AbstractWe use resonance Raman scattering (RRS) and electroreflection (ER) measurements to profile the the composition and strain variations in laterally composition-modulated (CM) GaP/InP short-period superlattices (SPS's). The ER spectra of a GaP2.2/InP2.0 SPS give the fundamental band-gap energy at 1.69±0.05eV, which is about 210 meV lower than the band gap energy of a GaInP random alloy with the same overall composition. The RRS measurements reveal strong dependences of the phonon spectrum on the polarization and the excitation energy. In RRS spectra measured with the polarization of both excitation and scattered photons along the composition modulation direction, the GaP-like longitudinal optical (LO) phonon redshifts by 4.0±0.5 cm−1 near the resonance with the fundamental energy gap. On the other hand, when the polarizations are orthogonal to the composition modulation, the LO phonons redshift as much as 16 cm−1 at low excitation energies. A comparison of the experimental data with a model calculation gives the average In composition in the In-rich region as 0.70±0.02, and the average Ga composition in the Ga-rich region as 0.68±0.02. Our result also indicates that there are small volumes (less than 1% volume fraction) with very high In mole fraction.
The Band-Gap Studies of Short-Period CdO/MgO Superlattices