n-ZnO Nanowires Research Articles

Use of the Thermal Chemical Vapor Deposition to Fabricate Light-Emitting Diodes Based on ZnO Nanowire/p-GaN Heterojunction

The fabrication and characteristics of grown ZnO nanowire/p-GaN heterojunction light-emitting diodes are reported. Vertically aligned ZnO nanowire arrays were grown on a p-GaN substrate by thermal chemical vapor deposition in quartz tube. The rectifying current-voltage characteristics indicate that a p-n junction was formed with a heterostructure of n-ZnO nanowire/p-GaN. The room temperature electroluminescent emission peak at 425 nm was attributed to the band offset at the interface between the n-ZnO nanowire and p-GaN and to defect-related emission from GaN; it was also found that the there exist the yellow band in the hetrojunction. It would be attributed to the deep defect level in the heterojunction.

High-Purity Ultraviolet Electroluminescence from n-ZnO Nanowires/p+-Si Heterostructure LEDs with i-MgO Film as Carrier Control Layer

Pure ultraviolet (UV) light emitting diodes (LEDs) using n-ZnO nanowires as an active layer were fabricated with an insulating MgO dielectric layer as a carrier control layer, where all depositions were continuously performed by metalorganic chemical vapor deposition. The current-voltage curve of the LEDs showed obvious rectifying characteristics, with a threshold voltage of about 7 V in the sample with 4 nm i-MgO. Under the forward bias of the samples with proper MgO thickness, a sharp UV electroluminescence, located at around 380 nm, was emitted from the active ZnO nanowires, while weak visible emission of around 450–700 nm were observed. The pure UV emission from the ZnO nanowires in the n-ZnO/i-MgO/p+-Si heterostructures was attributed to the electron accumulation in the ZnO by asymmetric band offset and preemptive hole tunneling from Si to ZnO by i-MgO.

<I>p</I>-Cu<SUB>2</SUB>O/<I>n</I>-ZnO Nanowires on ITO Glass for Solar Cells

In this paper, the fabrication and characterization of a heterojunction solar cell based on p-Cu2O/n-ZnO nanowires on ITO glass are presented. ZnO aligned nanocrystal seed layer is firstly prepared by RF magnetron sputtering technique, and then vertical ZnO nanowire arrays with an acicular crystal structure are obtained by using a chemical bath deposition processing. The results indicate that the ZnO nanowires with a diameter of about 50 nm and 500 nm in length can be easily obtained. The absorption and transmittance of the ZnO nanowires are studied. It is also noted that the Cu2O can fill well into the space between ZnO nanowires by an electrodeposition process. Furthermore, the effect of the Cu2O orientation on the cell performance is also presented.

Growth and Properties of Aligned ZnO Nanowires and Their Applications to n-ZnO/p-Si Heterojunction Diodes

Aligned n-ZnO nanowires were synthesized via simple thermal evaporation process by using metallic zinc powder in the presence of oxygen on p-silicon (Si) substrate. The as-synthesized aligned ZnO nanowires were characterized in terms of their structural and optical properties by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction process (XRD) and room-temperature photoluminescence (PL) properties. The detailed structural and optical studies revealed that the as-grown nanowires are single crystalline with the wurtzite hexagonal phase and exhibit good optical properties. From application point of view, the as-grown aligned n-ZnO nanowires on p-Si substrates were used to fabricate heterojunction diodes. The fabricated heterojunction diodes exhibited good electrical (I-V) properties with the turn-on voltage of approximately 1.0 V. A temperature-dependant (from 25 degrees C approximately 130 degrees C), I-V characteristics for the fabricated device was also demonstrated in this paper. The presented results demonstrate that the simply grown aligned n-ZnO nanowires on p-Si substrate can be efficiently used for the fabrication of efficient heterojunction devices.

