Parts | Days | Selection | Search | Downloads | Help
HL: Fachverband Halbleiterphysik
HL 28: Optical properties
HL 28.5: Talk
Wednesday, March 28, 2007, 15:15–15:30, H14
Carrier Capture by Ionized Impurities in ZnO Epilayers — •Frank Bertram, Juergen Christen, Armin Dadgar, and Alois Krost — Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg, Universitaetsplatz 2, 39106 Magdeburg
The kinetics of relaxation and recombination processes of excitons in an epitaxial-grown thick ZnO layer has been examined using time-resolved cathodoluminescence. The unique feature of this technique allows the full analysis of excitation from thermal equilibrium into true steady state condition and the subsequent relaxation back into thermal equilibrium. The high quality 8 µm thick ZnO epi-layer under study was grown by MOVPE on an optimized ZnO/GaN/sapphire template. At T = 4 K the luminescence is dominated by the impurity bound exciton (BE) I8. The free exciton XA, the BEs I1, I2, and I6, as well as I9 are clearly visible. No spectral shift with time is observed for all excitons - neither during onset nor during decay. However, a distinct change in intensity ratio of I8 and I9 as compared to I1 and I2 is found in time delayed spectra. The excitons bound to a neutral impurity I8 and I9 exhibit a delayed, strictly mono-exponential decay over three orders of magnitude which is initially fed by the capture of the free exciton XA (τloc≥ 95 ps). In complete contrast, the ionized impurity bound excitons I1 and I2 show a non-exponential decay starting with a very fast initial decay followed by a slower component exhibiting strong persistence. The fast initial drop results from the carrier capture by the ionized donors (τcapture(I1,2)≥ 300 ps) resulting in their neutralization - thus feeding the neutral bound excitons.