Light emission from direct bandgap hexagonal SiGe

Metastable Group IV Allotropes and Solid Solutions: Nanoparticles and Nanowires

“…491 However, only one group has reported the direct bandgap transition in the range of 0.3−0.7 eV in 2H-Si 1−x Ge x for x > 0.65 in very recent studies. 323,493 Emission values for the thick Ge 0.87 Sn 0.13 shell agree well with thin film data with similar composition and slight compressive strain including signal splitting at low temperatures due to the abrogation of degeneracy between heavy and light holes in the valence band. 140,498 Lower Sn content Ge/ Ge 0.96 Sn 0.04 core−shell NWs show four transitions fitted in a very broad emission, which are related to indirect and direct transitions in the Ge 0.96 Sn 0.04 shell and also the Ge core.…”

“…491 Very recently these materials have been realized with compositions of the 2H-Si 1−x Ge x alloy in the range x = 0.65−1.0. The first PL signals have been recorded for GaAs/2H-Si 1−x Ge x and GaAs/2H-Ge core/shell NWs 323,493 revealing tunable, direct bandgap materials in the energy range 0.3−0.7 eV. This is a very significant finding since the optical properties are comparable with III/V semiconductors, and thus applications including optical interconnect in computing, 494 optical sensing, 495 and silicon-based quantum photonic circuits 496 can be envisioned.…”

Thermodynamic driving force in the formation of hexagonal-diamond Si and Ge nanowires

“…In core/shell NWs [1,2,12,26,27], the process leading to the formation of the 2H-Si or Ge shells on top of wurtzite III-V (typically GaP or GaAs, respectively ) cores, differs significantly from the VLS growth. Here, an important role is expected to be played by the template effect of the cores [16].…”

“…hexagonal structure), the Si(Ge) shell on top has been obtained by Chemical Vapor Deposition (CVD). Both the Si [1] and SiGe [2,12] shells were unambiguously proven to have a high-quality 2Hcrystalline structure. All these advances [16] evidence how the allotropes of the group IV compounds may be an optimum solution to the need for a direct-gap material compatible with the Si technology.…”

“…The recent successes in the synthesis of Si crystals with the hexagonal diamond (2H, P63/mmc) crystalline structure [1][2][3][4][5][6][7][8][9][10] paved the way for the realization of on-chip light sources based on the hexagonal allotropes of group IV elements and highly compatible with the current Si technology. Although the 2H crystal phase retains the indirect nature of the 3C-Si band gap [10], theoretical predictions [11], confirmed by recent photoluminescence investigations, show a direct band-gap for 2H-Ge, which is preserved by alloying Ge with up to 30% Si [11,12].…”