Defects in MBE-grown Silicon Epilayers Studied with Variable-Energy Positrons
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DEFECTS IN MBE-GROWN SILICON EPILAYERS STUDIED WITH VARIABLE-ENERGY POSITRONS P.J.SIMPSON,
Dept.
P.J.SCHULTZ,
of Physics,
I.V.MITCHELL,
T.E.JACKMAN
University of Western Ontario,
and G.C.AERS.
London,
Ontario N6A 3K7,
ýanada.
Microstructural Sciences Laboratory, Ottawa, Ontario KIA OR6, Canada.
National Research Council
of Canada,
ABSTRACT Few non-destructive techniques are available which provide information regarding defect type, concentration and depth distribution in semiconductors. The variable-energy positron beam technique has recently demonstrated a at low defect impurities surface defects and sensitivity to near concentrations. In the present study, intrinsic silicon (100) epilayers of -3000 A thickness grown by MBE at different temperatures were examined by this method for evidence of changing defect concentration and type. INTRODUCTION Molecular beam epitaxy (MBE) is a well established method for growing semiconductor epilayers of high purity and crystal perfection, yet it may still result in defect concentrations that can affect the electronic properties of these epilayers. For example, recent photoluminescence [1] and deep level transient spectroscopy [2] measurements have provided evidence of in intrinsic silicon grown at low significant defect concentrations temperatures (s500*C). It is apparent that the characterization and control of such defects would benefit from improved methods for identifying defect type, concentration and distribution. As an emerging technique for defect measurement, positron annihilation offers several advantages for studying the near-surface defect distribution [3]. The technique is non-destructive, provides depth-resolved information, and is sensitive to concentrations of point defects as low as 10-6 per atom. Qualitative and comparative interpretation of positron beam results is relatively straightforward. Quantitative analysis is more difficult, but progress is being made in its development [4]. In this paper we discuss results of a preliminary study of multilayer silicon samples grown by molecular beam epitaxy (MBE) at the National Research Council of Canada (NRC). The application of the slow positron technique to single semiconductor epilayer structures is well established [5,61; in this study we apply positron annihilation to one and two epilayer structures, each grown at different temperatures. Data were also obtained using secondary ion mass spectroscopy (SIMS) and electrochemical current-voltage (eCV) profiling as a check on sample impurity content. EXPERIMENTAL METHOD AND ANALYSIS Details of the slow positron beam apparatus at the University of Western Ontario are given in reference 17]. Monoenergetic positrons (in the range 0.1 to 60 keV) are implanted into the sample to be studied and lose energy by (le. mechanisms similar to those for electrons. After "thermalization" reaching thermal energy), the positron diffuses through the solid until it annihilates, with a typical lifetime of -200 picoseconds. Annihilation can occur in the defect-free solid,
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