Ordered Nanowire Array Blue/Near‐UV Light Emitting Diodes

[∗] S. Xu , C. Xu , Y. Liu , Y. F. Hu , R. S. Yang , Q. Yang , Prof. Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, Georgia, 30332–0245 (USA) E-mail: zlwang@gatech.edu J. H. Ryou , H. J. Kim , Z. Lochner , S. Choi , Prof. R. Dupuis School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, Georgia, 30332–0245 (USA) ZnO-based light emitting diodes (LEDs) have been considered as a potential candidate for the next generation of blue/ near-UV light sources, [ 1 ] due to a direct wide bandgap energy of 3.37 eV, a large exciton binding energy of 60 meV at room temperature, and several other manufacturing advantages of ZnO. [ 2 ] While the pursuit of stable and reproducible p-ZnO is still undergoing, [ 3,4 ] heterojunctions of n-ZnO and p-GaN are employed as an alternative approach in this regard by considering the similar crystallographic and electronic properties of ZnO and GaN. [ 5–7 ] Compared with the thin fi lm/thin fi lm LEDs, [ 5,6 , 8 ] which may suffer from the total internal refl ection, n-ZnO nanowire/p-GaN thin fi lm heterostructures are utilized in order to increase the extraction effi ciency of the LEDs by virtue of the waveguiding properties of the nanowires. [ 9–11 ] But in all of these cases, the n-ZnO nanowires are randomly distributed on the substrate, which largely limits their applications in high performance optoelectronic devices. Here in this work, we demonstrate the capability of controlling the spatial distribution of the blue/near-UV LEDs composed of position controlled arrays of n-ZnO nanowires on a p-GaN thin fi lm substrate. The device was fabricated by a conjunction of low temperature wet chemical methods and electron beam lithography (EBL). The EBL could be replaced by other more convenient patterning techniques, such as photolithography and nanosphere lithography, rendering our technique low cost and capable of scaling up easily. Under forward bias, each single nanowire is a light emitter. By Gaussian deconvolution of the emission spectrum, the origins of the blue/nearUV emission are assigned particularly to three distinct electronhole recombination processes. By virtue of the nanowire/thin fi lm heterostructures, these LEDs give an external quantum effi ciency of 2.5%. This approach has great potential applications in high resolution electronic display, optical interconnect, and high density data storage. The design of the LED is shown in Figure 1a . Ordered ZnO nanowire arrays were grown on p-GaN (Figure 1 b–d), [ 12–14 ]

Laterally Grown n-ZnO Nanowire/p-GaN Heterojunction Light Emitting Diodes

The fabrication and characteristics of laterally grown ZnO nanowire/p-GaN heterojunction light emitting diodes are reported. The ZnO nanowires were grown using a direct single-step method on a prepared p-GaN patterned substrate. The rectifying current–voltage characteristics indicate that a p-n junction was formed with a heterostructure of n-ZnO nanowire/p-GaN. The room-temperature electroluminescent emission peak at 430 nm was attributed to the band offset at the interface between n-ZnO nanowire and p-GaN and defect-related emission from GaN.

Ultraviolet Electroluminescence Emission from n-Type ZnO/p-Type Si Crossed Nanowire Light-Emitting Diodes

The optical characteristics of an n-type ZnO/p-type Si crossed nanowire (NW) light-emitting diode (LED) were investigated in this study. N-ZnO nanowires (NWs) were synthesized by thermal chemical vapor deposition, and p-Si NWs were fabricated by etching a single crystalline Si wafer. The p–n heterojunction LED formed by the cross of the n-ZnO and p-Si NWs selected from the NWs prepared in this work exhibited the current rectifying behavior with the turn-on voltage of 1.3 V. Our investigation of the photoluminescence spectrum of the as-grown n-ZnO NWs and electroluminescence spectrum of the n-ZnO/p-Si crossed NW LED reveals that both spectra have the same position of peaks at 390 nm. This result indicates that the UV emission from the crossed NW LED is mostly attributed to the band-to-band transition of electrons in the ZnO NW.

Photonic Devices in Some Low Dimensional Systems

Results of using low temperature growth approach (lower than 100 oC) to control the growth of ZnO nanowires are presented. The effect of different parameters on the growth is highlighted. Time resolved low temperature photoluminescence (PL) was used to investigate surface recombination and its relation to the nanowires diameters. Finally hybrid light emitting diodes (LEDs) based on p-type polymers and n-ZnO nanowires grown on amorphous substrates is fabricated and characterized. This hybrid organic-inorganic technology can provide a suitable replacement of conventional lighting tubes.

