Photoluminescent (PL) porous layers were formed on p-type silicon by a metal-assisted chemical etching method using H2O2 as an oxidizing agent. Silver particles were deposited on the (100) Si surface prior to immersion in a solution of HF and H2O2. The morphology of the porous silicon (PS) layer formed by this method was investigated by atomic force microscopy (AFM). Depending on the metal-assisted chemical etching conditions, the macro- or microporous structures could be formed. Luminescence from metal-assisted chemically etched layers was measured. It was found that the PL intensity increases with increasing etching time. This behaviour is attributed to increase of the density of the silicon nanostructure. It was found the shift of PL peak to a green region with increasing of deposition time can be attributed to the change in porous morphology. Finally, the PL spectra of samples formed by high concentrated solution of AgNO3 showed two narrow peaks of emission at 520 and 550？nm. These peaks can be attributed to formation of AgF and AgF2 on a silicon surface. 1. Introduction The indirect band-gap structure of silicon strongly restricts its application in the area of optoelectronics. The indirect transition that requires the participation of phonons leads to the low radiative recombination efficiency and the poor luminescence property. Many efforts have been carried out to solve this physical inability. One of the possible candidate systems is silicon nanostructures such as porous silicon (PS) [1, 2], silicon nanocrystallines (SiNCs) [3–5], and silicon nanowires (SiNWs) [6, 7]. The remarkable characteristics of visible photoluminescence (PL) in porous silicon at room temperature have given great impulse to these material studies [8–10]. PL from porous silicon is observable at wavelengths ranging from ultraviolet to the infrared. PS prepared using the electrochemical method shows strong visible emission, which is considered to originate from the quantum wires in the samples. The color of luminescence light could be well controlled by the variation of the size of the SiNCs. Various mechanisms, such as quantum confinement effect, surface state, and defect-center luminescence, were proposed to uncover the luminescence origins of PS and SiNCs. It is now generally agreed that various mechanisms are responsible for the different PL bands [11, 12]. Recently, a new method, termed metal-assisted chemical etching, has been developed, which is relatively simple compared to the electrochemical method. The method does not need an external bias and enables a formation
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