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In x Ga 1−x N / GaN ͑x = 0.09, 0.14, 0.24, and 0.3͒ multiple-quantum-wells ͑MQWs͒ samples, with a well width of about 4.5 nm, were achieved by utilizing r-plane sapphire substrates. Optical quality was investigated by means of photoluminescence ͑PL͒, cathodoluminescence, and time resolved PL measurements ͑TRPL͒. Two distinguishable emission peaks were examined from the low temperature PL spectra, where the high-and low-energy peaks were ascribed to quantum wells and localized states, respectively. Due to an increase in the localized energy states and absence of quantum confined Stark effect, the quantum efficiency was increased with increasing indium composition up to 24%. As the indium composition reached 30%, however, pronounced deterioration in luminescence efficiency was observed. The phenomenon could be attributed to the high defect densities in the MQWs resulted from the increased accumulation of strain between the InGaN well and GaN barrier. This argument was verified from the much shorter carrier lifetime at 15 K and smaller activation energy for In 0.3 Ga 0.7 N / GaN MQWs. In addition, the polarization-dependent PL revealed that the degree of polarization decreased with increasing indium compositions because of the enhancement of zero-dimensional nature of the localizing centers. Our detailed investigations indicate that the indium content in a-plane InGaN/GaN MQWs not only has an influence on optical performance, but is also important for further application of nitride semiconductors.

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Stress migration ͑SM͒ and electromigration ͑EM͒ were widely used to study the performance of interconnection process of metal/via formation in copper dual damascene of wafers. Necking and voids at the via bottom were important in causing failures in tests of stress migration and electromigration. In this report, the contamination of the bottom of via, which results in poor step coverage, the adhesion of seed layers, and poor copper grain formation are identified to be the underlying causes of the necking and void formation after the first EM and SM tests are performed. The contamination of the via formation processes included via etching, trench etching, and barrier/seed layer depositions. A well-shaped via profile can be optimized using three methods, the first involves Cu/SiN interface stress, the second involves Cu grain growth, and the third involves post via etching clean study. Eliminating the contamination of the via bottom and optimizing step coverage and adhesion of the barrier seed layers improve the EM and SM performance from time-to-fail ϭ 13 to 59 s, in the copper-related processes for fabricating 300 mm wafers using technology that is beyond 0.13 m technology.

The authors have used metal organic chemical vapor deposition to grow InGaN∕GaN multiple quantum well (MQW) nanostripes on trapezoidally patterned c-plane sapphire substrates. Transmission electron microscopy (TEM) images clearly revealed that the MQWs grew not only on the top faces of the trapezoids but also on both lateral side facets along the [0001] direction defined by the selected area electron diffraction pattern. Meanwhile, dislocations that stretched from the interfaces between the GaN and the substrates did not pass through the MQWs in the TEM observation. Microphotoluminescence measurements verified that the luminescence efficiency from a single nanostripe was enhanced by up to fivefold relative to those of regular thin film MQW structures. Observation of the cathodoluminescence identified the areas of light emission and confirmed that enhanced emission occurred from the nanostripes.