Electroreflectance Study of Light-Emitting Porous Silicon

ABSTRACTElectroreflectance spectroscopy measurements have been performed on light-emitting porous Si (LEPSi). The transmission electron microscope measurements reveal that LEPSi includes Si nanocrystals with a mean crystal size of 1–2 nm. The ER features are observed at a transition energy of 3.4 eV in all of the samples, giving that LEPSi still keeps the threedimensional (3D) electronic structure. Changes in the transition energies are not found for LEPSi with the different mean crystal sizes. Furthermore, we directly observed interband transitions of quantized states due to quantum-confined electron-hole (e-h) pairs in LEPSi as two or three extra ER features being located between 1.2 and 3.1 eV which are never observed in bulk crystalline Si. Employing a simple effective mass approximation model, we have evaluated the reduced mass, the kinetic energies and the Coulomb attraction energies of the quantumconfined e-h pairs. We also found that the energy distance between the transition energies at the ground state and the photoluminescence (PL) peak energies basically corresponds to the Coulomb attraction energies. Finally, we propose a new luminescent model based on interband transitions involving the quantum-confined dense e-h plasma.