Vertically aligned single-crystal ZnO nanorods have been successfully fabricated on semiconducting GaN, Al0.5Ga0.5N, and AlN substrates through a vapor-liquid-solid process. Near-perfect alignment was observed for all substrates without lateral growth. Room-temperature photoluminescence measurements revealed a strong luminescence peak at approximately 378 nm. This work demonstrates the possibility of growing heterojunction arrays of ZnO nanorods on AlxGa1-xN, which has a tunable band gap from 3.44 to 6.20 eV by changing the Al composition from 0 to 1, and opens a new channel for building vertically aligned heterojunction device arrays with tunable optical properties and the realization of a new class of nanoheterojunction devices.
We report on the material, electrical, and optical properties of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled current transport in the 1.5 μm devices using thermionic field emission theory, and in the 4.0 μm devices using thermionic emission theory. We have obtained a good fit to the experimental data. Upon repeated field stressing of the 1.5 μm devices, there is a degradation in the current–voltage (I–V) characteristics that is trap related. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented based on experimental results. For devices fabricated on wafers with very low background free electron concentrations, there is a characteristic “punch-through” voltage, which we attribute to the interaction of the depletion region with the underlying low-temperature buffer layer. We also report GaN metal–semiconductor–metal photodetectors with high quantum efficiencies (∼50%) in the absence of internal gain. These photodetectors have a flat responsivity above the band gap (measured at ∼0.15 A/W) with a sharp, visible-blind cutoff at the band edge. There is no discernible responsivity for photons below the band-gap energy. We also obtained record low dark current of ∼800 fA at −10 V reverse bias. The dark current and ultraviolet photoresponse I–V curves are very flat out to VR>−25 V, and do not show evidence of trap-related degradation, or punch-through effects.
An effective, low cost, simple, and mask-free pathway is demonstrated for achieving density control of the aligned ZnO nanowires grown for large-scale applications. By a slight variation of the thickness of the thermally evaporated gold catalyst film, a significant change in the density of aligned ZnO nanowires has been controlled. The growth processes of the nanowires on an Al 0.5 Ga 0.5 N substrate has been studied based on the wetting behavior of gold catalyst with or without source vapor, and the results classify the growth processes into three categories: separated dots initiated growth, continuous layer initiated growth, and scattered particle initiated growth. This study presents an approach for growing aligned nanowire arrays on a ceramic substrate with the simultaneous formation of a continuous conducting electrode at the roots, which is important for device applications, such as field emission.One-dimensional (1D) ZnO nanostructures are considered to be one of the most important semiconducting nanomaterials for fabricating nanodevices with applications in optics, electronics, mechanics, and biomedical sciences. 1,2 The attraction of ZnO is the result of its high purity, high crystallinity, wide direct energy band gap (3.37 eV), large excitation binding energy (60 meV), piezoelectricity, and biocompatibility, as well as the divisive nanostructures. 3 Since the successful growth of aligned ZnO nanowires on a single-crystal substrate, 4-6 a system that may be very useful for vertical device fabrication has been found. As a result, great interest in acquiring more control over the alignments, including supporting substrates, distribution of nanowires, and density of nanowires, to maximally meet the requirements of nanodevices has been inspired.The vapor-liquid-solid (VLS) process is the most widely used technique for growing nanowires because of its relatively low cost and simple procedure. [4][5][6][7][8] Metal-organic chemical vapor deposition (MOCVD) has also been proven as an alternative method for aligned nanowires but with a much higher cost. 9,10 A wet chemistry process has recently been demonstrated as a powerful technique for growing aligned nanowires at a very low cost and over a very large surface area. 11-13 However, the density of nanowires grown on the surface still cannot be controlled unless a catalyst pattern created by a mask or lithography is applied.From the application point of view, the density of the aligned nanowires is very important since it is directly related to how the nanowires interact with each other optically, electronically, and mechanically. In field emission, 14,15 for example, an array of densely packed nanowires greatly reduces the field enhancement effect at the nanowire tip to a level not much different from a flat metal plate, while too loosely distributed nanowires cannot meet the desired requirement of high-emitting points. The ability to systematically control the density of the aligned nanowires so that optimal performance can be achieved by adjusting the space ...
InAlN electron-blocking layers (EBLs) are shown to improve the emission intensity and to mitigate the efficiency droop problem in III-nitride-based visible light-emitting diodes (LEDs). Using an In0.18Al0.82N EBL in blue LEDs, we have achieved a significant improvement in the electroluminescence emission intensity and a mitigated efficiency droop compared to similar LEDs without an EBL or with an Al0.2Ga0.8N EBL. This indicates that an In0.18Al0.82N EBL is more effective in electron confinement and reduces the efficiency droop possibly caused by carrier spill-over than conventional AlGaN EBLs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.