Transient behaviour of the strong violet electroluminescence of Ge-implanted SiO2 layers

Si-based light emitters will be a key element of future optoelectronics. One of the most promising approaches is Ge-implantation into thin SiO2 films on crystalline Si. This system exhibits a strong violet electroluminescence with a power efficiency up to 0.5 % [L. Rebohle et al., J. Electrochem. Soc.: Electrochem. and Solid State Lett. 7 G57 (2001)], but the mechanism of electrical excitation is not yet fully understood. In this paper the electrical excitation of the luminescence centers is investigated by means of electrical and electroluminescence transient measurements. It is found that the most probable way to excite luminescence centers is the impact excitation by hot electrons. Whereas the injection is explained by trap assisted tunneling of electrons from the substrate into the oxide, the electrons will be transported via traps or in the SiO2 conduction band. Furthermore, the electroluminescence rise and decay time is estimated to be of the order of 100 microsec.