Raman Studies of InGaAlAs Digital Alloys

Abstract

Optical phonons in InGaAlAs digital alloy structures are systematically studied in terms of (In0.53Ga0.47As)(l)/(In0.52Al0.48As)(l) (period length l = 1, 2, 4, 5) and (In0.53Ga0.47As)(1-z)/(In0.52Al0.48As)(z) (composition z = 0.2, 0.4, 0.6, 0.8) short-period superlattices. Raman spectra reveal GaAs-like and AlAs-like longitudinal optical (LO) phonons confined in In0.53Ga0.47As and In0.52Al0.48As layers, respectively. In As-like LO phonons are also observed in the In0.53Ga0.47As and the In0.52Al0.48As layers. The confined GaAs-like LO phonon frequency is sensitive to the In0.53Ga0.47As layer thickness and shifts downward by similar to 7 cm(-1) with decreasing layer thickness, showing excellent agreement with the LO phonon dispersion for bulk GaAs. Importantly, the confined Al As-like LO phonon frequency is not sensitive to the In0.52Al0.48As layer thickness, indicating the presence of high-quality interface boundaries between the In0.53Ga0.47As and the In0.52Al0.48As layers.