Nanocrystalline Semiconductor Films and Size Quantization

To facilitate a self-contained description, we will start with well-established aspects related to the semiconductor energy band model and the electrostatics at semiconductor electrolyte interfaces in the dark . We shall then examine the processes of light absorption, electron-hole generation and charge separation at these interfaces. Finally, the steady-state and dynamic (i.e., transient or periodic) aspects of charge transfer will be considered. Nanocrystalline semiconductor films and size quantization are briefly discussed, as are issues related to electron transfer across chemically modified semiconductor electrolyte interfaces. 

Finally, the tendency for CD films to be nanocrystalline and often to exhibit quantum-size effects is treated in the final chapter, Chapter 10, Nanocrystallinity and Size Quantization in CD Semiconductor Films. 

The layout of this book means that there will be some overlap between sections. However, this system should allow those readers interested in one or more specific sections to skip the others, thereby making the book more efficient for the individual reader. An example of this is the use of quantum-size effects to elucidate CD mechanisms. This is treated, with different emphasis, both in Chapter 3 (Mechanisms of Chemical Deposition) and in Chapter 10 (Nanocrystallinity and Size Quantization in CD Semiconductor Films). 

Nanocrystallinity and Size Quantization in Chemical Deposited Semiconductor Films... 

A colloid chemical approach to CdS/HgS/CdS spherical quantum wells was described [79]. Size-dependent third-order non-linear susceptibilities of CdS clusters were investigated [80]. Reviews appeared on size-quantized nanocrystalline semiconductor films [81] and on the quantum size effects and electronic properties of semiconductor microcrystallites [82]. 

Nanocrystalline particulate films, which exhibit pronounced quantum size effects in three dimensions, are of great interest due to applications in solar cell (108-112) and sensor (57, 113-115) applications. They exhibit novel properties due to not only the SQE manifested by individual nanoparticles but also the total surface area. Unlike MBE and MOCVD methods used to prepare quantum well electrodes, these electrodes can be prepared by conventional chemical routes described in Section 9.5.2.2. For example, II-VI semiconductor particulate films were prepared by using low concentrations of precursors and by controlling the temperature of the deposition bath. Nodes demonstrated the SQE for CdSe thin films deposited by an electroless method (98). The blue shift in the spectra of CdSe films has been demonstrated to be a function of bath temperature. As described in Section 9.5.2.1, electrodeposition of semiconductors in non-aqueous solvents leads to the formation of size-quantized semiconductor particles. On a single-crystal substrate, electrodeposition methods result in epitaxial growth (116, 117), and danonstrate quantum well properties. 

---