Optical properties of silicon nanowires from cathodoluminescence imaging and time-resolved photoluminescence spectroscopy

Excitons and excitonic fine structures in Si nanowires: Prediction of an electronic state crossover with diameter changes

“…15 As to scale (ii) and (iii), available photoluminescence spectra for Si nanowires show a complicated profile with relatively weak intensity compared to porous Si, broad peaks (the narrowest reported linewidth ν ∼ 85 meV at 7 K), 21 and long carrier decay time on the order of 1-10 3 µs. 20,34 These properties are strongly dependent on the wire size, morphology and surface passivation. 14,19,22,23 In this situation theoretical studies on excitonic properties of Si wires were usually compared to experimental results for porous Si, 29,30 which has a yet poorly understood morphology and interface.…”

“…(iii) In the "low energy" ∼10 −3 eV scale, we describe dark/bright excitonic states and predict how orbitally-allowed transitions (in scale (i)) become spin-forbidden due to the electron-hole exchange interaction, whereas the spin-allowed states in the orbitally-forbidden diameter region remain dark. The diameter dependence of the fine-structure splitting of excitonic states scales as 1/D 15,[18][19][20][21][22][23] properties. Yet, there appears to be limited understanding of the underlying electronic and excitonic properties.…”

On the origin of photoluminescence from silicon nanostructures: a new perspective

“…Hence, for small enough silicon nanocrystals where Δq becomes comparable to Δk, one expect enhancement of the direct radiative transitions with the decreasing size of the nanocrystal. Indeed, the discovery of efficient visible photoluminescence (PL) from porous silicon (PS) [3,4], SiNCs [5] and recently also from silicon nanowires [6][7][8], have led numerous researchers to suggest that the quantum confinement (QC) model, e.g., confinement of photo-excited carriers into small silicon nanoobjects, is responsible to the enhanced PL [2][3]5]. These discoveries have attracted much attention recently (for recent reviews see references [2,3,9,10]) as light-emitting silicon diodes can truly revolutionize modern integrated electronic circuits by allowing the integration of optoelectronic and microelectronic devices on the same (silicon) chip.…”

Assessing the capabilities and limitations of cathodoluminescence microscopy to investigate the optical properties of individual nanostructures

“…Thus, in the 100 nm thick In x Ga 1-x N (x = 14) sample, the lateral spread of the energy dissipation volume is smaller at incident beam energy 15 keV than at 2 keV. Dorint et al [5] used this effect to investigate the optical properties of individual porous silicon nanowires. The nanowires were found to be 60-70nm in diameter typically, with high resolution TEM confirming the presence of an amorphous-SiO 2 shell of 10-30 nm and a crystalline silicon core of about two-thirds of the outer diameter.…”