ABSTRACT
We present results of a detailed far-infrared magneto-optical study on a series of high-mobility InAs/Al x Ga1- x Sb (0.1 ≤ x ≤ 1.0) type-II single quantum wells. Semiconducting samples (x ≥ 0.4), in which only 2D electrons exist in the InAs wells, exhibited cyclotron resonance (CR) splittings due to large nonparabolicity. Semimetailic samples (x = 0.2 and 0.1), in which both 2D electrons and 2D holes are present, showed a variety of absorption lines, including "X-lines” that we have ascribed to intra-exciton transitions and electron-CR with strongly oscillatory linewidth, amplitude, and mass, part of which are interpreted in light of peculiar "anti-nonparabolic" band structure resulting from band overlap and coupling between conduction-band states in InAs and valence-band states in AlGaSb.
