Ultrafast Exciton Dynamics and Two‐Photon Pumped Lasing from ZnSe Nanowires

Abstract

The carrier recombination dynamics in ZnSe nanowires (NWs) remain poorly understood despite more than a decade of research since their inception in 2001. Herein, through a comprehensive pump fluence‐ and temperature‐dependent two‐photon excitation (TPE) study, a clear picture of the carrier relaxation pathways, intrinsic lifetimes, exciton oscillator strengths, and exciton‐phonon interactions is presented for this NW system. Contrary to a common perception that the higher pump intensities needed to achieve two‐photon‐excited photoluminescence correspond to a higher exciton density threshold (nth) for two‐photon pumped lasing, it is found that a much lower nth is needed to achieve lasing with TPE compared to single‐photon excitation (SPE) of the same ZnSe NWs. This measurement is further supported by the greatly enhanced lasing action photostability characteristics of the ZnSe NWs under TPE. These findings have significant implications on the design and the tailoring of the optoelectronic properties of nanowire lasers.

Photoluminescence and surface photovoltage properties of ZnSe nanoribbons

“…The DD band can be fitted into three sub-bands, respectively, centered at 623 nm (DD1), 563 nm (DD2) and 525 nm (DD3) (the dash lines in spectrum 7), which agrees well with the previous reports [15][16][17][18]. The previous researches about temperature-dependent PL reveal the thermally activated dynamic processes of photogenerated electrons transfer from shallower to deeper energy states [17,19,26]. Here, at low excitation intensity, the dominant band of DD1 emission in the PL spectrum (spectrum 1) indicates the recombination of photogenerated carriers from DD1 states prior to the shallower states and conduction band, due to the thermal activated relaxation process of the photogenerated electrons.…”

“…For the further discussion on the above results, the spectrum 7 (about 560-lW excitation power) was fitted with Gauss functions. The DD band can be fitted into three sub-bands, respectively, centered at 623 nm (DD1), 563 nm (DD2) and 525 nm (DD3) (the dash lines in spectrum 7), which agrees well with the previous reports [15][16][17][18]. The previous researches about temperature-dependent PL reveal the thermally activated dynamic processes of photogenerated electrons transfer from shallower to deeper energy states [17,19,26].…”

“…The typical room temperature photoluminescence (PL) studies on ZnSe nanostructures show two characteristic bands in the emission spectrum, including the band edge (BE) emission band and the deep defect (DD)-related broad emission band [14]. The DD states are usually treated as the recombination centers, which has been widely studied with PL techniques, including the PL of ZnSe which grows under Zn-and Se-rich atmosphere, temperature-dependent, time-and spatial-resolved PL [15][16][17][18][19]. However, little attention has focused on the trap effect of the DD states correlating with photoelectric response understood as separation of photogenerated carriers, which competes with the radiative pathway for PL emission [20].…”

Spin-Related Micro-Photoluminescence in Fe3+ Doped ZnSe Nanoribbons

“…In its PL spectrum, there are three emission peaks at 467, 553 and 630 nm, respectively. The first emission peak at 467 nm is assigned to near band-edge exciton emissions, whose nature needs further identification for the bandgap of pure ZnSe material is at about 2.7 eV (460 nm) at room temperature [27]. The second (D1) and third (D2) emission peak at 553 and 630 nm are related to Fe 3+ d-d transition, which will be discussed later.…”

Toward electrically driven semiconductor nanowire lasers

“…[52] The NW structure can therefore provide high-quality materials to cover the green wavelength and offer a promising solution to this "green gap" issue. Materials used for developing the visiblewavelength NW laser include CdS (490 nm), [53] InGaN (530 nm) [54], ZnSe (~460 nm) [55], and CdSSe (530 and 637 nm) [56].…”