Optical Gain Properties of Serpentine Superlattice Quantum Wire Arrays,

Quantum confinement in two dimensions, which results in quantum wires is likely to result in improved device characteristics due to density of states localization and anisotropic optical properties. However, to observe significant quantum wire effects at room temperature, the carriers should be confined to less than 100 angstrom in two dimensions, which is too difficult to fabricate even with the finest lithographic techniques developed so far. However, another fabrication technique which holds great promise is the direct growth of lateral superlattices on vicinal substrates. On the surfaces of such substrates uniform atomic steps are formed under proper conditions. The lateral superlattices are directly grown on such surfaces by the sequential deposition of two materials of different compositions. The end result is an array of quantum wires QWR with a period, T. The period is solely determined by the substrate tilt angle, alpha, and monolayer thickness, d, which is expressed as T d tan alpha. For example, when alpha is 2 deg, T becomes 81 angstrom, and when alpha is 1.5 deg, T becomes 108 angstrom in AlGaAs system. Amongst these lateral superlattices, a curved interfaced lateral superlattice named serpentine superlattice SSL has been developed to decrease the sensitivity of the fabricated structure to growth conditions and improve its uniformity. This makes SSL more desirable compared to tilted superlattices TSL which have rectangular cross sectional geometry.