scholarly journals Boosted Ultraviolet Photodetection of AlGaN Quantum-Disk Nanowires via Rational Surface Passivation

2021 ◽  
Author(s):  
Chen Huang ◽  
Fangzhou Liang ◽  
Huabin Yu ◽  
Meng Tian ◽  
Haochen Zhang ◽  
...  
Keyword(s):  
Dark Current ◽  
Surface Passivation ◽  
Solution Treatment ◽  
Surface States ◽  
Volume Ratio ◽  
Ammonium Hydroxide ◽  
Underlying Mechanism ◽  
Rational Surface ◽  
Quantum Disk ◽  
Order Of Magnitude

Abstract Self-assembled AlGaN nanowires (NWs) are regarded as promising structures in the pursuit of ultraviolet photodetectors (UV PDs). However, AlGaN nanowire-based PDs currently suffer from degraded performance partially owing to the existence of outstanding surface-related defects/traps as a result of its large surface-to-volume-ratio feature. Here, we propose an effective passivation approach to suppress such surface states via tetramethyl ammonium hydroxide (TMAH) solution treatment. We successfully demonstrate a fabrication of UV PDs using TMAH-passivated AlGaN quantum-disk NWs and investigate their optical and electrical properties. Particularly, the dark current can be significantly reduced by an order of magnitude after surface passivation, thus leading to the improvement of photoresponsivity and detectivity. The underlying mechanism for such boost can be ascribed to the effective elimination of oxygen-related surface states on the nanowire surface. Consequently, an AlGaN nanowire UV PD with a low dark current of 6.22×10-9 A, a large responsivity of 0.95 A W-1, and a high detectivity of 6.4×1011 Jones has been achieved.

Surface Passivation and the Ultrafast Optical Response of Low-Temperature-Grown GaAs

1995 ◽  
Vol 378 ◽  
Author(s):  
H. H. Wang ◽  
J. F. Whitaker ◽  
K. Al-Hemyari ◽  
S. L. Williamson
Keyword(s):  
Low Temperature ◽  
Dark Current ◽  
Surface Passivation ◽  
Surface States ◽  
Time Response ◽  
Temporal Response ◽  
Dc Voltage ◽  
Ultrafast Optical ◽  
Metal Semiconductor Metal ◽  
Low Temperature Grown Gaas

AbstractMetal-semiconductor-metal photodetectors fabricated using low-temperature-grown GaAs have been passivated using AlGaAs cap layers in order to understand the influence of surface states and fields on the properties of these detectors. It has been found that passivation has little effect on the time response or persistent photoconductive tails associated with the detectors, but that responsivity and dark current can be enhanced in certain circumstances. The dependence of the temporal response on optical fluence and dc-voltage bias were observed for both passivated and unpassivated detectors.

Investigation of Surface Passivation in InAs/GaSb Strained-Layer-Superlattices Using Picosecond Excitation Correlation Measurement and Variable-Area Diode Array Surface Recombination Velocity Measurement

2005 ◽  
Vol 891 ◽  
Author(s):  
Zhimei Zhu ◽  
Elena Plis ◽  
Abdenour Amtout ◽  
Pallab Bhattacharya ◽  
Sanjay Krishna
Keyword(s):  
Infrared Detectors ◽  
Surface Passivation ◽  
Surface Recombination ◽  
Surface States ◽  
Depletion Region ◽  
Surface Recombination Velocity ◽  
Diode Array ◽  
Ammonium Sulfide ◽  
Picosecond Excitation ◽  
Recombination Velocity

ABSTRACTThe effect of ammonium sulfide passivation on InAs/GaSb superlattice infrared detectors was investigated using two complementary techniques, namely, picosecond excitation correlation (PEC) measurement and variable-area diode array (VADA) surface recombination velocity (SRV) measurement. PEC measurements were conducted on etched InAs/GaSb superlattice mesas, which were passivated in aqueous ammonium sulfide solutions of various strengths for several durations. The PEC signal's decay time constant (DTC) is proportional to carrier lifetimes. At 77 K the PEC signal's DTC of the as-grown InAs/GaSb superlattice sample was 2.0 ns, while that of the unpassivated etched sample was reduced to 1.2 ns by the surface states at the mesa sidewalls. The most effective ammonium sulfide passivation process increased the PEC signal's DTC to 10.4 ns. However it is difficult to isolate surface recombination from other processes that contribute to the lifetime using the PEC data, therefore a VADA SRV measurement was undertaken to determine the effect of passivation on surface recombination. The obtained SRV in the depletion region of the InAs/GaSb superlattice and GaSb junction was 1.1×106 cm/s for the unpassivated sample and 4.6×105 cm/s for the passivated sample. At 77 K the highest R0A value measured in our passivated devices was 2540 W cm2 versus 0.22 W cm2 for the unpassivated diodes. The results of the lifetime, the SRV and the R0A measurements indicate that ammonium sulfide passivation will improve the performance of InAs/GaSb superlattice infrared detectors.

