Book excerpt: The elastic constant (EC) is a very important mechanical property of the these materials and its significance is already well known in literature. This first monograph solely deals with the quantum effects in EC of heavily doped (HD) low dimensional materials. The materials considered are HD quantum confined nonlinear optical, III-V, II-VI, IV-VI, GaP, Ge, PtSb₂, stressed materials, GaSb, Te, II-V, Bi₂Te₃, lead germanium telluride, zinc and cadmium diphosphides, and quantum confined III-V, II-VI, IV-VI, and HgTe/CdTe super-lattices with graded interfaces and effective mass super-lattices. The presence of intense light waves in optoelectronics and strong electric field in nano-devices changes the band structure of semiconductors in fundamental ways, which have also been incorporated in the study of EC in HD low dimensional optoelectronic compounds that control the studies of the HD quantum effect devices under strong fields. The importance of measurement of band gap in optoelectronic materials under intense external fields has also been discussed in this context. The influences of magnetic quantization, crossed electric and quantizing fields, electric field and light waves on the EC in HD semiconductors and super-lattices are discussed.The content of this book finds twenty-five different applications in the arena of nano-science and nano-technology. We The authors have discussed the experimental methods of determining the Einstein Relation, screening length and EC in this context. This book contains circa 200 open research problems which form the integral part of the text and are useful for both PhD aspirants and researchers in the fields of condensed matter physics, materials science, solid state sciences, nano-science and technology and allied fields in addition to the graduate courses in semiconductor nanostructures.