The device performance of GaAs p-i-n solar cells containing stacked layers of self-assembled InAs quantum dots is investigated. The solar cells demonstrate enhanced external quantum efficiency below the GaAs band gap relative to a control device without quantum dots. This is attributed to the capture of sub-band gap photons by the quantum dots. Analysis of the current density versus voltage characteristic for the quantum dot solar cell reveals a decrease in the series resistance as the device area is reduce from 0.16 cm2 to 0.01 cm2. This is effect is not observed in control devices and is quantum dot related. Furthermore, low temperature measurements of the open circuit voltage for both quantum dot and control devices provide experimental verification of the conditions required to realise an intermediate band gap solar cell.

Solar cells based on InAs quantum dots embedded in InxGa1-xAs quantum wells grown on n-type GaAs substrate were fabricated and tested. Solar cells with In mole fraction (x) in the range of 0-40% were investigated. The performance of the solar cells was evaluated using current-voltage characteristics, spectral response, and quantum efficiency measurements. The spectral response and quantum efficiency spectra possess several peaks along the lower energy side of the spectra, which are attributed to the interband transitions in the structure. These peaks are red shifted as x is increased above 0 %. The device power conversion efficiency was extracted from the current-voltage characteristics using an AM 1.5 solar simulator. The short circuit current density increased as the x is increased above 0 %. But the overall power conversion efficiency decreased due to decrease in the open circuit voltage. The decrease in open circuit voltage is due strain induced dislocations caused by lattice mismatch.

Quantum dot gate (QDG) field-effect transistors (FET) have shown three-state transfer characteristics. Quantum dot channel (QDC) field-effect transistors (FET) have exhibited fourstate ID-VG characteristics. This project aims at studying the effect of incorporating cladded quantum dot layers in the gate region of QDC-FET. Four-state characteristics are explained by carrier transport in narrow energy mini-bands which are manifested in a quantum dot superlattice (QDSL) channel. QDSL is formed by an array of cladded quantum dots (such as SiOx-Si and GeOx-Ge). Multi-state FETs are needed in multi-valued logic (MVL) that can reduce the number of gates and transistors in digital circuits. The fabricated device showed the four-state characteristic (OFF, ‘I1’, ‘I2’, ON).

A study on light absorption enhancement of an InAs quantum dots embedded into InxGa1-xAs quantum well with GaAs as a barrier solar cells was carried out. Solar cell devices were fabricated from different structures, which were grown by using molecular beam epitaxy, with the In mole fraction (x) varied between 0 – 25 %. Poly-L-Lysine ligands and ZnO sol-gel was used to modify the surface of the solar cells and act as anti-reflection coatings. The anti-reflection characteristic of the ligands and the sol-gel were investigated by measuring the solar cell characteristics before and after the solar cells surface modifications. The current-voltage characteristics were measured of the fabricated solar cells before and after Poly-L-Lysine and ZnO coatings. A significant enhancement on the order of 40 % of the solar cells performance was observed. This type of enhancement was observed in the power conversion efficiency, spectral response measurements, and external quantum efficiency.