Superlattices optical absorption

Oonishi, T., Sato, S., Yao, H. and Kimura, K. (2007) Three-dimensional gold nanopartide superlattices Structures and optical absorption characteristics. Journal of Applied Physics, 101, 114314. 

Nanocomposites in the form of superlattice structures have been fabricated with metallic, " semiconductor,and ceramic materials " " for semiconductor-based devices. " The material is abruptly modulated with respect to composition and/or structure. Semiconductor superlattice devices are usually multiple quantum structures, in which nanometer-scale layers of a lower band gap material such as GaAs are sandwiched between layers of a larger band gap material such as GaAlAs. " Quantum effects such as enhanced carrier mobility (two-dimensional electron gas) and bound states in the optical absorption spectrum, and nonlinear optical effects, such as intensity-dependent refractive indices, have been observed in nanomodulated semiconductor multiple quantum wells. " Examples of devices based on these structures include fast optical switches, high electron mobility transistors, and quantum well lasers. " Room-temperature electrochemical... 

This chapter concentrates on the design of efficient dipolar NLO chromophores and the different approaches for their incorporation in non-centrosymmetric materials, including guest-host polymer systems, chromophore-functionalized polymers (side-chain and main-chain), cross-linked chromophore-macromolecule matrices, dendrimers, and intrinsically acentric self-assembled chromophoric superlattices. The different architectures will be compared together with the requirements (e.g., large EO coefficient, low optical absorption, high stability, and processability) for their incorporation into practical EO devices. First, a brief introduction to nonlinear optics is presented. 

In this chapter we review the work done in our laboratory on the structure (Part II), optical absorption (Part III), photoluminescence (Part IV), and electrical transport (Part V) of a-Si H/a-SiNjci H superlattices. Results with single quantum well structures are discussed by Kukimoto in Chapter 12 of Volume 2ID. 

Optical absorption has been studied in superlattices made of a-Si H layers alternating with a-SiN iH, a-Si, tQ H, or a-Ge H (Abeles and Tiedje, 1983 Tiedje et al., 1984). Figure 4 shows the optical absorption coefficienta versus photon energy of a series of a-Si H/a-SiN H superlattices about 1 fiia thick, in which the thickness of the a-Si H layer Ls is varied and the a-SiN , H layer thickness 35 A is held fixed. The large blue shift in the optical absorption edge with decreasing has been attributed to an increase... 

Fig. 6. Optical absorption coefficient a for the a-Si H/a-SiN H superlattice for values of wbll width Lg = 400,20, and 8 A plotted as (otE) versus photon energy E. The experimental data aregivenby the full circles. The solid curves were calculated for the density-of-states model shown in Fig. Sb. The extrapolation of the gap E, is shown for the case of 1. — 20 A by the dashed line. (From Tiedje et al. (1984).]...

Fig. 14. Optical absorption coefficient a determined from photoconductivity for a-Si H/ a-SiNjj H superlattice film 1.2 /im thick with alternating layers of 1200 A a-Si H and 35 A...

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