High-Resolution Spectroscopy of Point Defects in Silicon
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HIGH-RESOLUTION SPECTROSCOPY OF POINT DEFECTS IN SILICON H.G. GRIMMEISS, M. KLEVERMAN AND J. OLAJOS University of Lund, Dept. of Solid State Physics, Box 118, S-221 00 Lund, Sweden
ABSTRACT The paper briefly outlines recent developments in high resolution spectroscopy of point defects in silicon. One of the methods, namely photothermal ionization spectroscopy (PTIS) is discussed in detail. Impurities induced by selenium and several transition metals are used as examples in order to illustrate the powerful scope of both transmission and PTIS measurements. These measurements are capable of providing unique information on the electronic properties of point defects, even when the defects exhibit complex excitation spectra.
INTRODUCTION The great advances in semiconductor electronics can be traced to a unique combination of basic conceptual advances, the perfection of new materials and the development of new device principles. Ever since the invention of the transistor, we have witnessed a fantastic growth in silicon technology, leading to more complex functions and higher densities of devices such as the mega bit memories. This development would hardly be plausible without an increased understanding of semiconducter materials and a better insight into the important role, defects play in most currently used devices. It is therefore not surprising that a variety of techniques for the characterization and identification of defects in semiconductors have evolved during the last few decades. Some of the earlier methods comprise electrical and magnetic measurements, photoconductivity, absorption and various forms of luminescence [1]. All these methods allowed the study of thermal "activation energies" and/or optical threshold energies but only very rarely could absolute values of fundamental electronic parameters be determined [2]. This situation has changed considerably with the introduction of junction space charge techniques (JSCT) such as photocurrent [3] and dark capacitance [4] measurements. Most of these methods, in particular deep level transient spectroscopy (DLTS) [5], allows the determination of defect concentrations with sufficient accuracy and the direct measurement of electronic parameters such as emission and capture rates. Once these parameters are known, the energy position of defects within the band gap can be determined in terms of enthalpies and/or threshold energies deduced from the distribution of a single optical cross section. There is no doubt that these measurement methods provided an important breakthrough in the characterization of defects in semiconductors. In parallel with this development fundamental improvements were achieved in defect identification [6]. If the chemical origin of the defect is unknown, defect characterization is rather meaningless. It was therefore of utmost importance to combine experimental methods for defect identification with those for defect characterization [7]. There are several basic differences between JSCT and other characterization methods which have been previo
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