Er-Doping in Silicon by Pulsed Laser Irradiation
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Er-DOPING IN SILICON BY PULSED LASER IRRADIATION
KENSHIRO NAKASHIMA Nagoya Institute of Technology, Department of Electrical and Computer Engineering, Showa-ku, Nagoya 466, Japan
ABSTRACT Erbium ions were successfully doped in silicon by pulsed laser irradiation above the threshold laser energy density. Photoluminescence peaks at 1.54, 1.59 and 1.64 [tm from Er-optical centers were observed after annealing of Er-doped samples. The intensity of the 1.54 ugm Er-emission band increased upon increase in the laser energy density, and then gradually decreased after reaching the maximum, due to the laser sputtering of the silicon substrate. Oxygen atoms, which were unintentionally codoped with Er-ions, were found to be distributed in the same region as in Er-ions, and were suggested to play roles to activate Er-optical centers. The maximum concentration3 of Er-ions doped in the solid state regime were estimated to be the order of 1018 cm- by the Rutherford backscattering measurements. INTRODUCTION Rare-earth ions in semiconductors have a potential for development of optoelectronic integration. Especially Er in Si has attracted an attention for its features to emit sharp luminescence ( PL ) at 1.54 [tm under optical excitation or electronic injection. Several methods have been applied to dope Er atoms into Si substrates; ion implantation[1], molecular beam epitaxy [2] and doped crystal growth [3]. In spite of much efforts to realize intense luminescence in high efficiency, none of the methods are successful as yet in obtaining Er-doped Si with high performance. In this paper a new method using pulsed laser irradiation is described to be applicable for doping Er ions into Si substrates. This method requires only a pulsed laser ( a dye laser in this case ) with high enough output energy for doping. Laser fluences are restricted not to exceed a critical value to melt Si surface. We, therefore, are concerned in the present experiment with the impurity-doping in the solid state regime. Since the pulsed laser irradiation on commercial grade floating zone ( FZ ) Si, which contains little amount of oxygen and carbon impurities, is essentially a defect-free process [4], as far as PL and DLTS studies concerned, this doping method does not necessarily require high temperature anneal to remove process-induced defects. In spite of this fact, heat-treatment is necessary for enhancing the PL intensity from Er ions. The PL, the secondary ion mass spectrometry ( SIMS ) and Rutherford backscattering measurements ( RBS ) are used to detect Er ions doped and their depth profiles. The PL intensity at 1.54 im and the amount of doped Er ions are found to be dependent on the fluences of the incident pulsed laser. EXPERIMENTAL Samples used are mainly phosphorus-doped floating-zone ( FZ ) Si of a commercial grade ( 15 f2cm). After cleaning mirror surfaces with a solution of NH 4OH and H 20 2, erbium with 4 ninespurity was deposited in a vacuum at 5x10- 6 Torr. One shot from a pulsed dye laser ( wave length; 584nm, pulse width; 500ns ) was inciden
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