ULTRAVIOLET-LIGHT FROM POROUS SILICON BY A MICROSCOPIC DISCHARGE

We discovered that some porous silicon samples show a characteristic line spectrum in the near UV and violet spectral regions. The violet part of the light can be clearly seen with the naked eye in the darkened laboratory at ambient pressure. The origin of this phenomenon is completely different from that of the known luminescence of this material in the visible region and the near IR. While visible luminescence starts at voltages of some volts, UV line emission starts at a threshold voltage of about 80 V. The UV spectrum emitted from porous silicon is identical to the spectrum of a low-pressure RF N-2 plasma (for the resolution of the spectrograph), thus proving that a stable plasma discharge can be established in the pores of porous silicon. Especially at higher voltages, ozone is produced. In this paper we present some of the fundamental optical and electrical properties of the samples and suggest a model for the origin of the plasma discharge.