Strain Effect in Large Silicon Nanocrystal Quantum Dots

The strong quantum confinement of carriers exhibited in Si nanocrystals (nc-Si) embedded in SiO₂ has shown great potential for novel ultrasmall electronic logic and memory devices. Several different self-assembling process techniques, usually those involving low-pressure chemical vapor deposition and oxidation, ^{1 , 2} are expected to generate strain at the Si/SiO₂ interface, resulting in different nc-Si geometries. Although much experimental and theoretical work has been devoted to investigating strain due to bond density mismatch and stress buildup from thermal expansion behavior at planar Si/SiO₂ interfaces, theoretical analyses of strain effects of nc-Si have been relatively scarce. ³ Recently, high resolution 836transmission electron microscopy and X-ray analysis of nc-Si in Si/SiO₂ superlattices have revealed that inhomogeneous strain in nc-Si can range from 0.1% to 3.25%, depending on the crystal size and the process annealing temperature. ⁴ These effects are sufficiently important to significantly influence the electronic properties of nc-Si with profound consequences for quantum-device application.