Electronic properties of interstitial iron and iron-boron pairs determined by means of advanced lifetime spectroscopy

Abstract

As dissolved iron is one of the most common lifetime-killing contaminants in silicon, its coexisting defect configurations, interstitial iron (Fei) and iron-boron pairs (FeB), are investigated on an intentionally iron-contaminated silicon sample by means of temperature-dependent lifetime spectroscopy (TDLS) and injection-dependent lifetime spectroscopy (IDLS). In good agreement with the literature, the study identifies the known Fei donor level at Et−EV=(0.394±0.005)eV and determines its symmetry factor as k=σn∕σp=51±5, which is an order of magnitude lower than expected from the literature. Using the well-confirmed k factor, the poorly confirmed electron-capture cross section is redetermined as σn=(3.6±0.4)×10−15cm2 at 300K. In addition, the observed exponential σ(T) dependence identifies the multiphonon emission mechanism as the dominant capture mechanism for electrons with an activation energy E∞=0.024eV. Concerning the defect related to the iron-boron pair, the study unambiguously identifies the deep FeB acceptor level as the dominant FeB recombination center. While the known average value EC−Et=(0.26±0.03)eV for the energy level is well confirmed, the symmetry factor is determined as k=0.45, which represents an intermediate value among the scattered results from the literature. Additional spectroscopic information from the defect transformation allows both capture cross sections of the FeB defect to be determined (σn=2.5×10−15cm2 and σp=5.5×10−15cm2). Being suggested as a fingerprint of iron in the literature, the crossover position of the Fei- and FeB-dominated IDLS curves (at 300K) is experimentally proved to be doping dependent which is accurately predicted on the basis of the extracted set of Fei and FeB defect parameters. An additional fingerprint of iron is found by the qualitative change of the TDLS curve upon illumination and its S-like shape under dark conditions, which represents a robust criterion for unambiguous identification of iron in silicon. As the most sensitive technique to detect and determine an iron contamination in silicon heavily relies on the Fei and FeB defect parameters, the spectroscopic results are of special practical importance.