Comparative Optical Studies of Chemically Synthesized Silicon Nanocrystals

1996 ◽  
Vol 452 ◽  
Author(s):  
Gildardo R. Delgado ◽  
Howard W.H. Lee ◽  
Susan M. Kauzlarich ◽  
Richard A. Bley
Keyword(s):  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Surface Passivation ◽  
Theoretical Calculations ◽  
Dominant Role ◽  
Blue Emission ◽  
Surface States ◽  
Si Nanocrystals ◽  
Optical And Electronic Properties ◽  
Passivation Layers

AbstractWe studied the optical and electronic properties of silicon nanocrystals derived from two distinct fabrication procedures. One technique uses a controlled chemical reaction. In the other case, silicon nanocrystals are produced by ultrasonic fracturing of porous silicon layers. We report on the photoluminescence, photoluminescence excitation, and absorption spectroscopy of various size distributions derived from these techniques. We compare the different optical properties of silicon nanocrystals made this way and contrast them with that observed in porous silicon. Our results emphasize the dominant role of surface states in these systems as manifested by the different surface passivation layers present in these different fabrication techniques. Experimental absorption measurements are compared to theoretical calculations with good agreement. Our results provide compelling evidence for quantum confinement in both types of Si nanocrystals. Our results also indicate that the blue emission from very small Si nanocrystals corresponds to the bandedge emission, while the red emission arises from traps.

Biological Functionalization of Carbon Nanotubes

2004 ◽  
Vol 823 ◽  
Author(s):  
Ranjani Sirdeshmukh ◽  
Kasif Teker ◽  
Balaji Panchapakesan
Keyword(s):  
Biological Sciences ◽  
Carbon Nanotubes ◽  
Surface Area ◽  
Surface States ◽  
Volume Ratio ◽  
Surface Phenomenon ◽  
Antibody Molecule ◽  
Detection Systems ◽  
Biological Surface ◽  
Functionalization Of Carbon Nanotubes

AbstractCarbon nanotubes are known for their exceptional mechanical and unique electronic properties. The size dependant properties of nanomaterials have made them attractive to develop highly sensitive sensors and detection systems. This is especially true in biological sciences, where the efficiency of detection systems reflect on the size of the detector and the sample required for detection. At approximately 1.5 to 10nm wide, and approximately 1.5 to 2μm long, the use of carbon nanotubes as sensors in biological systems would greatly increase the sensitivity of detection and diagnostics, for a reduced sample size consisting of few individual proteins and antibodies. Since all the atoms in carbon nanotubes are surface atoms, binding proteins or antibodies to the surfaces can greatly affect their surface states, and thus their electrical and optical properties. This effect can be exploited as a basis for detecting biological surface reactions in a single protein or antibody attached to carbon nanotube surfaces.In this paper, we show the binding of fluorescently tagged antibodies in phosphate buffered saline on the surfaces of carbon nanotubes. Investigations using a confocal microscope suggest a significant interaction of the antibodies with the surfaces of the nanotubes, the intensity depending on incubation time. Since the surface area to volume ratio of CNTs is high, the use of surfactant to separate the nanotubes creates a greater surface area for antibody attachment. The interaction between CNTs and antibodies is seen to be primarily due to adsorptive surface phenomenon, between the nanotube sidewalls and antibody molecule clusters.

Morphology and I-V Characteristics of Electrochemically Deposited Zinc Oxide on Silicon

2021 ◽  
Vol 20 (3) ◽  
pp. 32-36
Author(s):  
Ahmad Bukhairi Md Rashid ◽  
Mastura Shafinaz Zainal Abidin ◽  
Shaharin Fadzli Abd Rahman ◽  
Amirjan Nawabjan
Keyword(s):  
Zinc Oxide ◽  
Electrochemical Deposition ◽  
Dark Current ◽  
Room Temperature ◽  
Volume Ratio ◽  
Deposition Process ◽  
X Ray ◽  
Current Voltage ◽  
Electrochemically Deposited ◽  
A Current

