At present

porous silicon(PS) can be prepared by different methods.Porous silicon fabricated by anodic etching

photochemical etching and chemical etching were reported respectively

but the difference of the three methods has not yet been reported. The substrates used in this work were all n-type Si wafer with resistiv ity between 4～7Ω·cm and (100) crystalline orientation.The first sample was prepared by anodic etching method in double-cell which made of teflon.The anodic etching was carried out in a solution of HF:ethanol=1:1 at constant current density of 3mA/cm

2

at room temperature.The second sample was prepared by photochemical etching method using a 632.8nm line from a He-Ne laser of 1.5mW in the solution of the same as the first. The third sample was prepared by chemical etching method in a solution of

V

(HF):

V

(HNO

3

):

V

(H

2

O)=1:1:1.5 without current or light assistant. Formation mech anism of PS was analyzed and photoluminescence(PL) spectra of the three samples was investigated in this paper. Anodic oxidation method is the best one verified by comparing experimental setup

preparing conditions

formation mechanism and photoluminescence spectra.In addtion

free carriers play an important role in the formation process of porouss ilicon.