Luminescence of disordered semiconductors

Abstract

Luminescence of disordered (amorphous) semiconductors is due to a different microscopic mechanism compared to those being active in the luminescence of crystalline counterparts with long-range order. Electron and hole tail states, originating from dangling bonds, play the decisive role. Features typical for the amorphous semiconductor luminescence are discussed, namely: peculiar temperature dependence driven by the demarcation energy and distribution of luminescence decay times. Two theoretical models describing spectral shape of the emission band are examined: the phonon broadening model and the disorder broadening model. Theoretical band shapes are compared with experimental spectra found in amorphous elemental semiconductors. The concept of geminate and non-geminate electron–hole pairs is briefly debated. Multiple nonradiative recombination paths are mentioned as well as luminescence of impurities and defects.

Fine Structure Splitting of Phonon-Assisted Excitonic Transition in (PEA)2PbI4 Two-Dimensional Perovskites

“…This results in the Stokes shift between absorption and PL spectra. These are blue- and red-shifted from the zero-phonon line by , respectively, and form a mirror image, as schematically presented in Figure 2 c [ 36 , 37 ]. Usually, for a significant electron–phonon coupling, the phonon-assisted absorption or emission lines merge into a broad band—phonon wing—shown as envelope lines in Figure 2 c).…”

“…To interpret the origin of the two sidebands, we refer to Franck–Condon’s picture [ 36 , 37 ] presented schematically in Figure 2 b,c. When an electronic excitation results in a local lattice reconfiguration, the transition probability is modulated by the overlap between the vibrational lattice levels in the ground and the excited state of the lattice (see the upper and lower parabola in Figure 2 b).…”

“…The difference between the equilibrium position of atoms in the ground ( ) and the excited lattice state ( ) determines the average energy that is emitted by the lattice to reach the equilibrium position upon excitation or recombination. This corresponds to the average number of phonons emitted, referred to as the Huang–Rhys factor [ 36 , 37 ]. As the increases, the absorption and emission spectrum change from being dominated by the zero-phonon line to absorption and PL lines assisted by multiple phonon emission.…”

“…Therefore, we ascribe each of the sidebands to the merged responses of different order phonon replicas (different numbers of phonons participating in the transition), i.e., phonon wings [ 36 ], where SB involve phonons of different energies than SB . Similar side band features observed in the transmission or PL measurements of (PEA) PbI were also previously ascribed to phonon replicas [ 22 , 27 , 28 , 30 ].…”

Efficacy of boron nitride encapsulation against plasma-processing of 2D semiconductor layers

“…Photoluminescence is a far more sensitive measure of crystal quality and defect density for a high-quality, direct band gap semiconductor. The smallest deviation from perfect crystalline order can induce nonradiative recombination that reduces the primary PL efficiency 35 . Deviations from crystalline order can also introduce trap states that lead to photoluminescence that is red-shifted from the original PL peak location [35][36] .…”