Electric tuning of direct-indirect optical transitions in silicon

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.

Electrically Engineered Band Gap in Two-Dimensional Ge, Sn, and Pb: A First-Principles and Tight-Binding Approach

“…A direct to indirect band gap transition occurs under an external electric field because the electric field enhances spontaneous polarization. This polarization is responsible for the direct to indirect band gap transition. , In addition, a perpendicular electric field reduces the band gap and thus, the transition is possible. ,, The data sets are summarized in Table . For low values of the electric field, the electronic gap is related to the spin–orbit coupling but for higher values of the external field the gap results from the difference of the electric potential on the different atomic sites.…”

“…This polarization is responsible for the direct to indirect band gap transition. 58,59 In addition, a perpendicular electric field reduces the band gap and thus, the transition is possible. 19,60,61 The data sets are summarized in Table 1.…”

Towards tunable graphene phononic crystals

“…The band structure parameters of solids can be adjusted via e.g., electrostatic gating, application of magnetic fields, or mechanical straining. Such tunability allows a plethora of experiments ranging from the exploration of phase transitions to changing the band structure topology [13][14][15][16][17][18], or increasing the electron mobility in silicon [19][20][21]. In contrast, phonons in PnCs do not react to an electrical or magnetic field.…”

A sub-wavelength Si LED integrated in a CMOS platform

“…These large-area emitters rely on the low surfaceto-volume ratio to minimize the non-radiative recombination on the surfaces, and thus it is challenging to reduce the emission area while keeping high efficiency. Other strategies include carrier confinement [16][17][18][19][20][21][22][23] , defect activation 17,[24][25][26] , field emission effect 27 , Purcell enhancement 23,26,28 , and avalanche effect [29][30][31] . To date, the Si emitter with the smallest emission area (≈1 μm 2 ), as well as the highest intensity (≈600 mW/cm 2 ), is reported by Schmitt et al 23 .…”