Multiple quantum well (MQW) materials composed of Pb0.81Sn0.19Se wells and Pb0.80Sr0.20Se barriers with intersubband energy gaps of 343 meV and 450 meV were modeled for thermophotovoltaic (TPV) device performance. The effect of L-valley degeneracy removal in these (111)-oriented IV-VI semiconductor quantum wells was evaluated. Degeneracy splitting reduces the effective densities of states in both the valence and conduction bands. Thermally generated intrinsic charge carrier concentrations are smaller by a factor of three as compared to bulk materials with the same bandgap energies. A current-matched dual junction TPV cell made from these MQW materials in a generator with a 1215°C radiator is predicted to have a power density of 2.34 W/cm2, 49% better than the power density generated by a cell made from bulk materials with the same bandgap energies.

In this work, a theoretical model is used to study the gain versus current-density relationship for IV-VI semiconductor quantum well lasers. The model, based on Kane's two band theory, solves for the anisotropy in the constant energy surfaces and for the strong nonparabolicity of the bands. The system investigated is the EuSe-PbSeo,7sTeo,22 q uantum well structure at 77 K. The effects of nonparabolicity on the gain versus current-density relation are a reduction in the current density needed for any given gain and an increase in the gain saturation level. The nonparabolicity of the bands in the growth direction lowers the values of the confinement factor relative to parabolic bands which in turn lowers the modal gain values. Finally, the effects of nonparabolicity on the threshold current are significant for short cavity lasers and decrease with an increase in the cavity length. 0 I995 American Institute of Physics.

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The aim of this study was to analyse student responses to the introduction of flipped learning methodology at an institution of higher education in the northern region of the United Arab Emirates to identify potential relationships between and among the responses and to determine underlying factors guiding the responses. A survey questionnaire was developed by a team of faculty and sent to students via online survey software. The analysis employed dimension reduction techniques to ascertain underlying factors guiding responses. Two major factors were identified: (1) the focus on educational benefits of the methodology and (2) the instructional relevance of the flipped classroom approach. The study concluded that flipped learning methodology can be useful for improving learning and holds the potential to more adequately engage today's learners.