Here,
we design and engineer an axially asymmetric GaAs/AlGaAs/GaAs
(G/A/G) nanowire (NW) photodetector that operates efficiently at room
temperature. Based on the I-type band structure, the device can realize
a two-dimensional electron–hole tube (2DEHT) structure for
the substantial performance enhancement. The 2DEHT is observed to
form at the interface on both sides of GaAs/AlGaAs barriers, which
constructs effective pathways for both electron and hole transport
in reducing the photocarrier recombination and enhancing the device
photocurrent. In particular, the G/A/G NW photodetector exhibits a
responsivity of 0.57 A/W and a detectivity of 1.83 × 1010 Jones, which are about 7 times higher than those of the pure GaAs
NW device. The recombination probability has also been significantly
suppressed from 81.8% to 13.2% with the utilization of the 2DEHT structure.
All of these can evidently demonstrate the importance of the appropriate
band structure design to promote photocarrier generation, separation,
and collection for high-performance optoelectronic devices.
Nanowire photodetectors, which have the advantages of fast response and high photoelectric conversion efficiency, can be widely applied in various industries. However, the rich surface states result in large dark current and can hinder the development of high-performance nanowire photodetectors. In this paper, the influence and mechanism of sulfur surface passivation on the dark current of a single GaAs nanowire photodetector have been studied. The dark current is significantly reduced by about 30 times after surface passivation. We confirm that the origin of the reduction of dark current is the decrease in the surface state density. As a result, a single GaAs nanowire photodetector with low dark current of 7.18 × 10 pA and high detectivity of 9.04 × 10 cmHzW has been achieved. A simple and convenient way to realize high-performance GaAs-based photodetectors has been proposed.
We report the carrier dynamics in GaAsSb ternary alloy grown by molecular beam epitaxy through comprehensive spectroscopic characterization over a wide temperature range. A detailed analysis of the experimental data reveals a complex carrier relaxation process involving both localized and delocalized states. At low temperature, the localized degree shows linear relationship with the increase of Sb component. The existence of localized states is also confirmed by the temperature dependence of peak position and band width of the emission. At temperature higher than 60 K, emissions related to localized states are quenched while the band to band transition dominates the whole spectrum. This study indicates that the localized states are related to the Sb component in the GaAsSb alloy, while it leads to the poor crystal quality of the material, and the application of GaAsSb alloy would be limited by this deterioration.
The GaAsSb-based quantum well plays a very important role in optoelectronic devices due to its excellent wavelength tunability. When the dimension reduces, the quantum confinement effect will take place and the quantum well in nanowires will show many interesting characteristics. GaAsSbbased quantum-well nanowires are of contemporary interest. However, the properties of the quasitype-II structure in a single quantum well nanowire have been rarely investigated. Here, we grow GaAs/GaAs 0.92 Sb 0.08 /GaAs coaxial single quantum-well nanowires and discussed their powerdependent and temperature-dependent photoluminescence. We find that due to the small band offset of conduction bands, both type-I like and type-II like emission exist in our nanowires. When electrons obtain enough thermal energy through collisions or surrounding environment, they will overcome the barrier and diffuse to the GaAs conduction band, which contributes to the type-II like recombination. These results show the optical property of the quasi-type-II quantum well in nanowires, which can pave the way toward future nanoscale quantum well devices. Published by AIP Publishing.
The structural and optical properties of ZnO and ZnO/ZnS core-shell nanowires grown by a wet chemical method are investigated. The near-bandgap ultraviolet (UV) emission of the ZnO nanowires was enhanced by four times after coating with ZnS. The enhanced emission was attributed to surface passivation of the ZnO nanowires and localized states introduced during ZnS growth. The emission of the ZnO and ZnO/ZnS core-shell nanowires was attributed to neutral donor-bound excitons and localized excitons, respectively. Localized states prevented excitons from diffusing to nonradiative recombination centers, so therefore contributed to the enhanced emission. Emission from the localized exciton was not sensitive to temperature, so emission from the ZnO/ZnS core-shell nanowires was more stable at higher temperature. UV photodetectors based on the ZnO and ZnO/ZnS core-shell nanowires were fabricated. Under UV excitation, the device based on the ZnO/ZnS core-shell nanowires exhibited a photocurrent approximately 40 times higher than that of the device based on the ZnO nanowires. The differing photoresponse of the detectors was consistent with the existence of surface passivation and localized states. This study provides a means for modifying the optical properties of ZnO materials, and demonstrates the potential of ZnO/ZnS core-shell nanowires in UV excitonic emission and detection.
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