Improvement of optical properties of InGaN-based red multiple quantum wells.

The realization of red-emitting InGaN quantum well (QW) is a hot issue in current nitride semiconductor research. It has been shown that using a low-Indium (In)-content pre-well layer is an effective method to improve the crystal quality of red QWs. On the other hand, keeping uniform composition distribution at higher In content in red QWs is an urgent problem to be solved. In this work, the optical properties of blue pre-QW and red QWs with different well width and growth conditions are investigated by photoluminescence (PL). The results prove that the higher-In-content blue pre-QW is beneficial to effectively relieve the residual stress. Meanwhile, higher growth temperature and growth rate can improve the uniformity of In content and the crystal quality of red QWs, enhancing the PL emission intensity. Possible physical process of stress evolution and the model of In fluctuation in the subsequent red QW are discussed. This study provides a useful reference for the development of InGaN-based red emission materials and devices.

Strong localization effect and carrier relaxation dynamics in self-assembled InGaN quantum dots emitting in the green.

Strong localization effect in self-assembled InGaN quantum dots (QDs) grown by metalorganic chemical vapor deposition has been evidenced by temperature-dependent photoluminescence (PL) at different excitation power. The integrated emission intensity increases gradually in the range from 30 to 160 K and then decreases with a further increase in temperature at high excitation intensity, while this phenomenon disappeared at low excitation intensity. Under high excitation, about 40% emission enhancement at 160 K compared to that at low temperature, as well as a higher internal quantum efficiency (IQE) of 41.1%, was observed. A strong localization model is proposed to describe the possible processes of carrier transport, relaxation, and recombination. Using this model, the evolution of excitation-power-dependent emission intensity, shift of peak energy, and linewidth variation with elevating temperature is well explained. Finally, two-component decays of time-resolved PL (TRPL) with various excitation intensities are observed and analyzed with the biexponential model, which enables us to further understand the carrier relaxation dynamics in the InGaN QDs.

[Effect of tetromethylpyrazine and aminoguanidine on expression of vascular endothelial growth factor in kidney of diabetic rats].

OBJECTIVE: To investigate the therapeutic mechanism of tetromethylpyrazine and aminoguanidine on diabetic nephropathy. METHODS: Diabetic rats were induced by streptozotocin. They were divided into 5 groups: normal control group (group C), untreated diabetic group (group DM), tetromethylpyrazine treated group (group TMP), aminoguanidine treated group (group AG) and tetromethylpyrazine and aminoguanidine treated group (group TMP+AG). The expression of vascular endothelial growth factor (VEGF) in renal cortex of the rats in each group was observed by immunohistochemical staining after 12 weeks. RESULTS: The expression of VEGF in renal cortex of the rats in group TMP+AG and group C was alike. The expression of VEGF in renal cortex of group TMP and group AG decreased significantly as compared with that of group C, but was still above normal level. CONCLUSION: The therapeutic mechanism of tetromethylpyrazine and aminoguanidine on diabetic nephropathy may be inhibiting the over-expression of VEGF in kidney of diabetic rats.