news feature Let there be light A silicon laser would revolutionize telecommunications electronics and computing Squeezing light out of Silicon is no easy task, but Philip Ball discovers that esearchers are becoming more optimisti about its light-emitting abilities information age suffers from a and diligence, they say, the world s favourite negative charge carriers move into thin split personality. Deep beneath the semiconductor can be coaxed into emitting layers within the laser known as quantum ocean's surface, photons of light light. If an all-silicon laser couldbe created, it wells. Here the carriers recombine, releasing stream through optical fibres, carrying would revolutionize the design of supercom- their energy as a photon of light voice and Internet traffic between conti- puters and lead to new types of optoelectror But it is difficult to incorporate III-V nents. But before routing devices, comput- ic devices "says Leigh Canham of biomateri- alloys into silicon circuits. The two do not fit ers and telephones can use the data, this als company pSiMedica, a spin-off from the together because the spacing between the light-borne information must be converted UK Defence Evaluation and Research Agency atoms in the two materials, known as the into electronic signals With entirely optical (DERA). And if recent progress continues, lattice constant, is different. The ideal laser computers unlikely to replace electronics in that revolution may not be far off. diode for optical telecommunications-a he near future, this uneasy marriage of blend of indium, gallium, arsenic and phos- electrons and photons is likely to persist for Communication breakdown phorus, denoted In, Ga -As, PI-y- illus- ome time At the moment, laser diodes are used to turn trates the problem. This material emits light Improving the interface between silicon electronic signals into light pulses. These at a wavelength of about 1.5 micrometres, electronics and photonics is high on the miniature lasers are built from layers of dif- which is the optimum for transmission t Senda in the field of optoelectronics. Some ferent semiconductors, named Ill-V alloys through glass optical fibres, but has a lattice researchers believe that the solution lies in after the columns of the periodic table from constant thatis 8%bigger than that of silicon a/ring silicon's character Given patience which their constituents come. Positive and This means that atoms at the interface between the two the semiconductor “ Dislocations form near the interface and then thread through the Ill-v layer explain Vincent Crespi, a physicist at Pennsylvania State University. Because Glowing future: this layer is thinner Leigh Canham(left) than the silicon sub- and vincent Crespi strate, the light-emit ope to make silicon ting ill-v material st of the deformation, and the resulting defects 974 A@2001 Macmillan Magazines Ltd NaturEvoL40922febRuary2001www.nature.comWILL & DENI MCINTYRE/SPL DERA PENN STATE UNIV. The information age suffers from a split personality. Deep beneath the ocean’s surface, photons of light stream through optical fibres, carrying voice and Internet traffic between conti￾nents. But before routing devices, comput￾ers and telephones can use the data, this light-borne information must be converted into electronic signals. With entirely optical computers unlikely to replace electronics in the near future, this uneasy marriage of electrons and photons is likely to persist for some time. Improving the interface between silicon electronics and photonics is high on the agenda in the field of optoelectronics. Some researchers believe that the solution lies in reforming silicon’s character. Given patience negative charge carriers move into thin layers within the laser known as ‘quantum wells’. Here the carriers recombine, releasing their energy as a photon of light. But it is difficult to incorporate III–V alloys into silicon circuits. The two do not fit together because the spacing between the atoms in the two materials, known as the lattice constant, is different. The ideal laser diode for optical telecommunications — a blend of indium, gallium, arsenic and phos￾phorus, denoted InxGa11xAsyP11y — illus￾trates the problem. This material emits light at a wavelength of about 1.5 micrometres, which is the optimum for transmission through glass optical fibres, but has a lattice constant that is 8% bigger than that of silicon. This means that atoms at the interface between the two materials do not match up, and line￾like distortions form in the semiconductor. “Dislocations form near the interface and then thread through the III–V layer,” explains Vincent Crespi, a physicist at Pennsylvania State University. Because this layer is thinner than the silicon sub￾strate, the light-emit￾ting III–V material incurs most of the deformation, and the resulting defects and diligence, they say, the world’s favourite semiconductor can be coaxed into emitting light.“If an all-silicon laser could be created,it would revolutionize the design of supercom￾puters and lead to new types of optoelectron￾ic devices,” says Leigh Canham of biomateri￾als company pSiMedica, a spin-off from the UK Defence Evaluation and Research Agency (DERA). And if recent progress continues, that revolution may not be far off. Communication breakdown At the moment, laser diodes are used to turn electronic signals into light pulses. These miniature lasers are built from layers of dif￾ferent semiconductors, named III–V alloys after the columns of the periodic table from which their constituents come. Positive and 974 |wwwNATURE|VOL 409 | 22 FEBRUARY 2001 |www.nature.com news feature Let there be light A silicon laser would revolutionize telecommunications, electronics and computing. Squeezing light out of silicon is no easy task, but Philip Ball discovers that researchers are becoming more optimistic about its light-emitting abilities. Glowing future: Leigh Canham (left) and Vincent Crespi hope to make silicon optoelectronics a reality. © 2001 Macmillan Magazines Ltd