| Summary: | 碩士 === 國立臺南大學 === 材料科學系碩士班 === 103 === There are two parts in this research. The first part is the study of effects of Mn content in Cd1-xMnxTe grown by molecular beam epitaxy (MBE) on silicon (Si) (111) substrate. Owing to different binding energy of atoms, Te-Te binding shows the lower forming energy than Cd-Te, results in the production of Te-Te binding defects. Incorporation of Mn atoms into CdTe demonstrates that the lower binding energy of Mn-Te than Te-Te can cause the reduction of Te-Te binding defects in CdTe:Mn. In this report, the ternary alloy of Cd1-xMnxTe with Mn content in 0, 2, 21 % were prepared. The integrated intensity of photoluminescence (PL) spectra exhibits three times larger than other samples in sample with Mn content 21 %. The Stokes shift (SS) characterized by peak energy of PL spectra and bandgap energy of photoreflectance (PR) spectra show the greater value in Mn 21 % than others. The results indicate that the larger the Mn content in Cd1-xMnxTe, the more the composition fluctuations of Mn content in Cd1-xMnxTe showing larger SS. Scan electron microscope (SEM) images give the direct behavior of materialmicrostructures. The results indicates that Mn 21 % sample have relatively flat surface of the film. Micro-Raman spectra also exhibit the diminished intensity of scattering modes of A1 and E that are related to Te-Te binding defects. The consequence is that the better condition of Mn content is 21 % in Cd1-xMnxTe for superior optical and material properties.
The second part of the research is the study of optical behaviors of blue light emitting diodes (LEDs) with multiple quantum wells (MQs) containing part of Si doping. The Si doping layers are the first two, three, four, and five barriers of QWs in the growth sequence from sapphire substrate of four samples. The results indicate that the reduction of piezoelectric field in QWs were occurred in all samples for the blue shift in PL peak energy compared with the undoped Si sample. First four Si-doped barrier samples show larger PL spectra intensity with greater carrier localization in QWs and smaller quantum confined Stark effect (QCSE). Soft confinement potential of QWs was observed in first four Si-doped barrier samples due to the existence of strong absorption intensity in the bandgap energy between quantum wells and barriers. The uniform spreading of carriers in QWs were expected in this sample. Blue LED with first four Si-doped barrier, thus having better output power and external quantum efficiency (EQE) under high current injection. Therefore, first four Si-doped barrier is the favorite condition for light emission of blue LED having 8 QWs.
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