Characteristics of Light Emission by Ballistic Electron Excitation in Nanocrystalline Silicon Device Formed on a p-Type Substrate

Abstract

It is demonstrated that planar light emission by ballistic electron excitation is observed in a nanocrystalline porous silicon (nc-PS) device fabricated on a p-type silicon substrate and occurs in a similar way to the case of n-type substrate. The device is composed of a semitransparent thin Au film, an organic fluorescent film, the nc-PS layer, a p-type Si substrate and an ohmic back contact. When a positive bias voltage higher than 20 V is applied to the Au top contact, the diode uniformly emits green light. The light intensity sharply increases with increasing bias voltage. The measured luminescence band coincides well with the original photoluminescence spectrum of the deposited fluorescent material. A hysteresis is observed in the current-voltage and the corresponding luminescence-voltage characteristics. These optoelectronic properties suggest that the light emission is based on excitation of a fluorescent film by ballistic electrons generated in the nc-PS layer. The observed hysteresis is due to an optical feedback effect by which photoexcited electrons in the nc-PS layer participate in the ballistic transport and subsequent impact on the fluorescent film. The present result is useful for applications to functional planar light-emissive devices.