Grown-in and Radiation-induced Defects in 4 H -SiC
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Grown-in and radiation-induced defects in 4H-SiC T. A. G. Eberlein and R. Jones School of Physics, University of Exeter, Exeter, EX4 4QL, United Kingdom P. R. Briddon Department of Physics, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, United Kingdom ¨ S. Oberg Department of Mathematics, University of Lule˚ a, Lule˚ a, S95 187, Sweden ABSTRACT SiC is a material that seems ideal for high-power, high frequency and high temperature electronic devices. It does not suffer from large reverse recovery inefficiencies typical for silicon when switching. In contrast to silicon, SiC is however difficult to dope by diffusion, and instead ion-implantation is used to achieve selective area doping. The drawback of this technique is that irradiating the crystal with dopant atoms creates a great deal of lattice damage including vacancies, interstitials, antisites and impurity-radiation defect complexes. Although many of the point defects can be eliminated through thermal annealing, some however, e.g. the photoluminescence (PL) DI and DLTS Z1 /Z2 centers in 4H-SiC, are stable to high temperatures. In this polytype, DI and the related alphabet lines are the most prominent PL signals. The latter can be seen directly after low energy irradiation while DI usually dominates the PL spectrum of implanted and irradiated SiC after annealing. Not only implantation but also rapid growth of SiC by CVD methods leads to a deterioration in quality with an increase in electrically active grown in defects. Among these, the Z1 /Z2 defects are dominant in n-type 4H-SiC, as well as material that has been exposed to radiation. We use first principles density functional calculations to investigate defect models for the above mentioned defects in 4H-SiC and relate their electrical and optical activity to experiments. INTRODUCTION Recent electron irradiation experiments have given new insight into the type of defects formed in SiC. Although many photo-luminescence PL and deep level transient spectroscopic DLTS experiments have been carried out we emphasize here experiments that use e-radiation with energies less than ∼250 keV so that only damage on the carbon sublattice occurs [1]. We expect then VC , Ci and anti-site pairs CSi –SiC to form along with complexes of these both with and without impurity complexes. We review first the work on the alphabet and H-lines which we believe can be explained by anti-site pairs and a hydrogen-anti-site complex respectively. The former is detected in eirradiated material and the latter in H-implanted material. Then we discuss a PL line called P0 -T0 whose local modes and zero-phonon line are strong evidence for Ci –CSi defects [2]. What is remarkable is that these defects are created by room temperature irradiation and some are formed outside the irradiation zone. This is evidence for a long range diffusion of Ci at room temperature and an ability to complex with anti-sites. Presumably this happen as the anti-site pair is made near to Ci so complexing has a strong possibility. A number of
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