Interband Optical Transitions

The conduction-band splitting into two nonparabolic subbands predicted by the BAC model has been unambiguously observed in GaNxAs1−x and Ga1−yInyNxAs1−x using photomodulation spectroscopy [26,42,43]. Figure 2.4 shows photoreflectance (PR) spectra recorded from GaNxAs1−x samples. The PR spectrum of GaAs (x=0) exhibits two sharp derivativelike spectral features corresponding to the transition from the top of the valence band to the bottom of the conduction band (E0 transition), and the transition between the spin-orbit split-off band and the conduction-band minimum (E0+Δ0 transition). For N-containing samples, in addition to the PR spectral.

features related to the transition across the fundamental band gap (E− transition) and the transition from the top of the spin-orbit split-off valence band to the bottom of the conduction band (E−+Δ0 transition), an extra feature (E+) appears at higher energies in the PR spectra. With increasing N concentration, the E− and E−+Δ0 transitions shift to lower energy, and the E+ transition moves in the opposite direction. Shown in Figure 2.5 are the E− and E+ transition energies in Ga1−yInyNxAs1−x as a function of N concentration reported by several different groups [41,43–45]. The nonlinear dependence of the transition energies on N concentration can be well described by the BAC model using a coupling constant V=2.7 eV.

It is also worth noting that, as shown in Figure 2.4, the spin-orbit splitting energy Δ0 is equal to ≈0.34 eV for all the measured samples and does not depend on N content. The results demonstrate that incorporation of N into GaAs and GaInAs affects mostly the conduction band and has a negligible effect on the electronic structure of the valence band. Using Equation 2.9, one can obtain a simple relationship between the subband-

ROSSANA HERNANDEZ

electrónica del estado solido

http://www.routledge.com/books/details/9781591690191/

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