Kinetics of Formation and Metastability Mechanism for Thermal Donor-Related Defects in Al-Doped Silicon

Abstract

For almost 40 years, since their discovery in the 1950's [1], thermal donors (TD) in silicon are certainly among the most studied defect systems in solids. Although much effort has been put into the investigation of this defect, the microscopic stucture and the generation kinetics of thermal donors are not fully understood [2]. Even less is known about the TD-related defects, shallow thermal donors (STD), observed for the first time in the mid eighties by photo-thermal ionization spectroscopy [3]. In the Al-doped samples a new member of the STD-family has been found, called the K-donor [4]. It is generated simultaneously with other shallow thermal donors. It has a very similar binding energy, but, in contrary to other STD, it exhibits a metastable behaviour. As it has been found only in Al-doped samples, it is believed to contain aluminium [4]. In this paper we present results of the generation kinetics of the K-donor. The creation process , of the donor is linked to a more general problem of oxygen diffusion in silicon at TD-annealing temperatures. We also attempt to explain the unusual metastable behaviour of the K-donors in terms of an entropy-driven transition. The large entropy change accompanying the metastable transition of the K-donors at low temperatures can in turn be the physical reason of the very efficient diffusion processes leading to the creation of the defect. The K-donor generation experiment was carried out with boron and aluminium doped Si samples (WASO-grade) in numerous annealing steps at 470°C