S, Manjula

English

Open Access Repository of Indian Theses

Abstract/Synopsis              Following the pioneering work of Lee Esaki and Tsu in 1970 on thestudy of two dimensional semiconducting heterostructures like Quantum Well,superlattices etc., and the developments in the ultrathin film growth techniquesusing Molecular Beam Epitaxy, Metal Organic Vapour Phase Epitaxy, the topicof Low Dimensional Semiconducting Systems(LDSS) like Quantum Well,Quantum Well Wire and Quantum Dot has developed rapidly both from thepoint of view of basic Physics and of applications. Consequence of the one –dimensional, two – dimensional and three dimensional size quantization, agenuine quantum mechanical effect, the degrees of freedom is frozen and thecarriers in such LDSS effectively behave as if their motion were twodimensional, one dimensional and zero dimensional, a feature which alters anumber of physical properties. Also a wide variety of quantum heterostructuredevices have come into vogue because of the dramatic development inSemiconductor materials and technology. In the present thesis, some aspects ofLDSS like the influence of external perturbations like temperature and pressureon the ground state as well as some low lying excited states, diamagneticsusceptibility of a donor in ground state as well as in the low lying excitedstates, the effect of external pressure on diamagnetic susceptibility and Metal –Insulator transition have been investigated and are presented in six chapters(from chapter 2 to chapter 7).The temperature dependent binding energy of some low lying excited states for a compositional Quantum Well have been calculated for various impurity locations by extending the investigation of Elabsy.4 It has been observed that the temperature plays an important role in the binding energy of low lying excited states also.Bottom of FormTop of FormBottom of FormThe effect of Γ-X crossover due to the external hydrostatic pressure on the ground state donor binding energy as well as for some low lying excited states for a Quantum well has been investigated by considering the non-parabolicity of the conduction band and pressure dependent spatial dielectric screening. It is observed that the effect of Γ-X crossover is predominant for ground state than for low lying excited statesThe binding energies of a hydrogenic donor both in the parabolic and non-parabolic conduction band model within the effective mass approximation have been computed for the low-dimensional semiconducting systems (LDSS) like quantum well, quantum well wire and quantum dot taking GaAs/AlxGa1−xAs systems as an example. It is observed that the effect of non-parabolicity is not effective when the system goes to lower dimensionality. The diamagnetic susceptibility of a hydrogenic donor impurity has also been computed in these LDSS in the infinite barrier model. Since no theoretical or experimental works on the diamagnetic susceptibility of LDSS are available in the literature, as a realistic case the diamagnetic susceptibility has been computed in the finite barrier model (x=0.3) for a quantum well and the results are discussed in the light of semiconductor–metal transition.We present the calculation of diamagnetic susceptibility (χdia) of a hydrogenic donor in GaAs/AlxGa1−xAs quantum well for various compositions of Al and for different impurity locations within the well. The effect of Γ–X band crossing due to hydrostatic pressure on χdia is also investigated taking into account the non-parabolicity of the conduction band.

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Open Access Repository of Indian Theses