This paper reported on the electrochemical deposition of zinc oxide (ZnO) on p-silicon (p-Si) (100) substrate in the mixture of 0.1 M of zinc chloride (ZnCl2) and potassium chloride (KCl) electrolyte at a volume ratio of 1:1, 3:1 and 5:1 namely Sample A, B and C. The deposition process was done in room temperature with a current density of 10 mA/cm2 for 30 minutes. Prior to the experiment, all samples were treated by RCA cleaning steps. All samples were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results show that all samples have the same morphology of a flake-like structure with different Zn:O ratio that were 2.81, 2.35 and 2.49 for samples A, B and C. The current-voltage (I-V) characteristic graph was obtained by dark current measurement using Keithley SMU 2400 and the threshold voltage (Vth) values were determined at 2.21 V, 0.85 V and 1.22 V for sample A, B and C respectively which correspond with the Zn:O ratio where the highest value of Zn:O ratio can be found in sample A and the lowest in sample B. Based on these results, it shows that electrochemical deposition technique is capable of being used to deposit the flake-like structure ZnO on semiconductor material to form the p-n junction which behaves like a diode. The value of Vth seems to be depended on the ratio between Zn and O. Higher ratio of Zn and O will cause the higher value of intrinsic carrier concentration and built in potential which will increase the Vth value.

Influence of surface passivation on electric properties of individual GaAs nanowires studied by current–voltage AFM measurements

2016 ◽  
Vol 56 (2) ◽  
Author(s):  
Pavel Geydt ◽  
Prokhor A. Alekseev ◽  
Mikhail S. Dunaevskiy ◽  
Tuomas Haggrén ◽  
Joona-Pekko Kakko ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Surface Passivation ◽  
Surface States ◽  
Electric Properties ◽  
Conductive Atomic Force Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Gaas Nanowires ◽  
Current Voltage

Current–voltage (I–V) characteristics of vertical p-GaAs nanowires (NWs) covered by different surface passivation materials were experimentally measured by conductive atomic force microscopy (C-AFM). The obtained I–V curves for individual NWs with a diameter of 100 nm covered with AlGaAs, GaN, GaP or InP shell layers were compared to analyse the influence of surface passivation on the density of surface states and choose the most beneficial passivating material for technological applications. We have found the absence of a Schottky barrier between the golden catalytic cap on the top of a NW and the nanowire situated below and covered with an ultrathin GaP passivating layer. It was suggested that passivating material can arrange the heterostructure configuration with the GaAs NW near the Au cap. The latter mechanism was proposed to explain a strong energy barrier found in nanowires covered with InP passivation. AlGaAs passivation affected the forward threshold voltage of nanowires for NWs, which was measured simultaneously with the resistivity of each individual vertical structure from an array by means of AFM in the regime of measuring the I–V curves and onefold calculations. We made an attempt to develop the methodology of measurement and characterization of electric properties of passivated NWs.

scholarly journals Temperature-dependent photoluminescence properties of porous fluorescent SiC

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Weifang Lu ◽  
Abebe T. Tarekegne ◽  
Yiyu Ou ◽  
Satoshi Kamiyama ◽  
Haiyan Ou
Keyword(s):  
Surface Passivation ◽  
Surface States ◽  
Atomic Layer ◽  
Emission Peak ◽  
Photoelectron Spectra ◽  
Porous Structures ◽  
Temperature Dependent ◽  
Time Resolved ◽  
Pl Emission ◽  
Temperature Dependent Photoluminescence

Abstract A comprehensive study of surface passivation effect on porous fluorescent silicon carbide (SiC) was carried out to elucidate the luminescence properties by temperature dependent photoluminescence (PL) measurement. The porous structures were prepared using an anodic oxidation etching method and passivated by atomic layer deposited (ALD) Al2O3 films. An impressive enhancement of PL intensity was observed in porous SiC with ALD Al2O3, especially at low temperatures. At temperatures below 150 K, two prominent PL emission peaks located at 517 nm and 650 nm were observed. The broad emission peak at 517 nm was attributed to originate from the surface states in the porous structures, which was supported by X-ray photoelectron spectra characterization. The emission peak at 650 nm is due to donor-acceptor-pairs (DAP) recombination via nitrogen donors and boron-related double D-centers in fluorescent SiC substrates. The results of the present work suggest that the ALD Al2O3 films can effectively suppress the non-radiative recombination for the porous structures on fluorescent SiC. In addition, we provide the evidence based on the low-temperature time-resolved PL that the mechanism behind the PL emission in porous structures is mainly related to the transitions via surface states.

