Superior optical (λ ∼ 1550 nm) emission and detection characteristics of Ge microdisks grown on virtual Si_0.5Ge_0.5/Si substrates using molecular beam epitaxy

We report the optical characteristics of relatively large sized (∼7.0–8.0 μm) but low aspect ratio Ge microdisks grown on a virtual Si_0.5Ge_0.5 substrate using molecular beam epitaxy following the Stranski–Krastanov growth mechanism. Grown microdisks with very low aspect ratio Ge islands exhibit direct band gap (∼0.8 eV) photoluminescence emission sustainable up to room temperature, enabled by the confinement of carriers into the microdisks. p–i–n diodes with an intrinsic layer containing Ge microdisks have been fabricated to study their emission and photoresponse characteristics at an optical communication wavelength of ∼1550 nm. A strong electroluminescence at 1550 nm has been achieved at low temperatures in the device for a very low threshold current density of 2.56 μA cm⁻² due to the strong confinement of injected holes. The emission characteristics of the fabricated device with respect to the injected current density and temperature have been studied. Novel emission and optical modulation characteristics at 1550 nm of the fabricated p–i–n device containing Ge microdisks grown on a virtual SiGe substrate indicate its potential for Si CMOS compatible on-chip optical communications. (paper)