Cd_xPb_1–xS Alloy Nanowires and Heterostructures with Simultaneous Emission in Mid-Infrared and Visible Wavelengths

Abstract

Alloying of CdS and PbS could potentially provide an important semiconductor with a wide range of bandgaps, with bandedge emission from mid-infrared to visible green, for various optoelectronic applications. We investigate the possibility of CdPbS alloy formation in nanowire and nanobelt forms, especially the dependence of alloy composition on two different cooling routes. Our results show that rapid cooling immediately after the growth phase can lead to a high-quality uniform alloy with Cd composition larger than possible at thermal equilibrium and by natural cooling. On the contrary, unassisted natural cooling leads to the formation of axial or core-shell heterostructures, containing segments with pure CdS and CdPbS alloys with lower Cd content than through rapid cooling. Such heterostructures with green and mid-infrared emission provide simultaneous access to two widely separated wavelengths from a single monolithic structure and can be important for many applications. Our results can help identify strategies for growing nanostructures with uniform alloy of high Cd incorporation, core-shell structures with shell serving as a passivating or protecting layer, or interesting longitudinal heterostructures. Both various heterostructures and uniform alloys of these materials could be important for high-efficiency solar cells, novel detectors, and nanolasing in wide spectral ranges.

Strain Driven Spectral Broadening of Pb Ion Exchanged CdS Nanowires

“…Among these candidates, PbS and CdS hybridized structures have attracted a great interest because the band gaps of PbS/CdS compounds span from the infrared (PbS, 0.4–0.9 eV depending on size) to the visible range (CdS, 2.5 eV), thus covering nearly full solar spectrum. This is highly desirable for high efficiency photovoltaics . Therefore, it is expected that the integration of PbS to CdS parent phase may offer the synergetic effects including the favorable charge transport or the enhanced visible light absorption.…”

“…However, after IER, a response spectrum broadening from 510 to 650 nm was demonstrated in addition to the intrinsic response wavelengths peculiar to CdS nanowires. If we illuminated these photodetectors with an incident light of 550 nm wavelength and with an energy lower than the CdS band gap (but higher than the band gap of PbS), different photoresponses were observed from their current–voltage curves in Figure c. The sensors using Pb ion exchanged CdS nanowire achieve a photocurrent nearly three orders of magnitude larger than that for pure ones.…”

Flexible integration of free-standing nanowires into silicon photonics

“…The big challenge is to assemble FNWs into functional photonic circuits with low coupling loss and high precision. In previous papers, the coupling efficiency is usually low (e.g., below 5% 34, 36 ) due to the mismatch of mode overlapping and photon momentum.…”

“…These highly uniform one-dimensional nanostructures, with diameters of a few to hundreds of nanometers, show surface roughness down to atomic level (i.e., the same order of the silica nanofiber), offering an opportunity for deep-subwavelength optical waveguiding with low optical loss 24, 25 . Moreover, benefiting from the bottom-up process that synthesizes nanowires from atomic-size nucleation sites, the nanoscale transverse cross sections of FNWs allow large lattice mismatch in single-crystalline structures 26–28 , which offers much greater material diversity for active and nonlinear applications compared with the traditional top-down technique 29–34 . In order to merge the advantages of the bottom-up and the top-down techniques, previously there have been some successful studies on integrating FNWs with on-chip waveguides 35–37 .…”

Wavelength‐Tunable Micro/Nanolasers

“…At present, an incredible variety of alloying materials have been exhibited by researchers in the field. Research works on II–VI and III–V mesoscopic semiconductor materials, including Zn x Cd 1− x S, In x Ga 1− x N, CdS x Se 1− x , Zn x Cd 1− x S y Se 1− y , GaAs y P 1− y , Al x Ga 1− x P, Al x Ga 1− x N, Cd x Pb 1− x S, GaAs 1− x Sb x , and In x Ga 1− x P, have been a boost in recent years. For perovskites, MAPbX 3 (MA + = CH 3 NH 2 + , methylammonium; X − = I − , Br − , Cl − ), FAPbX 3 (FA + = CH(NH 2 ) 2 + , formamidinium), CsPbX 3 , CsSnX 3 , and CsPbMBr 3 (M 2+ = Sn 2+ , Cd 2+ , Zn 2+ ) have been demonstrated experimentally and provided a huge family of gain media choices.…”