Blue Light Emission from Porous Silicon
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BLUE LIGHT EMISSION FROM POROUS SILICON
X.Y.HOU, G.SHI, W.WANG, F.L.ZHANG, P.H.HAO, D.M.HUANG, X.F.JIN AND XUN WANG Surface Physics Laboratory, Fudan University, Shanghai 200433, China
ABSTRACT Through a post treatment of light emitting porous silicon in boiling water, a large blue shift of its photoluminescence (PL) spectrum has been observed and a stable blue-green light emission at the peak wavelength down to 500 nm is achieved. The effect of boiling water treatment is suggested to be a kind of oxidation, which could reduce the size of the Si column, fill up some micropores and strengthen the Si skeleton. The photoluminescence microscopic observation shows that the surface of blue light emitting porous silicon is composed of many small uniformly light-emitting domains at the size of several tens of pim. Fourier transform infrared reflection (FTIR) measurements show that the formation of Si-H bonds is not responsible for the visible luminescence in the very thin Si wires.
INTRODUCTION The recent discovery that highly porous silicon (PS) can efficiently emit visible light at room temperature has drawn a great deal of attention mainly due to the potential applications in realizing all Si-based optoelectronic integration.' The exact mechanism of the luminescence from PS has not been fully revealed. The quantum confinement effect2 seems to be the most likely one although there are still some controversies. One of the problem which confuses people to believe the quantum confinement mechanism is the lack of evidence that blue light from PS can be achieved. Using ordinary HF anodic etching, one can observe the light emission from PS in the red, orange and yellow colour ranges. It has been found that some post anodic treatments such
Mat. Res. Soc. Symp. Proc. Vol. 283. 01993 Materials Research Society
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as oxidation in air, electrochemical oxidation under anodic bias and rapid thermal heating in 02 could reduce the effective size of the Si rods in PS and cause a blue shift of the photoluminescence(PL) spectrum. 3..45 .6 However, all these treatments did not result in a large scale shift which moves the emitting light into the blue. Up to now, the shortest peak wavelength of PL spectrum is 530 nm, which is in the green colour range. The demonstration of blue light emission is of great importance for both supporting the quantum confinement hypothesis and realizing full colour display by PS. In this paper we present a simple post anodic treatment which could lead to a large scale blue shift in the photoluminescence spectrum of PS. A PL peak wavelength of 500 nm has been achieved.
EXPERIMENTAL The porous silicon samples were prepared by anodic etching p-type Si wafers ( orientation, 18-23 Q.cm) in a mixture of HF:CH 3CHIOH=l :1 at a current density of 5 mA/cm 2 -10 mA/cm 2 for about 30 minutes to 90 minutes. Under the illumination of an ultraviolet (UV) lamp the as-etched samples emitted red, orange, yellow or even green light according to different etching conditions. Then the sample was immersed in boiling deioniz
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