Intrinsic photoluminescence Stokes shift in semiconductors demonstrated by thin-film CdS formed with pulsed-laser deposition

Inherent photoluminescence Stokes shift in GaAs

“…Although the phenomenon has been known since the nineteenth century for atomic transitions and multiple decades for semiconductors (particularly for GaAs) [1][2][3], we are not aware of attempts to pinpoint the intrinsic chromaticity defining PL Stokes shift of GaAs. In the current Letter, augmenting our previous works on p-type GaAs [4], CdS [5], and ZnO [6], we identify the inherent GaAs Stokes shift of semi-insulating (SI) GaAs. Additionally, the work emphasizes the association of the Urbach tail and Stokes shift in predominately covalently bonded semiconductors.…”

“…Ideally, the experimental PL result, which is represented by the square symbols in Fig. 2 pointing to E PL 1.4247 0.0011 eV, ought to be excited with a non-lasing moderate optical stimulus to avoid distortion of the inherent recombination channels [5]. However, in contrast to ZnO crystals and doped GaAs wafers, we were not able to excite RT PL of SI-GaAs using Xenon lamp sources.…”

“…The result reveals the influence of the crystal bonding, i.e., ionic versus covalent, on the Stokes shift value [1]. While CdS and ZnO exhibit Δ Stokes > hν LO [5,6], for GaAs, Δ Stokes ≪ hν LO , because of the proximity of the dielectric constants. The extremes with ε ∞ ε 0 are the element semiconductors Ge and Si for which Eq.…”

“…The determination of the intrinsic Stokes energy displacement (Δ Stokes ) between the energy locations of the optical band gap (E g;o ) and the PL peak (E PL ) requires measurements at RT to favor band-to-band recombination upon the formation of excitons and strong TR signals to be able to precisely point out the value of E g;o [5]. The latter condition is the major obstacle because, as in the current work, top-quality crystalline materials possess thicknesses exceeding by far the single digit μm range.…”

“…Within this scatter, the theoretical value of Δ Stokes is expected. The latter is expressed with the formula below incorporating Fan's classical relation for the semiconductor's selfenergy [5,16]:…”