OPTICAL STUDIES OF STRAINED PSEUDOMORPHIC SEMICONDUCTOR HETEROSTRUCTURES UNDER EXTERNAL-PRESSURE

Epilayers and quantum well heterostructures of group III-V and II-VI b inary and ternary compounds offer an exciting array of band gaps and p hysical properties. The band gaps range from the infrared to the near ultraviolet region (0.1 to 3 eV); continuous tuning of the band gap is achieved by means of alloying, strain and quantum confinement. Pseudo morphic heterostructures with large lattice mismatch and minimal dislo cations and defects at the interface have been successfully grown by v arious techniques. This paper reviews the effects of strain on the opt ical and electronic properties, determination of strain, tuning of str ain, and the structural stability of these metastable structures. Phot oreflectance, photoluminescence and Raman scattering studies as a func tion of temperature and externally applied hydrostatic pressure are di scussed. Owing to the different compressibilities and thermal expansio n coefficients of the constituent members of a heterostructure, the st rain can be continuously tuned by these perturbations. Depending on th e relative signs of the lattice mismatch strain and the pressure (or t emperature) induced strain, the net strain in the structure could incr ease or decrease. Examples of both cases are presented.