Abstract
Electronic band structures in semiconductors are uniquely determined by the constituent elements of the lattice. For example, bulk silicon has an indirect bandgap and it prohibits efficient light emission. Here we report the electrical tuning of the direct/indirect band optical transition in an ultrathin silicon-on-insulator (SOI) gated metal-oxide-semiconductor (MOS) light-emitting diode. A special Si/SiO2 interface formed by high-temperature annealing that shows stronger valley coupling enables us to observe phononless direct optical transition. Furthermore, by controlling the gate field, its strength can be electrically tuned to 16 times that of the indirect transition, which is nearly 800 times larger than the weak direct transition in bulk silicon. These results will therefore assist the development of both complementary MOS (CMOS)-compatible silicon photonics and the emerging “valleytronics” based on the control of the valley degree of freedom.
Highlights
Correspondence and requests for materials should be addressed to Electric tuning of direct-indirect optical transitions in silicon
The thicknesses of the quantum wells (QWs) are 4.3 and 6.0 nm. (Further details about device fabrication are provided in the Method section.) We find that the silicon QW diode exhibits strong and electrically-tuned direct optical transition, which would assist the development of complementary MOS (CMOS)-compatible silicon photonics[36,37,38]
The roughness of the buried oxide (BOX)/Si interface is much higher than that for front-gate oxide (FOX)/Si, whose potential variation could localize electrons and thereby form quantum dots (QDs) at the BOX/Si interface for positive VBG values. These QDs may cause strong NP transitions owing to the carrier confinement
Summary
Correspondence and requests for materials should be addressed to Electric tuning of direct-indirect optical transitions in silicon. An anomalously large valley splitting of a few tens of millielectron volts has been reported using a specially prepared Si/SiO2 interface formed on SIMOX (separation by implantation of oxygen) silicon on an insulator (SOI) substrate and a large gate electric field[17,18], suggesting a large momentum dispersion of the conductive electrons. Since such a large energy of the valley splitting is comparable to that of dopant impurities, we expect that these electrons can be directly dipole– coupled to holes, thereby emitting photons efficiently. The thicknesses of the QWs are 4.3 and 6.0 nm. (Further details about device fabrication are provided in the Method section.) We find that the silicon QW diode exhibits strong and electrically-tuned direct optical transition, which would assist the development of CMOS-compatible silicon photonics[36,37,38]
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