This page contains a Flash digital edition of a book.
Industry  Infrared detectors


process and epitaxial growth, the maximum operating temperature for these detectors – which featured 384 by 288 pixels with a 15 µm pitch and had a cut-off wavelength of 5 µm at 80 K – increased from 90 K to 120 K.


More recently, Sofradir’s engineers have started to apply these improvements to the company’s Scorpio detector, which has 640 by 512 pixels and a 5 µm cut- off wavelength. This detector’s operating temperature has increased from 90 K to 120 K and the power required for cooling has halved.


“ We go from something like 3.5 W to 1.7 W, depending on the size of the components,” says Billon-Lanfrey. The company took this to the SPIE Defense Security and Sensing conference held in Orlando last April. At this gathering its main rival was a form of InSb-based detector featuring an InAlSb or InAsSb barrier layer and sporting an operating temperature of up to 150 K.


However, according to Billon-Lanfrey, the higher operating temperature came at the expense of an inferior cut-off wavelength, which suppressed the dark current. “In the temperature range we are looking at, the maximum emission is in the four-to-five micron band. With a cut-off at four microns, there aren’t enough photons to achieve good image quality in poor weather conditions.” Inverted architecture Another aim for the French outfit is to demonstrate a ‘p- over-n’ MCT detector in 2012. “We expect to have a focal plane temperature of between 150 K and 170 K,” says Billon-Lanfrey, who adds that it will take roughly another two years before this technology is used in production.


Switching from the conventional n-over-p MCT detector to a p-over-n variant enables a substantial increase in operating temperature by cutting dark current by one- to-two decades. The fabrication of such a device requires far greater modification of the production process than that which occurred during the introduction of a superior passivation process. But the engineers at Sofradir don’t have to start from scratch. That’s because they and their colleagues at CEA-Leti started to develop a p-over-n technology for long- wavelength detectors in 2003, which is now used on the Scorpio LW that has a 9.5 µm cut-off wavelength.


Sofradir is continuing to develop its p-over-n technology for long-wave detectors and apply it to medium-wave cousins. Billon-Lanfrey believes that this should enable the production of medium-wave detectors operating at up to 150 K. To reach even higher temperatures will require the introduction of more complex architectures that may incorporate a barrier layer. Today CEA-Leti is working on the development of this technology, which requires a shift from liquid phase epitaxy to MBE growth of the epilayers.


Unmanned aerial vehicles (UAV) may be fitted with mercury cadmium telluride detectors that provide infrared images over a vast spectral range.The cooling system for these detectors draws heavily on the batteries fitted to the UAV


.However,this demand can be reduced by


raising the operating temperature of the detector through switching from the traditional ‘n-over-p’design to a ‘p-over-n’variant,or by introducing more complex epitaxial layers.The Scan Eagle UAV pictured here weighs 40 lbs,has a ten-foot wingspan,is invisible to radar,can fly over a designated battle space for up to 15 hours and can transmit real-time imagery directly to its home link


26 www.compoundsemiconductor.net January/February 2012


The plan is to demonstrate this form of detector in 2014- 2015 and start production two years’ later. If Sofradir can hit these goals and its near-term targets, it will deliver significant improvements in the performance of infrared detectors throughout the remainder of this decade. Commercial success appears destined to follow, giving those working in the infrared valley yet more achievements to be proud of.


© 2012 Angel Business Communications. Permission required.


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  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212  |  Page 213  |  Page 214  |  Page 215  |  Page 216  |  Page 217  |  Page 218  |  Page 219  |  Page 220  |  Page 221  |  Page 222  |  Page 223  |  Page 224  |  Page 225  |  Page 226  |  Page 227  |  Page 228  |  Page 229  |  Page 230  |  Page 231  |  Page 232  |  Page 233  |  Page 234  |  Page 235  |  Page 236  |  Page 237  |  Page 238  |  Page 239  |  Page 240  |  Page 241