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IC STRUCTURE AND NONELECTRONIC PROPERTIES OF SEMICONDUCTORS

Diffusion of Terbium in Silicon D. E. Nazyrov^ Ulugbek National University of Uzbekistan, Tashkent, 700174 Uzbekistan ^e-mail: [email protected] Submitted September 20, 2005; accepted for publication October 31, 2005

Abstract—The diffusion of terbium in silicon in the temperature range of 1100–1250°C is studied using the direct radioisotope technique for the first time. The diffusion parameters of terbium in silicon are determined. PACS numbers: 61.72.Tt, 66.30.Jt, 81.40.Ef DOI: 10.1134/S1063782606060029

The doping of silicon with certain impurities, in particular, with rare-earth elements (REEs) is of considerable interest for developing optoelectronic structures. The REEs introduced into a silicon matrix increase the thermal and radiation resistance and make it possible to fabricate device structures with luminescent properties in a wide spectral range for the subsequent development of silicon-based optoelectronics [1, 2]. In this paper, we report the results of studying the diffusion of terbium in silicon using the direct radioisotope technique for the first time. Previously, the diffusion of this element in silicon was studied by the indirect method [3, 4] and by the neutron-activation analysis [4]. On the surface of n-Si samples (ρ = 15 Ω cm, area ~1.5 cm2, and thickness ~380 µm), we deposited a terbium-chloride layer or sputtered the layer of an impurity containing the 160Tb2O3 oxide of a radioactive terbium isotope. The cells with samples located in them were placed in an SDO-1 diffusion furnace supplied with a REPID programmed temperature controller that provided the maintenance of temperature within ±1°C. The diffusion-stimulating annealing was carried out in air, evacuated cells (~10–4 Torr), and pumped-out cells in an argon atmosphere at temperatures of 1100– 1280°C. The duration of the diffusion-stimulating annealing varied, depending on the diffusion temperature, from 5 to 72 h. After the diffusion annealing, the samples were repeatedly rinsed in fluoric acid, aqua regia, and a boiling H2O2 : HCl mixture. Such a rinsing usually enabled us to remove virtually completely the diffusion source left on the sample surface. After this, the sample edges were cleaned by etching and rinsing down to a depth of ~100 µm, which considerably exceeds the diffusion depth (~10 µm). The concentration profile of terbium in silicon was analyzed by layer-by-layer etching (in a 1HF : 50HNO3 solution with rinsing in a H2O2 : HCl mixture) and by measuring the residual activity of the sample by a UMF-1500M low-background installation

with an SBT-11 β-particle counter (Ioffe Physicotechnical Institute, Russian Academy of Science, St. Petersburg). The thickness of removed layers (0.05–0.5 µm) was determined by weighing the sample. The autoradiograms obtained before and after the annealing and during the removal of layers testified to a uniform distribution of terbium impurity over the sample cross section and to the absence of inclusions. We experimentally determine