In Ge∕Si Stranski-Krastanov nanostructures grown by chemical vapor deposition, the authors find ∼30meV/decade photoluminescence (PL) spectral shift toward greater photon energies as excitation intensity increases from 0.1to104W∕cm2. The PL lifetime exhibits strong spectral dependence, and it decreases from ∼20μs at 0.77eVto200ns at 0.89eV. The authros attribute the observed PL spectral shift and shorter PL lifetime at higher photon energies to an increasing contribution from recombination between holes populating excited Ge cluster energy states and electrons in SiGe alloy cluster regions.

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Three-dimensional SiGe nanostructures grown on Si (SiGe/Si) using molecular beam epitaxy or low-pressure chemical vapor deposition exhibit photoluminescence and electroluminescence in the important spectral range of 1.3–1.6 μm. At a high level of photoexcitation or carrier injection, thermal quenching of the luminescence intensity is suppressed and the previously confirmed type-II energy band alignment at Si/SiGe cluster heterointerfaces no longer controls radiative carrier recombination. Instead, a recently proposed dynamic type-I energy band alignment is found to be responsible for the strong decrease in carrier radiative lifetime and further increase in the luminescence quantum efficiency.

IntroductionFor the past 40 years, crystalline Si (c-Si) continues to be the major material for microelectronics, and modern silicon technology is superior compared to other semiconductors (e.g., II-VI and III-V compounds). In addition to the unique electronic and structural properties of bulk c-Si, silicon dioxide (SiO 2 ) and Si/SiO 2 interfaces, single-crystal Si possesses one of the best known lattice thermal conductivity [1,2]. This exceptional heat conductance is critically important for Si device heat management and circuit reliability. However, most of the modern complementary metal-oxide-semiconductor (CMOS) platforms are no longer single-crystal Si wafers but rather thin layers of Si-on-insulator (SOI), ultrathin strained Si and SiGe heterostructures that are the foundation of SiGe bipolar transistors (HBTs), and high-mobility metal-oxide-semiconductor field-effective transistors (MOSFETs). Major properties of these Si-based nanostructures are very different from those of bulk c-Si. For example, thermal conductivity in ultrathin SOI layers, SiGe alloys, and Si/SiGe nanostructures could be reduced by more than an order of magnitude compared to that in c-Si [3-6], and heat dissipation has become an important issue for modern nanoscale electronic devices and circuits. Thus, the understanding and improvement of heat management in Si-based nanostructures is critically important for the evolution of microelectronic industry.On the other hand, many interesting applications of nanostructured Si (ns-Si) in photonic devices and CMOS-compatible light emitters were recently discussed [7][8][9][10][11]. These ns-Si materials and devices can be produced by electrochemical anodization (i.e., porous Si [12]), chemical vapor deposition (CVD) using thermal decomposition of SiH 4 [13-15], Si ion implantation into a SiO 2 matrix [16], and deposition of amorphous Si/SiO 2 layers followed by thermal crystallization [17][18][19]. These ns-Si materials and devices produce an efficient and tunable light emission in the near-infrared and visible spectral region [20,21]. Also, it has been shown that under photoexcitation with energy density >10 mJ/cm 2 , optical gain is possibly Silicon Nanocrystals: Fundamentals, Synthesis and Applications. Edited by Lorenzo Pavesi and Rasit Turan