软交换网络中中继媒体网关的研究与设计

提出了IP中继媒体网关的一种实现模型,并介绍了其功能。对其进行了模块划分,并对各个模块的功能和实现做了简要说明。     

A comparison of TMG with TEG for the growth of InxGa1−xAs

MOCVD growth of In_xGa_1?xAs from trimethylgallium (TMG), triethylgallium (TEG), trimethylindium (TMI) and arsine was studied over a wide range of growth conditions. It was found that the In_xGa_1?xAs strain with respect to InP is strongly influenced by the arsine concentration when grown with TEG and TMI. In contrast the In_xGa_1?xAs strain was independent of arsine concentration when grown with TMG and TMI. It was also observed that the growth rate of In_xGa_1?xAs is higher for TMG than for TEG with the same TMI and arsine flow. In addition an interaction between TEG and dimethylzinc (DMZ) was also observed. We show that MOCVD growth process involves many complex reactions and cannot be considered as a simple decomposition of each precursor. The interactions between precursors, which takes place in the gas phase or on the growing surface, has to be considered. We have utilized the TEG/arsine interaction for the growth of strain compensated superlattices by modulating the arsine flow into the reactor chamber while keeping the TEG and TMI constant. Structures with up to 100 periods of 100 Å of +1% In_0.6Ga_0.4As and 200 Å of ?0.5% In_0.5Ga_0.5As were grown with excellent characteristics.     

Effect of structural defects and chemical impurities on hall mobilities in low pressure MOCVD grown GaN

We have studied the effect that structural defects and chemical impurities have on the electron mobility in GaN films grown in a production scale metalorganic chemical vapor depositon system. Structural defects such as dislocations, stack-ing faults, twins, and amorphous regions in the buffer layer have been examined. In general, we have found that the structural defects are not the primary contributor to low mobility. However, there is one type of defect (“nanopipe”) that may be an important indirect contributor to mobility degradation by acting as a conduit into the film interior for impurities such as carbon and oxygen. We have also investigated the role that the principal impurities play in determining the electrical performance. Of particular concern was the presence of carbon result-ing from an incomplete dissociation of trimethylgallium precursor gas. Also present in the films were traces of oxygen, hydrogen, and aluminum, while heavy metals such as iron, chromium, and molybdenum were detected at or near the resolution limit of secondary ion mass spectrometry analysis. We present evidence for compensation by carbon at low carrier concentrations, which would help to explain the anomalous mobility behavior in GaN.