TurboDisc K465i: Lighting Up Your Yield
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Application Note Advances in MB E-Grown GaN for Light-Emitting Diodes and High Electron Mobility Transistors Recently, GaN materials grown by plasma-assisted molecular beam epitaxy (MBE) have demonstrated significant improvements in material quality and device performance as growth conditions and device structures are refined. MBE results, which once lagged behind performance benchmarks set by MOCVD-grown materials, are now competitive with state-of-the-art devices. MBE-grown blue (485 nm) light-emitting diodes (LEDs) with output powers up to 0.87 mW at 20 mA forward current have been achieved. Electronic and thermal effects on recombination in these LED structures were investigated. High electron mobility transistors (HEMTs) with excellent power and efficiency were also demonstrated. Mobilities, power densities, and power-added efficiencies in excess of 1400 cmWs, 12 W/mm, and 46% at 4 GHz, respectively, were attained. Early achievements in nitride semiconductor devices were typically accomplished with GaN grown by metal organic chemical vapor deposition (MOCVD). With MBE results lagging, researchers once questioned whether MBE-grown nitrides suffered fundamental limitations to device performance. Current research demonstrates MBE results that are competitive with the materials for a number of devices. The MBE technique offers high uniformity across the substrate, sharp material interfaces, more flexible growth parameters, and material with lower point defect densities. MBE is compatible with a greater range of in-situ monitoring growth parameters and the deposited layers, enabling improved process control. Veeco's reliable MBE sources and versatile system growth chamber design provide the ideal research platform for producing high-performance, state-of-the-art The results discussed in this note demonstrate that with appropriate refinement of growth parameters and device design MBE-grown devices MOCVD-grown devices. LEDs produced from MOCVD-grown structures can produce up to several mW output power, while comparable MBE-grown devices typically yield output powers below 0.1 mW. With optimization of the barrier thickness MBE-grown blue LED with output HEMT performance has been improved to record levels using a two-step GaN buffer layer (to reduce

Figure 1: On-wafer output powers for three LED samples, each with five 3-nm InGaN wells. The barrier layer structure for each sample is indicated. The inset shows an EL spectrum of CURRENT Imfcl CURRENT (ÎÏIAJ CURRENT |niA) Figure 2: Optical properties of sample #3 (after packaging) as a function of current under dc and pulsed conditions. threading dislocation densities), the addition of carbon doping in the buffer layers to make them insulating, and capping with a SiN layer to Nitride structures were grown in a Veeco GEN II™ MBE system with a UNI-Bulb™ RF Plasma Source for nitrogen and...

thicker barriers) and increased higher electron background concentration from Si doping of the Optical properties of devices made from sample 3 were investigated. The inset in Figure 1 shows emission at 485 nm with a line width of 30 nm corresponds to an external quantum To separate electronic and thermal effects on emission, EL from Sample 3 was investigated under both pulsed and dc conditions. A duty cycle of 5% was chosen after verifying that device heating is minimal under these conditions. Figure 2 shows output power, emission wavelength, and peak width as a function of forward current...

leakage degrades transistor performance. In doped buffers, the carbon acts as a compensating acceptor and reduces buffer conductivity. The test structure for doping level investigations is shown in Figure 3(a), with carbon doping sequentially decreasing in the layers. Buffer leakage drain-source l-V curves on isolation patterns of HEMT structures with the etched away at the gate region. A leakage current of 1 mA/mm was chosen as the comparison point since this current, at three orders of magnitude lower than typical 2-DEG currents operation. Figure 3(b) shows the actual doping levels tested...