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The PL spectra for samples K0687 and K0688 and the absorption spectrum for K0687 measured at with a FTIR Nicolet Magna 6700. The excess carriers were excited with a diode laser at a power density of . The PL spectra correspond to transitions from the bottom of the conduction band to the top of the valence subband C-V1; C-V2 in the absorption spectrum denotes transitions from the top of the second valence subband to the bottom of the conduction band.
The TRPL spectra for K0687 showed in a range of excitation pulse energy from 2.3 to 23 nJ. The excitation area was . The peak excess carrier concentration for the lowest decay was estimated to be . The inset shows the dependence of the peak PL intensity on excitation energy. The quadratic dependence indicates that the excess carrier concentration was above the background doping level.
The PL frequency responses of K0687 to a small-signal sin-wave modulated excitation for two continuous-wave power levels of 5.5 and 9.8 mW. The excitation area was . The inset shows power dependences of both the inverse decay constant and the low-frequency PL response. The minority carrier lifetime of 80 ns was determined by extrapolation to zero excitation level. A rapid increase in the PL response indicated that the background carrier concentration was below the minimum excess carrier concentration estimated to be .
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