On the Impact of Metal Impurities on the Carrier Lifetime in N-type Germanium
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0994-F09-06
On the Impact of Metal Impurities on the Carrier Lifetime in N-type Germanium Eugenijus Gaubas1, Jan Vanhellemont2, Eddy Simoen3, Antoon Theuwis4,5, and Paul Clauws2 1 Institute of Materials Science and Applied Research, Vilnius University, Vilnius, Lithuania 2 Department of Solid State Sciences, Ghent University, Krijgslaan 281 S1, Ghent, B-9000, Belgium 3 IMEC, Kapeldreef 75, Leuven, B-3001, Belgium 4 Umicore Electro-Optic Materials, Watertorenstraat 33, Olen, B-2250, Belgium 5 Present: AMI Semiconductor Belgium BVBA, Westerring 15, Oudenaarde, B-9700, Belgium ABSTRACT The impact of metallic impurities on the carrier lifetime in n-Ge is studied using microwave reflection and absorption techniques. Co, Fe, Ti, Ni and Cr are introduced by ion implantation followed by a thermal anneal and quenching to room temperature. Excess carrier decay transients are examined by microwave reflection and absorption probing after pulsed light excitation. A detailed analysis allows to evaluate the ratio of the capture cross-sections for minority and majority carriers revealing an acceptor-like character of the metal induced traps. Cross-sectional lifetime measurements show an U-shaped depth distribution with the lowest lifetimes in the bulk of the wafer. The lifetime results are correlated with those of deep level transient spectroscopy in order to clarify the properties of the dominant metal related recombination centres. Fe and Co are the most effective lifetime killers in n-Ge while Cr has the least influence.
INTRODUCTION There is a strong interest to use Ge layers as active device layers in deep submicron CMOS technology for the production of high frequency devices. In advanced silicon technology, metal films are used in various processing steps and also the use of germanides for contacting purposes is actively pursued. As metal impurities can be detrimental for carrier lifetime, there is a revival of the investigation of metal related recombination centers in Ge. Transition metals are fast diffusing contaminants in Ge and may distribute inhomogeneously within device structures and can lead to U-shaped depth profiles throughout the wafer thickness [1,2]. Several shallow and deep trap levels can be attributed to the presence of metal impurities [3]. The aim of this work is a comparative analysis of recombination characteristics in n-Ge after ion implantation with Co, Fe, Ti, Ni, or Cr, using different fluences and thermal anneals. The impact of metallic impurities on the carrier lifetime is studied by using microwave absorption and reflection transient techniques. It is shown that high densities of implantation related defects can cause a redistribution of carrier capture and recombination flows by trap filling [4-6] and can cause charge sign inversion effects when recombination processes are more complicated than the Shockley-Read-Hall mechanism. The electrical activity of the metal implantation induced recombination defects depends on the thermal anneal after metal implantation. The anneal temperature and time de
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