Novel narrow-gap semiconductor systems

Abstract

The development of new epitaxial techniques has given rise to a variety of novel material combinations. Pseudomorphic combinations where the partners have lattice constants which differ by more than 1 are currently being extensively studied. The built-in strain can alter the symmetry and magnitudes of the band gaps concerned. Interesting examples of systems currently being investigated are strained layer superlattices based on Si/Si ixGex GiAs/lnAs and InSb/InSb ixA5x. The growth and properties of narrow gap semiconductor systems are reviewed together with their use as components for strained layer structures. The materials discussed are InSb InAs the alloys of these two compounds and alpha tin. The alloy system InAsiSb is prone to metallurgical problems such as ordering and phase separation in the mid alloy range but high mobility samples have been grown. Other alloy systems are also affected by similar problems. The strain associated with the small but significant mismatch between alpha-tin and InSb stabilises the alpha phase up to 100C and opens up an energy gap of 0. 2eV. The first observation of the Shubnikovde Haas effect with this heterostructure system demonstrates the presence of a high density twodimensional electron gas at the interface. The carrier density is too high to arise solely from the band offsets. Spike-doped and n-i-p-i structures are studied in InSb and InAs. Minimal dopant diffusion is found and highly non-linear optical absorption and a striking Quantum