Mechanisms and Applications of Steady-State Photoluminescence Spectroscopy in Two-Dimensional Transition-Metal Dichalcogenides

Abstract

Two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors exhibit many important structural and optoelectronic properties, such as strong light− matter interactions, direct bandgaps tunable from visible to near-infrared regions, flexibility and atomic thickness, quantum-confinement effects, valley polarization possibilities, and so on. Therefore, they are regarded as a very promising class of materials for next-generation state-of-the-art nano/micro optoelectronic devices. To explore different applications and device structures based on 2D TMDs, intrinsic material properties, their relationships, and evolutions with fabrication parameters need to be deeply understood, very often through a combination of various characterization techniques. Among them, steady-state photoluminescence (PL) spectroscopy has been extensively employed. This class of techniques is fast, contactless, and nondestructive and can provide very high spatial resolution. Therefore, it can be used to obtain optoelectronic properties from samples of various sizes (from microns to centimeters) during the fabrication process without complex sample preparation. In this article, the mechanism and applications of steady-state PL spectroscopy in 2D TMDs are reviewed. The first part of this review details the physics of PL phenomena in semiconductors and common techniques to acquire and analyze PL spectra. The second part introduces various applications of PL spectroscopy in 2D TMDs. Finally, a broader perspective is discussed to highlight some limitations and untapped opportunities of PL spectroscopy in characterizing 2D TMDs.

An Instantaneous Recombination Rate Method for the Analysis of Interband Recombination Processes in ZnO Crystals

“…As discussed previously, this behavior shows the characteristic features for a secondorder recombination rate and agrees with the PL decay reported in Equation (6). Therefore, from decay curves acquired at different values of the laser fluence F, the instantaneous lifetime was determined via numerical derivative and the initial values were fitted as a function of F by using Equation (8).…”

“…By integrating (6) we obtain φ(t) = φ(0) exp − t 0 w e f f (t )dt , which shows again that the simple case of a time-independent instantaneous recombination rate corresponds to simple single-exponential (first order) kinetics.…”

“…Surface traps, bulk defects and band offsets at interfaces significantly affect the rates of charge recombination [1][2][3][4] and thus of PL intensity, by introducing efficient non-radiative recombination pathways and/or by affecting the average spatial separation between electrons and holes. As a consequence, the optical PL spectroscopy of semiconductors is often employed to assess crystal quality and surface/interface characteristics [5][6][7][8][9][10]. Very often, these assessments do not involve quantitative analysis and phenomenological approaches are sufficient for extracting the desired information.…”

Optoelectronic Properties of MoS2 in Proximity to Carrier Selective Metal Oxides

“…Steady‐state PL spectroscopy can be used to probe, amongst others, the many‐body complexes, optoelectronic quality, stability, defects, doping densities, charge transport behaviors, and device performance of TMDCs, as summarized in a recent review by Tebyetekerwa et al. [ 23 ] MoS 2 has distinct excitonic transitions, that can be observed in the PL spectra at room temperature. The different PL peaks of the spectrum give insights into the materials energy transitions related to the electronic band structure.…”

Orientation of Individual Anisotropic Nanocrystals Identified by Polarization Fingerprint

“…The information carried by the polarization state of light is harnessed in a wide variety of applications, ranging from emerging modern technologies such as quantum information technology − or spintronics − to material characterization of organic , or inorganic matter . A particularly intriguing aspect is its use in optical spectroscopy on nanoscale materials, such as two-dimensional transition-metal dichalcogenides, − one-dimensional (1D) nanowires and zero-dimensional quantum dots (QDs), − because the polarization encodes the fingerprint of the electronic eigenstate symmetry . A prominent example is the emergence of linearly polarized photoluminescence (PL), for example, induced by a break of rotational symmetry in colloidal QDs (cQDs), by strong shape anisotropies in quantum rods, or by the crystal structure in lead halide perovskites. , Circularly polarized PL, on the other hand, is widely used to access the magnetic-field-dependent state splitting in undoped ,− as well as in doped QDs. − This state splitting is evidenced by a spectral shift of the right circularly polarized (σ + ) and the left circularly polarized (σ – ) PL and causes an increase of the degree of circular polarization with magnetic field because of the resulting state occupation.…”