Semiconductor Optics 1 by Heinz Kalt & Claus F. Klingshirn

Author:Heinz Kalt & Claus F. Klingshirn
Language: eng
Format: epub
ISBN: 9783030241520
Publisher: Springer International Publishing

18.1.3 Deep Defects and Related Radiative Transitions

Apart from the shallow donor and acceptors there are deep donors and acceptors as mentioned already above and a variety of other deep centers.These are atoms which have one or more energy levels somewhere around the middle of the gap. See e.g., [82L1, 01H1].

For deep centers an approach as in (18.2) is not adequate. The wave function is better described by the parent atomic orbitals, modified by the influence of the surrounding atoms, i.e., by the symmetry of the arrangements of the neighbors. Examples of this type of center are copper, sodium, the rare earths, and the transition metals. They give rise to the green, orange and red emission bands of wide-gap semiconductors such as CdS, ZnO and ZnS [67S1, 76T1, 01L1, 10H1, 10M1].

Carriers in deep centers can sometimes couple strongly to bulk and/or localized phonon modes giving rise to very broad emission (and absorption) features with Huang-Rhys factorsS significantly larger than 1. We give an example in Fig. 18.3. The phonon structure, which is characteristic for this luminescence band allows determining the Huang-Rhys factor for this Cu centre in ZnO to be 6.5.

Fig. 18.4Deep center emission of ZnO:Cu

(reprinted with permission from [81K1] ©1981 Elsevier)

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