The influence of the mesa size on the structural and luminescence propertie
s of Ge island layers deposited by low-pressure chemical vapour deposition
was studied. Diode structures containing one Ge island layer were grown sel
ectively on patterned wafers with variable area. The analysis shows that th
e electroluminescence spectra could be separated into three contributions l
ying at low-, medium and high-energy positions, respectively. The absolute
peak intensity of each signal depends on the mesa size and on the injected
current density. The signal at the low-energy position was assigned to an e
ffect due to the facets of the diodes; the two other signals originate from
islands on the (001) plane having different Si contents or strain states o
n the (001) plane.