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LUMINESCENCE PROPERTIES OF POROUS SILICON C. Peng1 , L. Tsybeskov'2 and P.M. Fauchet1 1 Department of Electrical Engineering, University of Rochester, Rochestcr NY 14627 2 Department of Physics & Astronomy, University of Rochester, Rochester NY 14627 ABSTRACT We report the results of a systematic study of the influence of the anodization and etching conditions, and chemical and thermal treatments on the properties of light-emitting porous silicon (PSI). PSI layers with stable, high efficiency photoluminescence (PL) tunable from the near infrared to the yellow have been obtained using p-type and n-type substrates. As the temperature drops below 100 K, the as-anodized PSI layers display striking changes in the PL spectra, which are absent in PSI layers that have received a post-growth treatment.

INTRODUCTION Two years after Canham's discovery [1] of bright, visible photoluminescence (PL) from porous silicon (PSI), it is well established that the PL efficiency of PSI is comparable to that of direct gap IHI-V semiconductors [2]. PSI has several advantages over IlI-V compounds: ease of fabrication, low cost, and potential compatibility with silicon microelectronics. PSI could therefore emerge as a serious challenger in several technologies, from displays to optical interconnects. However, before technological applications of PSI become reality, two obstacles must be overcome: the origins of light emission must be established beyond doubt and the degradation of the luminescence must be eliminated. PSI is a complex. inhomogeneous material, in which different types of structures and chemical bonds coexist. Several models have been proposed to explain the unexpected PL of PSI. The quantum size model [1] attributes the light emission to nanocrystalline Si structures formed during electrochemical etching and anodization. In this model, the electrons and the holes are confined to pillars having a diameter < 10 nm. As a result, the radiative lifetime decreases compared to that in bulk silicon and the effective bandgap opens because of quantum confinement [3]. Several alternatives have been proposed, including light emission from siloxene [4] or others polymeric-like Si compounds, and light emission from H-rich amorphous silicon [5]. Most of the experimental and theoretical evidence seems to strongly favor the quantum size model. The most vexing property of PSI is that its bright PL degrades under illumination, slowly in vacuum or inert atmospheres with visible light, much more quickly in laboratory air or oxygen with UV light [6]. This degradation is related to the de-passivation of the surface of PSI, which, in the as-prepared samples, is covered with hydrogen. Hydrogen passivation eliminates nonradiative recombination centers associated with dangling bonds on the surface, leading to high PL efficiency (> 1%) and long PL lifetime (> l~isec) [2]. Elimination of the PL degradation haes not yet been achieved and ways to reach this goal are actively pursued by many groups, including ours. In this paper, we report some results of