Theoretical Study of Optical Properties of III-V Compound Semiconductor Quantum Well Structures

[[abstract]]In the paper, the optical properties of III-V compound semiconductor quantum well structures are studied theoretically. The authors take into account the nonparabolic valence band structure due to band mixing effect using multiband effective mass theory (k.p theory). A variational method is used to solve the exciton problem. The calculated exciton peak positions versus electric field show good agreement with other published experimental results. The optical absorption coefficient and spontaneous emission rate in quantum well structures are calculated using the formula derived by the density matrix formalism with intraband relaxation taken into account. The optical gain and refractive index variation in a quantum well laser structure are calculated by giving equal electron and hole density in the well region. The theoretical results show that the peak position of the gain spectra exhibits a red shift and its amplitude decreases with increasing electric field for both the TE and TM polarization. The gain spectra in the model shows remarkable difference both in the spectra shape and the peak amplitude as compared with those from the conventional models. The peak gain is reduced and the gain spectrum is more symmetric and closer to experimental observations. The refractive index variation in the active region results in the defocusing effect and increase of optical losses[[fileno]]2030170030045[[department]]電機工程學

From semiclassical transport to quantum Hall effect under low-field Landau quantization

The crossover from the semiclassical transport to quantum Hall effect is studied by examining a two-dimensional electron system in an AlGaAs/GaAs heterostructure. By probing the magneto-oscillations, it is shown that the semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the minima of the longitudinal resistivity approach zero. The extension of the applicable range of the SdH theory could be due to the damping effects resulting from disorder and temperature. Moreover, we observed plateau-plateau transition like behavior with such an extension. From our study, it is important to include the positive magnetoresistance to refine the SdH theory.Comment: 11 pages, 5 figure

Origin of Photoluminescence in Hydrogenated Amorphous Silicon-rich Nitride and Oxynitride Thin Films

[[fileno]]2030170010164[[department]]電機工程學

Effect of Annealing of Epitaxial Ge Overlayers on Si(001) Surface Studied by LEED and AES

[[fileno]]2030170030146[[department]]電機工程學

Theoretical Study of Optical Properties of III-VI Compound Semiconductor Quantum Well Structures

[[fileno]]2030170030119[[department]]電機工程學

Mechanical properties and deformation behavior of amorphous nickel-phosphorous films measured by nanoindentation test

In this study, amorphous Ni-P films were deposited by electroless plating under different pH values. Their mechanical properties and deformation behavior were then investigated by instrumented nanoindentation. With increasing pH value of the plating solution from 3.75 to 6.0, the hardness and elastic modulus of the obtained Ni-P films increased from 6.1 GPa and 146 GPa to 8.2 GPa and 168 GPa respectively. From the load-indentation depth curve, the Ni-P films were found to yield at an indentation depth of 8 nm. By microstructural examination around the indented regions, early-stage plastic deformation of the amorphous Ni-P films was verified through the formation and extension of shear bands with a spacing of several tens of nanometers. Within the shear bands, flow dilatationinduced intense shear localization was expected and resulted in crystallization in the amorphous matrix. The critical shear stress and energy release rate required for the initiation of early-stage plastic yielding of the Ni-P films were calculated to be about 1.4 GPa and 3.0 J/m(2) respectively, both of which increased with pH values

On Classifying Discussion Threads Using Travel Information Goal-Oriented Model

We study how to recommend discussion threads in the tourism domain to meet visitors’ travel information needs. This research-in-progress paper reports the first stage of our research, namely classifying discussion threads into travel goals. We propose an information goal-oriented model, which consists of four goals: Initiation, Attraction, Accommodation, and Route planning, that can be characterized using nine features. Seven of these nine features can be quantified based on lexicons, and the other two can be measured using the named entity recognition technique. Three lexicons can be further enhanced using WordNet. We conduct an experiment in evaluating the impact of these features on goal classification with a data set collected from TripAdvisor.com, the world\u27s largest travelling website. The experimental results show that our approach generally has comparable or better performance than that of using purely lexical features, namely TF-IDF, for classification

Effect of Streptococcus mutans on mechanical properties of human dental structures

In this Study, the mechanical properties of human dental structures have been investigated by using instrumented nanoindentation. Immersion in solutions containing Streptococcus mutans, which is the principal cause of dental caries, was applied to tooth specimens to clarify its effect oil the microstructure and mechanical properties of the dental Structures. With in extended time of up to 16 h, the pH value of the S. mutans Solutions dropped front 7.3 to 5.8. Therefore, after immersion in the S. mutans solutions for 16 h. slight erosions of the dental structures began, after 64 It, severe tooth decay Occurred with obviously etched dental features. After 129 h. the elastic modulus of enamel and dentine dropped to 85 and 67%, respectively, of the original Values Of untreated specimens, and the hardness dropped to 88 and 55%, respectively