Properties of Surface States on GaN and Related Compounds and Their Passivation by Dielectric Films

2002 ◽  
Vol 743 ◽  
Author(s):  
Hideki Hasegawa ◽  
Tamotsu Hashizume
Keyword(s):  
Plasma Treatment ◽  
Surface State ◽  
Surface Passivation ◽  
Hydrogen Plasma ◽  
Surface States ◽  
Ex Situ ◽  
Near Surface ◽  
Ecr Plasma ◽  
Good Surface ◽  
Donor States

ABSTRACTThis paper reviews the authors′ recent efforts to clarify the properties of electronic states near surfaces of GaN and AlGaN by using variousin-situandex-situcharacterization techniques, including UHV contact-less C-V, photoluminescence surface state spectroscopy (PLS3), cathode luminescence in-depth spectroscopy (CLIS),and gateless FET techniques that have been developed by the authors’ group.As a result, a model including a U-shaped surface state continuum, having a particular charge neutrality level, combined with frequent appearance of near-surface N-vacancy related deep donor states having a discrete level at Ec - 0.37eV is proposed as a unified model that can explain large gate leakage currents and current collapse in AlGaN/GaN HFETs. Hydrogen plasma treatment and SiO2deposition increase N-vacancy related deep donors. Reasonably good surface passivation can be achieved by ECR-plasma SiNx films and by ECR-plasma oxidized Al2O3films both combined with ECR N2plasma treatment.

Role of Mesoporous TiO2 Surface States and Metal Oxide Treatment on Charge Transport of Dye Sensitized Solar Cells

2010 ◽  
Vol 1270 ◽  
Author(s):  
Mariyappan Shanmugam ◽  
Braden Bills ◽  
Mahdi Farrokh Baroughi
Keyword(s):  
Activation Energy ◽  
Dark Current ◽  
Hafnium Oxide ◽  
Photovoltaic Performance ◽  
Dye Sensitized Solar Cells ◽  
Surface States ◽  
Atomic Layer ◽  
Dye Sensitized ◽  
Layer Deposition ◽  
Atomic Layer Deposition Method

AbstractPhotovoltaic performance of dye sensitized solar cell (DSSC) was enhanced by 19 and 69 % compared to untreated DSSC by treating the nanoporous titanium dioxide (TiO2) by ultra thin Aluminum oxide (Al2O3) and Hafnium oxide (HfO2) grown by atomic layer deposition method. Activation energy of dark current, obtained from the temperature dependent current-voltage (I-V-T), of the untreated DSSC was 1.03 eV on the other hand the DSSCs with Al2O3 and HfO2 surface treatment showed 1.27 and 1.31 eV respectively. A significant change in the activation energy of dark current, over 0.24 eV for Al2O3 treatment and 0.28 eV in case of HfO2 treatment, suggest that density and activity of surface states on nanoporous TiO2 was suppressed by ALD grown metal oxides to result improved photovoltaic performance. Further the enhanced DSSC performance was confirmed by external quantum efficiency measurement in the wavelength range of 350-750 nm.

Luminescence of II-VI Semiconductor Nanoparticles

2014 ◽  
Vol 222 ◽  
pp. 1-65 ◽  
Author(s):  
B.P. Chandra ◽  
V.K. Chandra ◽  
Piyush Jha
Keyword(s):  
Band Gap ◽  
Data Storage ◽  
Quantum Confinement Effect ◽  
Ultrafine Particle ◽  
Surface States ◽  
Emission Spectra ◽  
Volume Ratio ◽  
Blue Shift ◽  
Band Gap Energy ◽  
Molecular Engineering

Nanoparticle or an ultrafine particle is a small solid whose physical dimension lies between 1 to 100 nanometers. Nanotechnology is the coming revolution in molecular engineering, and therefore, it is curiosity-driven and promising area of technology. The field of nanoscience and nanotechnology is interdisciplinary in nature and being studied by physicists, chemists, material scientists, biologists, engineers, computer scientists, etc. Research in the field of nanoparticles has been triggered by the recent availability of revolutionary instruments and approaches that allow the investigation of material properties with a resolution close to the atomic level. Strongly connected to such technological advances are the pioneering studies that have revealed new physical properties of matter at a level intermediate between atomic/molecular and bulk. Quantum confinement effect modifies the electronic structure of nanoparticles when their sizes become comparable to that of their Bohr excitonic radius. When the particle radius falls below the excitonic Bohr radius, the band gap energy is widened, leading to a blue shift in the band gap emission spectra, etc. On the other hand, the surface states play a more important role in the nanoparticles, due to their large surface-to-volume ratio with a decrease in particle size (surface effects). From the last few years, nanoparticles have been a common material for the development of new cutting-edge applications in communications, energy storage, sensing, data storage, optics, transmission, environmental protection, cosmetics, biology, and medicine due to their important optical, electrical, and magnetic properties.

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