Volume 95, Issue 6, 15 March 2004
Index of content:
- DEVICE PHYSICS (PACS 85)
95(2004); http://dx.doi.org/10.1063/1.1646442View Description Hide Description
InGaN multiple-quantum-welllight-emitting diodes(LEDs) were grown on an AlN/sapphire template by metalorganic chemical vapor deposition. The crystalline quality was investigated by x-ray diffraction and electron-beam-induced current. The thermal stability of the LED was demonstrated by measurements of current–voltage, light output power–current, and electroluminescence(EL)spectra at different temperatures. The output power at 200 mA decreased by 7.3% for the LED on the template upon increasing temperature from 25 to 95 °C, while that for the LED on sapphire decreased by 23.9%. The peak external quantum efficiency decreased from 0.23% to 0.22% and from 0.15% to 0.10% for the LEDs on the template and on sapphire, respectively. The EL spectrum peak at 20 mA shifted to lower energy by 17.2 meV for the LED on the template upon increasing temperature, while that for the LED on sapphire shifted by 32.7 meV. The LED on the template exhibited a higher output power and a better thermal stability with respect to the conventional LED on sapphire using a low-temperature GaN buffer layer, which is due to the low threading dislocation density in the active layer and the high thermal conductivity of AlN layer.
95(2004); http://dx.doi.org/10.1063/1.1642288View Description Hide Description
Recent advances in magnetic recording technology are increasing the relevance of simulation to magnetic media design. In particular, the difficulties inherent in developing perpendicular recording technology require the write process to be modeled at an integrated level via the simulation of a nanoscale machine consisting of the media, the soft underlayer, and the moving head. These simulations need to be very efficient in order to permit extensive testing of both materials and drive specification. Thus, significant methodological improvements that increase the accuracy and speed of the micromagnetic modeling are required. In this article, a method for calculating the magnetic fields in a complex layered material with grained morphologies whose computational cost scales linearly with system size is presented. The speed, accuracy, and parallel efficiency of the method is demonstrated on both supercomputers and PC clusters using our Almaden-Yorktown micromagnetic simulator (AYM). The method and AYM software are then used to perform an example simulation of perpendicular magnetic recording, writing a “tribit” in a grained data layer.