news digest ♦ LEDs
of multiple quantum well structures featuring 1.5 nm-thick AlGaN layers with a range of aluminium compositions up to 30 percent. Cross-sectional transmission electron microscopy analysis on this set of samples revealed no degradation in any of the structures. And probing these structures via photoluminescence studies showed that the greater the aluminium composition in the layer, the greater the suppression of the decline in efficiency at longer wavelengths.
Shioda and his co-workers have produced 600 µm by 600 µm LEDs with an active region featuring AlGaN layers, which were grown at the same temperature as the InGaN quantum wells. The output power of these LEDs increases with the proportion of aluminium in the interlayer.
Driven at 20 mW, a 532 nm LED incorporating an AlGaN layer with an aluminium content of 0.3 produces an output of 12 mW at an external quantum efficiency of 25.9 percent. One downside of this structure is its higher operating voltage – insertion of this aluminium layer increases the forward voltage from 3.5 V to 4.6V.
NCKU scientists strike gold at 2011 INPEX
The Taiwanese researchers have been honoured for their novel gallium nitride LED that can last 420 minutes, which they say is 140 minutes longer than traditional LEDs. With its compact size and high energy-saving properties, it is ideally suited to backlighting applications.
A research team led by Wen-Chau Liu of the Department of Electrical Engineering at National Cheng Kung University (NCKU) has won a gold award at the 2011 Invention & New Product Exposition (INPEX) for its highly efficient GaN based LEDs.
Held each year in Pittsburgh, INPEX offers over 1,000 innovations, new product ideas and technologies that can be licensed, manufactured, marketed or applied to a brand or product line. Taiwan took home 26 gold, 12 silver and 5 special awards this year, making it the biggest winner in one of the world-recognised invention shows. Among them, the gold-winning high current spreading efficiency GaN LED was the result of a
76
www.compoundsemiconductor.net August/September 2011
collaboration between Wen-Chau Liu, Wei-Chou Hsu and students Yi-Jung Liu, Chi-Hsiang Hsu and Jian-Kai Liou, all based in NCKU.
According to Liu, the new invention is 520μm² by 250μm² in size and can last 420 minutes, which is 140 minutes more than traditional LEDs which only last 280 minutes, having at least 50% of battery life than traditional LED lights.
The compact and high energy-saving LED is ideally suited for use as backlighting in laptops, cell phones and outdoor billboards.
“Companies are asking about technology transfer and we have already applied for patent, so the possibility in commercialisation is very high,” Liu said.
Wen-Chau Liu has also won gold medals in the 2010 International Exhibition of Inventions of Geneva and the 2010 International Trade Fair “Ideas-Inventions-New Products” (iENA) Nuremberg, Germany.
LEDs speed up effective diagnosis of tuberculosis
A novel technique known as LED-FM can diagnose tuberculosis more quickly and efficiently than current methods.
Researchers led by Luis E. Cuevas and Mohammed Yassin from the Liverpool School of Tropical Medicine have found that LEDs can be used to diagnose tuberculosis (TB).
The findings have important implications for the ways in which diagnosis for the endemic infectious disease, TB, can be done in poor countries. They
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180