http://hdl.handle.net/10311/66 2026-07-11T06:36:12Z 2026-07-11T06:36:12Z Tshipa, Moletlanyi Sharma, Lalit K. Pratap, Surender http://hdl.handle.net/10311/2531 2023-12-09T00:24:27Z 2021-06-22T00:00:00Z

Photoionization cross-section in a GaAs spherical quantum shell: the effect of parabolic confining electric potentials Tshipa, Moletlanyi; Sharma, Lalit K.; Pratap, Surender Theoretical study on binding energies due to a centred charged impurity and the associated photoionization cross-section (PCS) in a spherical shell are presented. This was achieved by solving the Schrödinger equation within the effective mass approach. Intrinsic to the spherical quantum shell may be the parabolic potential or the shifted parabolic potential, each superimposed on an infinite spherical square well. Results indicate that the parabolic potential enhances binding energies while the shifted parabolic potential diminishes them. These electric potentials considerably modify photoionization cross section in two ways. One, the parabolic potential blueshifts peaks of PCS while the shifted parabolic potential redshifts the peaks. Second, the parabolic potential decreases the magnitude of the peaks of the PCS while the shifted parabolic potential increases the magnitudes of the peaks. In essence, these two potential may be used to manipulate PCS in quantum structures.

2021-06-22T00:00:00Z Tshipa, Moletlanyi http://hdl.handle.net/10311/2530 2023-12-09T00:17:26Z 2019-07-10T00:00:00Z

Optical properties of GaAs nanowires with an electric potential that varies inversely with the square of the radial distance Tshipa, Moletlanyi A theoretical investigation of optical properties of a cylindrical quantum wire (CQW) is presented. The properties studied were optical absorption coefficient (AC) and change in refractive index (CRI) of the quantum wire. In particular, effect of an inverse parabolic potential on the optical properties of CQWs was investigated. This was done by solving the Schrödinger equation within the effective mass approximation to obtain the wave functions. The inverse parabolic potential reduces transition energies and therefore redshifts peaks of the AC, as well as the anomalous dispersion region of the dependence of change in refractive index on the photon energy. The inverse parabolic potential also has effect on the magnitudes of these optical quantities, reducing the AC and enhancing the CRI. These properties of the inverse parabolic confining electric potential can have a wide range of applications in nanodevice technology, some details of which are discussed.

2019-07-10T00:00:00Z Tshipa, Moletlanyi http://hdl.handle.net/10311/2529 2023-12-09T00:11:52Z 2019-01-01T00:00:00Z

Effect of an inverse parabolic confining electric potential on third harmonic generation in cylindrical quantum wires Tshipa, Moletlanyi A theoretical investigation of the effect of an inverse parabolic potential on third harmonic generation in cylindrical quantum wires is presented. The wave functions are obtained as solutions to Schrödinger equation solved within the effective mass approximation. It turns out that peaks of the third harmonic generation susceptibility (THGS) associated with nanowires of small radii occur at larger photon energies as compared to those associated with quantum wires of larger radii. The inverse parabolic potential red-shifts peaks of the THGS, and suppresses the amplitude of the THGS. THGS associated with higher radial quantum numbers is diminished in magnitude and blue-shifted, as a function of the photon energy. As a function of the inverse parabolic potential, the THGS still characterized by peaks, and the peaks shift to lower values of the potential as the photon energy increases.

2019-01-01T00:00:00Z Tshipa, Moletlanyi http://hdl.handle.net/10311/2528 2023-12-09T00:00:15Z 2023-08-07T00:00:00Z

Probing semiconductor quantum well qubits and associated Shannon entropy using semi‑relativistic quantum mechanics Tshipa, Moletlanyi Electron states in GaAs, GaN and AlN quantum wells are studied by solving a semi-relativistic wave equation within the effective mass approximation. The quantum states are in turn used to probe the properties of two-level qubits formed in the different quantum wells at various temperatures. Results indicated that the period of oscillation between the quantum states increases with increasing width of the quantum wells, with AlN having the longest period and shortest for GaAs. Transition rates were also studied, since their product with the period of oscillation yield important information concerning the feasibility of carrying out a quantum computation. This product is equivalent to the ratio of the period of oscillation between states to the lifetime of an electron in an excited state. From the results, GaAs quantum wells may be preferable as they have the lowest ratio compared with the other quantum wells of other materials. AlN has the highest ratio of the three semiconductors considered here. Shannon entropy in the different quantum wells was studied also. It was found that the entropy in GaAs quantum wells varies rapidly through the passage of time, while those of GaN and AlN vary relatively slowly. NB: Some symbols may not appear as they are on the original document.

2023-08-07T00:00:00Z