Research and development have been carried out to apply the CVD diamond film to surface acoustic wave (SAW) devices. Several kinds of layered structures including a diamond layer have been investigated by the calculations and experiments, and it has been found that the diamond SAW has great advantages for the application of high-frequency SAW devices with high SAW velocity, small temperature coefficient and high power durability. Practical SAW devices have been successfully fabricated with ZnO/diamond/Si and SiO 2 /ZnO/diamond/Si structures whose characteristics are superior to those with conventional SAW materials.

No abstract

InGaN-based blue light-emitting diodes (LEDs) with different quantum well (QW) thicknesses were grown on freestanding GaN substrates with low threading dislocation densities (TDDs) and on c-plane sapphire substrates. In the case of thin QWs of 3nm in thickness, the external quantum efficiencies (EQEs) of LEDs on GaN substrates, as well as those on sapphire substrates, decreased with increasing forward current, indicating that carrier localization is in play on both types of substrates. For thicker 5-nm-thick QWs, the EQEs of LEDs grown on GaN substrates improved at high current densities, while those on sapphire substrates decreased even at low current densities. The LED with 5-nm-thick QWs on the GaN substrate mounted p-side down and molded with epoxy showed EQE as high as 26% at 125A∕cm2. Cathodoluminescence observations of the active layers on GaN substrates revealed that the expansion of nonradiative areas related to TDDs, which are responsible for the deterioration of the EQE of the LED on the sapphire substrate, had been suppressed.

Surface acoustic wave (SAW) characteristics of the SiO2/interdigital-transducer(IDT)/ZnO/diamond structure were studied theoretically and experimentally. It was found that the 2nd mode in this structure can provide a zero temperature coefficient of frequency (T C F) as well as high velocity of 10,000 m/s and a large electromechanical coupling coefficient of 1.4%. Utilizing this wave, a 2.5 GHz narrow-band SAW filter was successfully fabricated with IDTs of 0.9 µm finger width, which resulted in superior characteristics for a retiming filter with a small insertion loss of 6.7 dB, Q value of 660 and small frequency deviation of 100 ppm in the temperature range from -40 to 85°C. The insertion loss is smaller than any other retiming filters which have ever been reported with quartz, a conventional SAW material, and also the frequency deviation with temperature is smaller than that in the case of ST-cut quartz.

No abstract