or P concentrations in the Ge films ranging from 4 × 10¹⁷ to 1 × 10¹⁸ atoms/cm³, concentrations that can drastically influence device characteristics. However, we note there are numerous other “helper molecule” options that can provide active hydrogen without doping or etching the material. This work provides a path forward for Ge deposition for optoelectronic devices from an elemental source.

In this work we were able to deposit Ge from an elemental source for the first time on a Halide Vapor Phase Epitaxy reactor. We achieve growth by injecting a source of hydride like arsine to create a driving force for growth. We showed computational and experimental data that support the growth results and, also the high crystalline quality achieved.