(Color online) AFM images of the uncovered (a) QWR sample and (b) QDC sample. The upper panel is the shape of the cross section of wires at the position of the line in (a).
The CER spectra (dashed) of the (a) QDC and (b) QWR samples measured at low temperatures. The quantum confinement transition energies are obtained by using the first derivative Lorentzian profile for QDCs and the Gaussian profile for QWRs (solid lines).
The CER spectra of the QDC sample measured from the backside of the sample with (solid) and without (dashed) epitaxtial layers. The band gap of the unstrained GaAs substrate is determined to be at and at , as indicated by the arrows. The spectrum at is shifted upward for clarity.
The CER spectra (dashed) of the (a) QWR sample and the (b) QDC sample in the energy range of GaAs absorption at low temperature and at room temperature . The arrows indicate the transition energies obtained through fitting by using Lorentzian profile , with . The band-gap energies [ at and at ] of unstrained GaAs are used in the fitting. The spectrum of the QWR sample is shifted upward for clarity.
The SPV spectra of (a) the QDC and (b) the QWR samples measured at higher temperatures. The insets show the first derivative of the SPV signals. The band gap of unstrained GaAs is indicated by the arrows in the insets.
Various transition energies obtained by fitting the experimental CER curves using the Gaussian profile for the QWR sample and Lorentzian profiles for the QDC sample. The calculated values are obtained in the case of quantum well using the envelope-function model (Ref. 1). In the calculation, , , , and . All values for InGaAs are obtained by linear extrapolation between GaAs and InAs. The lattice mismatches between and GaAs are 2.1% and 3.2% for and 0.45, respectively.
Transition energies obtained from the fitting CER spectra by using the Lorentzian profiles in the energy range of the GaAs band gap. (GaAs) is the band gap of bulk GaAs, which was obtained from the CER at in Fig. 2(a). The experimental band-gap change , the average (fundamental) band-gap change , and the VB splitting are also computed.
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