Hierarchical growth of GaN nanowires for light emitting diode applications
26 Feb 2016-Proceedings of SPIE (International Society for Optics and Photonics)-Vol. 9748, pp 974820
TL;DR: In this paper, the hierarchical growth of GaN nanowires by dynamically adjusting the growth parameters using pulsed flow metalorganic chemical vapor deposition (MOCVD) technique was reported.
Abstract: Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers and nanofluidic biochemical sensors. In this study, we report on the hierarchical growth of GaN nanowires (NWs) by dynamically adjusting the growth parameters using pulsed flow metalorganic chemical vapor deposition (MOCVD) technique. We carried out two step growth processes to grow hierarchical GaN NWs. At the first step the GaN NWs were grown at 950°C and in the second stage, we suitably decreased the growth temperature to 710°C to grow the hierarchical structures. The surface morphology, structural and optical characterization of the grown hierarchical GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and photoluminescence (PL) measurements, respectively. These kind of hierarchical NWs are promising to allow flat band quantum structures that are shown to improve the efficiency of light-emitting diodes.
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TL;DR: It was found that use of a pulsed MOCVD process allowed thenanowire diameter to remain constant after the nanowires had emerged from the selective growth mask, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the Nanowires.
Abstract: This paper reports a scalable process for the growth of high-quality GaN nanowires and uniform nanowire arrays in which the position and diameter of each nanowire is precisely controlled. The approach is based on conventional metalorganic chemical vapor deposition using regular precursors and requires no additional metal catalyst. The location, orientation, and diameter of each GaN nanowire are controlled using a thin, selective growth mask that is patterned by interferometric lithography. It was found that use of a pulsed MOCVD process allowed the nanowire diameter to remain constant after the nanowires had emerged from the selective growth mask. Vertical GaN nanowire growth rates in excess of 2 μm/h were measured, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the nanowires. The paper reports transmission electron microscopy and photoluminescence data.
597 citations
TL;DR: In this paper, a review of the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN Nanorods is presented. But, the authors also discuss problems and open questions, which may impose obstacles during the future development of a GaN-based LED technology.
Abstract: In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.
495 citations
TL;DR: In this paper, the vapor-liquid-solid crystal growth mechanism was briefly introduced for the general synthesis of nanowires of different compositions, sizes, and orientation, and the implication of these heterojunction nanometrics in light-emission and energy conversion was discussed.
Abstract: The following article is based on the Outstanding Young Investigator Award presentation given by Peidong Yang of the University of California, Berkeley, on April 14, 2004, at the Materials Research Society Spring Meeting in San Francisco.Yang was cited for “innovative synthesis of a broad range of nanowires and nanowireheterostructure materials, and the discovery of optically induced lasing in individual nanowire devices.” One-dimensional nanostructures are of both fundamental and technological interest.They not only exhibit interesting electronic and optical properties associated with their low dimensionality and the quantum confinement effect, but they also represent critical components in potential nanoscale devices. In this article, the vapor–liquid–solid crystal growth mechanism will be briefly introduced for the general synthesis of nanowires of different compositions, sizes, and orientation. Unique properties, including light-emission and thermoelectricity, will be discussed. In addition to the recent extensive studies on “single-component” nanowires, of increasing importance is incorporating different interfaces and controlling doping profiles within individual single-crystalline nanowires. Epitaxial growth plays a significant role in fabricating such nanowire heterostructures. Recent research on superlattice nanowires and other nanostructures with horizontal junctions will be presented. The implication of these heterojunction nanowires in light-emission and energy conversion will be discussed. Ways to assemble these one-dimensional nanostructures will also be presented.
262 citations
TL;DR: It is shown that the insertion of an axial heterostructure drastically reduces the dark current with respect to the binary nanowires and enhances the photosensitivity factor up to 5 x 10(2) for an incoming light intensity of 5 mW/cm(2).
Abstract: We report the demonstration of single-nanowire photodetectors relying on carrier generation in GaN/AlN QDiscs. Two nanowire samples containing QDiscs of different thicknesses are analyzed and compared to a reference binary n-i-n GaN nanowire sample. The responsivity of a single wire QDisc detector is as high as 2 × 103 A/W at λ = 300 nm at room temperature. We show that the insertion of an axial heterostructure drastically reduces the dark current with respect to the binary nanowires and enhances the photosensitivity factor (i.e., the ratio between the photocurrent and the dark current) up to 5 × 102 for an incoming light intensity of 5 mW/cm2. Photocurrent spectroscopy allows identifcation of the spectral contribution related to carriers generated within large QDiscs, which lies below the GaN band gap due to the quantum confined Stark effect.
159 citations
TL;DR: The photocurrent behavior of single GaN n-i-n nanowires grown by plasma-assisted molecular-beam epitaxy on Si(111) presents a photoconductive gain in the range of 10(5)-10(8) and an ultraviolet (350 nm) to visible (450 nm) responsivity ratio larger than 6 orders of magnitude.
Abstract: We report on the photocurrent behavior of single GaN n–i–n nanowires (NWs) grown by plasma-assisted molecular-beam epitaxy on Si(111). These structures present a photoconductive gain in the range of 105–108 and an ultraviolet (350 nm) to visible (450 nm) responsivity ratio larger than 6 orders of magnitude. Polarized light couples with the NW geometry with a maximum photoresponse for polarization along the NW axis. The photocurrent scales sublinearly with optical power, following a I ∼ Pβ law (β < 1) in the measured range with β increasing with the measuring frequency. The photocurrent time response remains in the millisecond range, which is in contrast to the persistent (hours) photoconductivity effects observed in two-dimensional photoconductors. The photocurrent is independent of the measuring atmosphere, either in the air or in vacuum. Results are interpreted taking into account the effect of surface states and the total depletion of the NW intrinsic region.
152 citations