We reported on the successful synthesis of the Nd：YAG （Nd：Y3Al5O12） nano-powders by using urea as the precipitant with the microwave assisted homogeneous precipitation （MAHP） method. The different microstructural characteristics of the Nd：YAG nano-powders were affected by the concentrations of （Y3＋＋Nd3＋） and Al3＋ （[Y3＋＋Nd3＋]=0.06 mol/L, [Al3＋]=0.1 mol/L）, aging time （6 d） and aging condition （in vessel）. The optimum microstructural characteristics of the high quality Nd：YAG nano-powders leading to transparent Nd：YAG ceramics including the pure YAG phase, the smallest crystallite size, a uniform crystallite size distribution, less density defects, uniform micro-components and the proper molar ratio of （Y3＋＋Nd3＋） and Al3＋ （0.6148） were discussed.
We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-Ⅱ quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Also, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures.
Chemical mechanical polishing (CMP) was used to etch various GaN materials, such as GaN layers on sapphire and silicon carbide substrates grown by metal-organic chemical vapor deposition and thick GaN layers grown by physical vapor transport. It was found that CMP could reveal the dislocations in GaN surfaces due to a selective etching component. After the optimization of CMP condition, the surface finish improved and the subsurface damage was almost completely removed, demonstrated by atomic force microscopy and an electron back-scattered diffraction technique. This study established the correlation between the dislocation density and film quality. The crystalline perfection and optical properties of GaN layers were characterized by high resolution X-ray diffraction and photoluminescence.
Siche DietmarRost Hans-JoachimSchulz TobiasAlbrecht Martin