Scalable Fabrication of Nanowire Photonic and Electronic Circuits Using Spin-on Glass

We present a method which can be used for the mass-fabrication of nanowire photonic and electronic devices based on spin-on glass technology and on the photolithographic definition of independent electrical contacts to the top and the bottom of a nanowire. This method allows for the fabrication of nanowire devices in a reliable, fast, and low cost way, and it can be applied to nanowires with arbitrary cross section and doping type (p and n). We demonstrate this technique by fabricating single-nanowire p-Si(substrate)-n-ZnO(nanowire) heterojunction diodes, which show good rectification properties and, furthermore, which function as ultraviolet light-emitting diodes.

The study of electrical characteristics of heterojunction based on ZnO nanowires using ultrahigh-vacuum conducting atomic force microscopy

The electrical performances of the heterojunction of n-ZnO nanowires with p-Si substrate at the nanometer scale have been characterized using an ultrahigh-vacuum conducting atomic force microscopy. Compared with the expected values of 1.0–2.0 reported in p-n junction in the previous studies, the abnormally high diode ideality factor (⪢2) was obtained. It elucidates that a ZnO–Si p-n junction can be modeled by a series of diodes, the actual ZnO–Si junction diode and two Schottky diodes at the metal/ZnO and metal/Si junctions. The tunneling across p-n junction would also play a role in the externally measured high ideality factor.

Mechanical and Electrical Properties of ZnO-Nanowire/Si-Substrate Junctions Studied by Scanning Probe Microscopy

Scanning tunneling spectroscopy was used to check the tunneling IiV characteristics of junctions formed by n-ZnO nanowires deposited on Si substrates with n- and p-type electrical conductivity (i.e. n-ZnO nanowire/ n-Si and n-ZnO nanowire/p-Si junctions, respectively). Simultaneously, several phenomena which in∞uence the measured IiV spectra were studied by atomic force microscopy. These in∞uencing factors are: the deposition density of the nanowires, the possibility of surface modiflcation by tip movement (difierence in attraction forces between nanowires and the p-Si and n-Si) and the aging of the surface. ZnO nanowires (ZnO NWs) are expected to play an important role as functional units in future nanoscale devices. Di‐culty in reproducible p-type doping of ZnO (nominally undoped ZnO is of n-type) demands a method of electrical conductivity type veriflcation which is cost efiective and easy to perform. Scanning probe microscopy (SPM) has high spatial resolution and can probe local electronic properties of the material. Several interesting applications of SPM techniques on ZnO NWs were reported (conducting-atomic force microscopy (AFM) [1{3], NW bending [4], patterning growth locations [5]). In this work scanning tunneling spectroscopy (STS) is used for the identiflcation of pin junction behavior of ZnO NWs on Si substrate. For n-ZnO NWs deposited on Si substrate, we expect | depending on the Si electrical conductivity type | the presence (for p-Si substrate) or the absence (for n-Si) of the tunneling IiV curves of diode slope indicating

Cu 2O/n-ZnO nanowire solar cells on ZnO:Ga/glass templates

We report the deposition of p-Cu2O onto vertical n-ZnO nanowires prepared on ZnO:Ga/glass templates. With the sputtered Cu2O, the nanowires became club0like (nanowire with a head). Experimental results indicate that sputtered Cu2O also formed nano-shells surrounding the ZnO cores. The p-Cu2O/n-ZnO nanowire heterostructure exhibits rectifying behavior with a sharp turn on at ∼0.46 V. Furthermore, the short-circuit photocurrent density, open circuit voltage, fill factor and conversion efficiency of the fabricated solar cell were 2.35 mA cm−2, 0.13 V, 0.29 and around 0.1%, respectively.

Modeling the Carrier Mobility in Nanowire Channel FET

AbstractWe report on the extraction of carrier type, and mobility in semiconductor nanowires by adopting experimental nanowire field-effect transistor device data to a long channel MISFET device model. Numerous field-effect transistors were fabricated using n-InAs nanowires of a diameter of 50 nm as a channel. The I-V data of devices were analyzed at low to medium drain current in order to reduce the effect of extrinsic resistances. The gate capacitance is determined by an electro-static field simulation tool. The carrier mobility remains as the only parameter to fit experimental to modeled device data. The electron mobility in n-InAs nanowires is evaluated to µ = 13,000 cm2/Vs while for comparison n-ZnO nanowires exhibit a mobility of 800 cm2/Vs.