Annealing Studies of Visible Light Emission from Silicon Nanocrystals Produced by Implantation
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(a),
B. Nielsen
('a,
L. F. Di Mauroco), B. Sheey (bl,P. Muttilc), A. Pifferi'c), P.
Taroni (r,L. Valentini (c),F. Comi
(d),R.
Tonini (d)
(a)Department of Applied Science, Brookhaven National Laboratory, Upton, N.Y. 11973 (b)Department of Chemistry, Brookhaven National Laboratory, Upton, N.Y. 11973 (c)Dipartimento di Fisica, Politecnico di Milano, 20133 Milano Italy (d)Dipartimento di Fisica, Universita di Modena, Modena, Italy
ABSTRACT The annealing behavior of silicon implanted Si0 2 layers is studied using continuous and timegated photoluminescence (PL). Two PL emission bands are observed. A band centered at 560 nm is present in as implanted samples and it is still observed after 1000 TC annealing. The emission time is fast (0.2 -2 ns). A second band centered at 780 nm further increases when hydrogen annealing was performed. The emission time is long (1 4ts - 0.3 ms). INTRODUCTION Ion implantation is a promising technique for producing silicon nanocrystals (Sinc) in a dielectric matrix. The basic idea in this approach is to enrich by ion implantation the silicon concentration in a dielectric matrix. Subsequent thermal annealing can promote the formation of crystalline precipitates having nanometric dimensions. Ion implantation which is a well established technique in microelectronics, presents some extra advantages: the control of the depth and width of the region of Sinc formation, and the possibility to implant different ions in different substrates. Photoluminescence (PL) from Sinc produced by ion implanation has been reported by several authors [1-4]. Shimizu-Iwayama et al. [2] presented data of room temperature luminescence from 1 Mev Si' implanted fused silica. Komoda et al. [3] observed a band centered at 600 nm, and a red shift that was interpreted as due to an increase in the size of Sinc. The observation of near infrared and blue-green light emission in Si0 2 layers implanted at 1 x 1017 cm-1 and annealed at high temperature (T>1000 °C) has been reported by some of us [4- 6]. In spite of the many investigations, a complete study of the kinetics of formation of the two emission bands as a function of different preparation conditions, and of their emission times has not been performed. This study could provide a better understanding of the physical parameters which influence the luminescence mechanism. At the same time, this can also be of pratical interest to improve the PL intensity in view of possible optoelectronics applications. To address some of these issues, in this paper continuous and time-gated PL studies of Si+ implanted SiO 2 layers were performed starting from as-implanted samples. EXPERIMENT Samples were prepared by implantation of 160 KeV 28Si+ ions into 430 nm thick Si0 2 layers thermally grown on a (100) oriented p-type Si substrate. Fluences ranged from 3 x 1016 105 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
cm 2 to 3 x 1017 cm"2 . Vacuum annealing was performed in a high-vacuum chamber (10-7 torr) and the sample was mounted on a resistively heated ta
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