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Deep-level-transient spectroscopy of heavily Al-doped ZnSe layers grown by molecular-beam epitaxy

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8 Author(s)
Oh, D.C. ; Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan ; Takai, T. ; Hanada, T. ; Cho, M.W.
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Using deep-level-transient spectroscopy, we have investigated deep levels in heavily Al-doped ZnSe layers grown by molecular-beam epitaxy. The Al concentration of the ZnSe layers lies in the range of 5×1018–9×1018 cm-3. The ZnSe:Al layers exhibit two electron-trap centers with the thermal activation energies of 0.16 eV (ND1) and 0.80 eV (ND2). ND2 is a dominant trap center with a trap density of 3×1016 cm-3, while the trap density of ND1 is estimated to be 2×1015 cm-3. However, ND2 shows anomalous behaviors, different from isolated point defects, in the following points: (1) the emission peak of ND2 moves to the low temperature side with increasing filling pulse duration; (2) the emission peak of ND2 is broader than theoretically calculated one for an isolated point defect; and (3) the capacitance-transient curve is nonexponential. It is observed by high-resolution x-ray diffraction that heavy Al doping results in the relaxation and plastic deformation of the ZnSe lattice. These behaviors can be ascribed to extended defects with a broad energy spectrum. By assuming a Gaussian distribution of deep levels due to extended defect, the broad emission peak is successfully simulated.

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Journal of Applied Physics  (Volume:96 ,  Issue: 12 )