Characterization of homoepitaxial germanium p-n junctions for photovoltaic and thermophotovoltaic applications

In the present work we report the results of characterization of epitaxial Ge/Ge layers using vapour phase epitaxy using either only isobutilgermane as a precursor or adding doses of AsH₃ as surfactant to obtain a better surface morphology. When iBuGe partial pressure was below 4times10^-6, the Ge layers showed good morphology and crystallographic quality with best results on samples grown on exactly oriented (001) Ge substrates. The use AsH₃ as surfactant permitted to increase the iBuGe partial pressure used in the growth without degrading the layer properties, even if TEM revealed the presence of an high defect density at the interface. It was concluded that the surfactant, even if reported as "non reactive" in literature, was actually incorporated at the layer interface. A p-n junction using Au as ohmic contacts showed a good rectifying behaviour and an open circuit voltage comparable to that reported in literature for diffused Ge cells.