Quantum control, semiconductor

Calculating the exact response of a semiconductor heterostructure to an ultrafast laser pulse poses a daunting challenge. Fortunately, several approximate methods have been developed that encompass most of the dominant physical effects. In this work a model Hamiltonian approach is adopted to make contact with previous advances in quantum control theory. This method can be systematically improved to obtain agreement with existing experimental results. One of the main goals of this research is to evaluate the validity of the model, and to discover the conditions under which it can be reliably applied. 

An interesting development in this field is the recent report by Dameron et al. (88) of the biosynthesis of quantum-sized CdS crystals in the yeast cells Candida glabrata and Schizo saccharomyces pombe. Exposed to Cd ions these cells synthesize certain peptides with an enhanced sulfide production. Small CdS crystals are formed inside the cells. These crystallize in the rock salt structure (and not in the thermodynamically stable hexagonal configuration). The organism controls particle nucleation and growth, so that uniformly sized CdS particles of about 20 A are formed. They show pronounced quantum-size effects. This is the first example of the biosynthesis of quantum-sized semiconductor crystallites. It constitutes a metabolic route for the detoxification of Cd " -infected living cells (see also 89). 

We note that zeolites have also been used as hosts for a number of other intriguing "nanocomposites", for example in the field of encapsulated quantum-size semiconductor particles such as Se, CdS, CdSe, PbS, and GaP.3h32,33,34,35 phe encapsulation of metals such as Bi, Hg, Sn and Ga in zeolites has been described by Bogolomov.36 These studies demonstrate the enormous versatility of zeolite host systems for studies and control of structural/electronic relationships. 

Doped superlattices are proper for controllable semiconductor components. They are compatible with dense optical and electronic integration and could provide required performance characteristics of the devices. Unique features of the doped superlattices, or n-i-p-i crystals, are spatial separation of electrons and holes, tunable energy band gap, increased current carrier lifetime, wide variation of the potential profile and changing the electric and optical characteristics versus design parameters or added quantum wells and 6-doped layers [1,2],... 

Recently, much attention has been paid to the importance of the quantum function realized by micro- and mesoscopically controlled semiconductor heterostructures. Conducting polymer heterolayers, leading to a conducting polymer superlattice exhibiting quantum size effects, should take an important place in both novel electronic and optical devices. 

M. W. FLeming and A. Mooradlan, "Spectral Characteristics of External-cavity Controlled Semiconductor Lasers", IEEE J. Quantum Electron., QE-17. 44 (1981). 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

Tang, J. and Marcus, R. A. (2005) Diffusion-controlled electron transfer processes and power-law statistics of fluorescence intermittency of nanoparticles. Phys. Rev. Lett, 95, 107401-1-107401-4 Tang, J. and Marcus, R. A. (2005) Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots./. Chem. Phys., 123,054704-1-054704-12. 

Particle size and the method of nanoparticle preparation (including the capping agent used) determine the physical and electronic properties of the quantum dots produced. This gives chemists the unique ability to change the electronic and chemical properties of a semiconductor material by simply controlling particle size and preparative conditions employed. There are various methods for the preparation of nanoparticles however, not all methods work well for the preparation of compound semiconductor nanocrystallites. 

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