Electronic properties of iron-boron pairs in crystalline silicon by temperature- and injection-level-dependent lifetime measurements Jens E. Birkholz and Karsten Bothe Institut für Solarenergieforschung Hameln/Emmerthal (ISFH), Am Ohrberg 1, D-31860 Emmerthal, Germany Daniel Macdonald Department of Engineering, The Australian National University, Canberra, ACT 0200, Australia Jan Schmidt a Institut für Solarenergieforschung Hameln/Emmerthal (ISFH), Am Ohrberg 1, D-31860 Emmerthal, Germany Received 7 December 2004; accepted 1 March 2005; published online 3 May 2005 Iron-boron pairs in crystalline silicon are studied by measuring the recombination lifetime as a function of injection density, doping concentration, and temperature. The characteristic crossover point of the injection-level-dependent carrier lifetime curves measured before and after optical dissociation of the iron-boron pairs is analyzed to determine the energy level as well as the electron- and hole-capture cross sections of the acceptor level of iron-boron pairs, assuming known recombination parameters for interstitial iron. The doping concentration dependence of the crossover point gives an electron-capture cross section of 1.4±0.2  10 -14 cm 2 , while the temperature dependence results in a hole-capture cross section in the range from 0.5  10 -15 to 2.5  10 -15 cm 2 and an energy level of 0.26±0.02 eV below the conduction-band edge. © 2005 American Institute of Physics. DOI: 10.1063/1.1897489 I. INTRODUCTION The recombination properties of iron and iron-boron pairs play an important role in silicon device technology. 1 FeB pairs occur naturally in iron-contaminated, boron-doped p-type silicon wafers as an equilibrium state. These pairs can be dissociated by energy supply e.g., illumination, current injection, or heating into positively charged interstitial iron Fe i +  and negatively charged substitutional boron B s - . After ceasing the energy supply, the equilibrium state is reached due to an association process, driven by Coulombic attrac- tion between the mobile interstitial iron and the immobile substitutional boron ion. 1,2 As recently reviewed by Istratov et al. 3 deep-level transient spectroscopy DLTS shows that there are at least two different energy levels related to FeB pairs, one shallow donor level at E V +0.1 eV and one accep- tor level between E C - 0.23 and E C - 0.29 eV. The latter state is believed to be the dominant recombination center, as it is deeper. In order to characterize any defect and its impact on the bulk lifetime, the electronic defect parameters, i.e., the en- ergy level and the capture cross sections, must be known. While the electronic properties of isolated interstitial iron Fe i  are well established, 2 the scatter in the experimentally determined recombination parameters of the acceptor state of FeB pairs is very large. 4,5 Injection-level-dependent lifetime spectroscopy has been applied recently in several defect characterization studies, because of its high sensitivity to electronically active recombination centers in the silicon band gap. 4,6,7 Applying this measurement technique to boron-doped iron-contaminated silicon wafers results in very different injection-level-dependent lifetime curves for the dissociated and the associated FeB state, leading to a well- defined characteristic crossover point. 8 The simultaneous determination of the three FeB param- eters, i.e., the electron- and hole-capture cross sections  n FeB and  p FeB and the energy level EFeB, by fitting the injection-level-dependent experimental curves using Shockley–Read–Hall SRH theory 9,10 is ambiguous and suf- fers from large uncertainties, particularly because additional knowledge about the total iron concentration is necessary. Therefore, in this paper we apply an approach, which is independent of the total iron concentration, to determine the acceptor energy level and capture cross sections of FeB pairs by analyzing the position of the crossover point as a function of doping level and temperature. Our method only utilizes the accurately known electronic parameters of interstitial iron, which can be regarded as an internal calibration stan- dard. II. THEORY Comparing the injection-level-dependent lifetime curves for the dissociated Fe i  and associated FeB state, one ob- serves a very different injection-level dependence for these two states in the following denoted by “as” and “dis” lead- ing to a characteristic crossover point. At this point the car- rier lifetimes of both states are equal:  as =  dis . 1 Since both Fe i and FeB are very effective recombination cen- ters, we consider only SRH recombination and neglect all a Electronic mail: j.schmidt@isfh.de JOURNAL OF APPLIED PHYSICS 97, 103708 2005 0021-8979/2005/9710/103708/6/$22.50 © 2005 American Institute of Physics 97, 103708-1 Downloaded 03 May 2005 to 150.203.45.136. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp