Strain relaxation, band-structure deformation, and optical absorption in free-hanging quantum-well microstructures

Abstract

We have measured changes to the band structure due to strain relaxation in micromachined multiple quantum-well microstructures that are released from the substrate. Analytic expressions for the strain tensor in the free-hanging heterostructure are presented and used in an eight-band k∙p model to predict the changes to the band structure in the micromachined heterostructure. The deformed band structure is measured optically using spatially resolved differential transmission spectroscopy and found to be in excellent agreement with predictions. The measurements indicate (i) that strained semiconductor heterostructures relax elastically upon release from the substrate, (ii) that k∙p theory combined with our strain relaxation expressions accurately model the optical properties of micromachined heterostructures, and (iii) that a significant asymmetry exists between the effects of compressive and tensile strains on optical absorption in these microstructures. Our results show that micromachining represents an important tool to modify the optical properties of quantum-well heterostructures.