Dresden 2006 – scientific programme
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HL: Halbleiterphysik
HL 14: II-VI semiconductors I
HL 14.6: Talk
Tuesday, March 28, 2006, 12:15–12:30, POT 151
Resonantly and Non-Resonantly Excited Bound Excitons in ZnO Epilayers — •Frank Bertram, Sören Giemsch, Jürgen Christen, Armin Dadgar, and Alois Krost — Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg, Germany
The photoluminescence (PL) spectrum of ZnO exhibits a rich excitonic structure in the near bandgap region at 4K. A 8 µm thick ZnO epi-layer MOVPE grown on a GaN / sapphire template was investigated. The non-resonant PL spectrum is dominated by the impurity bound exciton I8 and exhibits further individual BE lines (I1, I2, I6, I9), the TES-lines of I8 and I9 as well as the LO phonon replica exclusively from I8. Under resonant excitation, i.e. Eexcitation= E(I8) the TES-I8 line and the I8-LO line are much more intense and reveal a smaller line width. Under excitation at the spectral position of I9 the optical features associated with I8 completely disappear, while TES-I9 increases and I9-LO shows up. Resonantly excited time-resolved PL yields a mono-exponential decay with lifetimes τ(I8)=270 ps and τ(I9)=280ps, respectively, - distinctively different from the lifetimes obtained for non-resonant excitation. Measuring the decay lifetime as a function of tuned laser photon energy, both, I8 and I9 reveals a clear resonance, i.e. drop in time constant (< 200 ps), for Elaser-EBE=5 meV. This corresponds to the A-B-valence band splitting and indicates strong scattering into the B-valence band.