09:45 〜 10:00
▼ [16a-3A-4] Interference effects on transmission magnetic circular dichroism spectra of GaMnAs
キーワード：GaMnAs,MCD,ferromagnetic semiconductor
Recent studies of GaMnAs have revealed that ferromagnetic and transport properties of GaMnAs are dominated by holes in the impurity band which is formed near the top of the valence band. To investigate the spin-dependent impurity band structures, transmission magnetic circular dichroism (MCD) spectroscopy has been widely studied. In the previous studies, the band structure of GaMnAs was mainly discussed by the spectral shape of transmission MCD at around the photon energy E = ~1.5 eV where optical transitions from the impurity band to the conduction band are expected to be detected. Meanwhile, one must be careful when interpreting the magneto-optical (MO) spectra, because they can be influenced by optical interference effects. Also, there is a large background in transmission MCD spectra of GaMnAs, which makes the interpretation of the MCD spectra difficult especially near the Γ-critical point. Recently, we succeeded in deriving the off-diagonal element of the dielectric tensor of GaMnAs, which is intrinsic to the material and which can express the MO effects, from systematic reflection MCD measurements. In this study, we calculated the transmission MCD spectra by considering the interference effects and found that transmission MCD spectra are strongly influenced by interference even in films as thin as 50 nm, although the thicknesses d of the GaMnAs films were 50-300 nm in the previous studies. When E < 2.5 eV, the peak (or dip) positions and even the spectral shape of MCD vary with d. We note that the d dependence of MCD is negligibly small when E > 2.75 eV due to the large extinction coefficient of GaMnAs. This result means that we must be very careful when we discuss the band structure by raw transmission MCD spectra at E < 2.5 eV.