Novel Devices ♦ news digest
In order for the semiconductor to emit light, its electrons must be raised to a higher energy level by means of energy-rich light, for instance. The silicon vacancy defect leads to the generation of additional energy levels in the so-called band gap.
Stepladder for electrons
Vladimir Dyakonov, chair of the Department for Experimental Physics VI, explains the process with a simple analogy; “In a regular, perfectly structured silicon carbide crystal, the electron must overcome a big hurdle with only one step. This requires a lot of energy. Due to the defect, the electron is provided with a ladder. It can clear the hurdle with two steps, requiring less energy.”
When the electrons “fall back” from the higher energy level to the lower one, this type of silicon carbide emits infrared rather than ultraviolet light. According to Astakhov, such light is better suited to transfer information in an optical fibre. “This requires wavelengths in the infrared range,” the physicist says.
Application in a quantum computer
The modified SiC is particularly promising for another application – as a semiconductor and storage medium in novel quantum computers. “Since their invention, transistors have shrunk from several tens of micrometers to approximately 10nm, i.e. about one thousandth of their original size,” Astakhov notes.
If the miniaturisation continues at this speed, transistors would have to consist of one individual atom in ten years’ time. At this scale, however, special physical laws apply, namely the laws of quantum mechanics.
The computers of today process information with the binary system (0/1): Electricity flows or it does not. A quantum computer processes information in the form of so-called qubits. These can be based on the spin of electrons. In simplified terms, the spin represents their angular momentum. It can point in several directions, for which reason it can represent much more information than a classical bit.
The information lies in the defect “In this field of research, a lot of attention has
The Würzburg physicists conducted their experiments in collaboration with researchers from Saint Petersburg. By “hitting” the silicon crystals simultaneously with light and radio waves, they were able to manipulate the spins in a targeted way, enabling them to store and retrieve information at will.
What the physicists are particularly enthusiastic about is the fact that the silicon vacancy qubits in a densely packed crystal behave almost like atoms with well-defined, very sharp optical resonances. “This is very unusual,” Astakhov adds.
“This is a new research field where experimental data of other study groups are still scarce at the moment. However, the reviewers looked favourably on our experiments and immediately recommended our manuscript for publication. We are very curious to know how the scientific community will react to our study,” Astakhov reveals. The first reaction has already materialised; Astakhov has been invited to present his results at the Quantum Science Symposium in Cambridge.
Spin quantum computers not only require the ability to process information, but also to store
January/February 2013
www.compoundsemiconductor.net 223
been paid to the colour centres in diamond, which exhibit defects that are similar to those of our silicon carbide,” says Astakhov.
Their qubits can be easily addressed, changed or read even at room temperature. However, the diamond production technology is not nearly as advanced as that of silicon semiconductors. “For this reason, there is a worldwide hunt for quantum systems that combine the advantages of diamond and silicon within one material,” Astakhov explains.
The Würzburg physicists believe SiC with a vacancy defect to be a suitable candidate for this purpose. “The missing atom also has as a consequence that the crystal lattice lacks an electron, which in turn is equivalent to the spin that can be used as information carrier in a quantum computer,” Dyakonov explains. What’s more, the SiC technology is fairly well developed. LEDs, transistors, micro-electro-mechanical components or sensors made from this material are already on the market.
Exposing the material to light and radio waves
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