ESR Study of Porous Silicon
- PDF / 318,220 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 78 Downloads / 237 Views
ESR STUDY OF POROUS SILICON W.Y. Cheung*, S.P. Wong*, I.H. Wilson*, C.F. Kan**, and S.K. Hark** *Dept. of Electronic Engineering and Materials Technology Research Centre, The Chinese University of Hong Kong, Hong Kong. **Dept. of Physics and Materials Technology Research Centre, The Chinese University of Hong Kong, Hong Kong.
ABSTRACT A detailed ESR study has been performed on porous silicon on both and p-type silicon substrates prepared using anodization in HF under a range of conditions and the results are correlated with the light emission properties. It is found that the ESR spectra are dependent upon the orientation of the samples. The ESR defect centers are identified to be the Pb centers or PbO centers of the Si-SiO2 system from the g-value anisotropy maps. The variation of the spin density N with annealing conditions has also been studied for samples annealed either in nitrogen or oxygen ambient at 2000C for various time intervals. It is concluded that the increase or decrease of N are due to the generation or elimination of the Pb or Pb0 centers in conjunction with the oxidation process during annealing. From PL study of these samples, it is found that there is no simple correlation between the spin density and the PL intensity. However, a blue shift in the PL peak position was observed both in samples after a post-annealing etch in HF solution, and in samples annealed in oxygen without a post-annealing etch. This blue shift supports the quantum confinement model of light emission from porous silicon.
INTRODUCTION Since the discovery of efficient visible photoluminescence (PL) at room temperature from porous silicon prepared by anodization in HF [1, 2], a lot of work has been done to study the physical properties of porous silicon and the physical mechanism of such strong light emission from porous silicon [1-7]. One popular model suggests that the efficient PL is due to a quantum size effect [2] but another model suggests that the origin of the strong PL is identical to that in siloxene [3]. Recently. there has been some reports on ESR measurements on porous silicon [4-7] and the appearance of the ESR signals has been discussed in connection to the quenching of the PL signals. In this work, we shall report our recent results of ESR measurements on porous silicon and discuss the origin of the ESR signals. However, we shall show that there is no simple correlation between the spin density of the ESR signals and the PL intensity.
EXPERIMENT Both p-type Si wafers of 0.35-0.7R cm and p-type Si wafers of 0.15-0.25 Qcm have been used in this work for the preparation of the porous silicon by anodization in 50% HF solution. The anodization cell is a double cell with the wafer placed in between the two half cells. The 2 samples were anodized using a current density of 10 mA/cm for 2, 8, 15 or 30 minutes. After anodization, the samples were rinsed in de-ionized water and then blown dry with nitrogen. Thermal annealing was performed either in nitrogen or in oxygen at 2000C for various time intervals. After ESR mea
Data Loading...
