Fast piezoresistive sensor and UV photodetector based on Mn‐doped ZnO nanorods

A low cost hydrothermal synthesis method to synthesize Mn‐doped ZnO nanorods (NRs) with controllable morphology and structure has been developed. Ammonia is used to tailor the ammonium hydroxide concentration, which provides a source of OH^– for hydrolysis and precipitation during the growth instead of HMT. The morphological, chemical composition, structural, and electronic structure studies of the Mn‐doped ZnO NRs show that the Mn‐doped ZnO NRs have a hexagonal wurtzite ZnO structure along the c‐axis and the Mn ions replace the Zn sites in the ZnO NRs matrix without any secondary phase of metallic manganese element and manganese oxides observed. The fabricated PEDOT:PSS/Zn_0.85Mn_0.15O Schottky diode based piezoresistive sensor and UV photodetector shows that the piezoresistive sensor has pressure sensitivity of 0.00617 kPa^–1 for the pressure range from 1 kPa to 20 kP and 0.000180 kPa^–1for the pressure range from 20 kPa to 320 kPa with relatively fast response time of 0.03 s and the UV photodetector has both relatively high responsivity and fast response time of 0.065 A/W and 2.75 s, respectively. The fabricated Schottky diode can be utilized as a very useful human‐friendly interactive electronic device for mass/force sensor or UV photodetector in everyday living life. This developed device is very promising for small‐size, low‐cost and easy‐to‐customize application‐specific requirements. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Novel BeZnO Based Self‐Powered Dual‐Color UV Photodetector Realized via a One‐Step Fabrication Method

In this work, we fabricated a novel BeZnO based dual‐color UV photodetector through a one‐step electron beam evaporation of asymmetric Ti/Au pair. A dual‐phase BeZnO alloy film with dual bandgap of ∼3.5 eV (∼355 nm) and ∼4.6 eV(∼270 nm) was artfully utilized as active layer to realize dual‐color response. This photodetector shows a noticeable photovoltaic characteristic and can be utilized as an excellent self‐powered device. The device exhibits two cut‐off response wavelengths at ∼275 nm and ∼360 nm under zero bias, which are corresponding to UVA and UVC region, respectively. According to the dynamic response spectra under UV radiation, the device presents excellent stability and reproducibility without external power supply. In addition, the device has an ultrafast response speed, with a rise time of ∼35 μs and a decay time of ∼880 μs. Finally, a physical model based on energy band theory is proposed to demonstrate that the self‐powered behavior is attributed to the asymmetric Schottky barrier heights caused by the hole‐trapping process occurred in electrode/BeZnO interface. To the best of our knowledge, this is the first report on BeZnO based self‐powered UV photodetector. Our findings demonstrate a novel and facile route to realize high performance self‐powered UV photodetectors for multipurposes.     

Humidity sensor and ultraviolet photodetector based on carrier trapping effect and negative photoconductivity in graphene quantum dots

We report on the experimental realization of a graphene quantum dots(GQD)-based humidity sensor and ultraviolet(UV)photodetector. We demonstrate that the conductance of the GQD increases linearly with increasing relative humidity(RH) of the surrounding environment due to the carrier trapping effect, which forms the basis of a humidity sensor. When the sensor is operated in the dark state, the sensitivity can reach as high as 0.48 nS RH~(-1). The GQD are also found to exhibit light intensity dependent negative photoconductivity under the UV irradiation, which can be exploited for UV detection. As a result of these carrier trapping and de-trapping processes, the performance of the photodetector can be significantly improved with the increasing RH, and the photoresponsivity can reach a high value of.418.1 μA W~(-1) in the high humid state of RH=90%.     

不同钝化结构对非极性AlGaN-MSM紫外探测器性能的提升

在r面蓝宝石衬底上,采用金属有机化学气相沉积（MOCVD）法高温生长了未掺杂非极性AlGaN半导体薄膜,在此基础上制备了金属-半导体-金属（MSM）结构的紫外探测器。系统研究了在AlGaN半导体薄膜表面分别磁控溅射SiO₂纳米颗粒与SiO₂钝化层两种钝化手段对非极性AlGaN-MSM结构的紫外探测器性能的影响。实验结果表明：磁控溅射SiO₂纳米颗粒钝化或SiO₂钝化层两种手段都能提升AlGaN-MSM结构紫外探测器性能。暗电流测试表明,SiO₂纳米颗粒和SiO₂钝化层可使器件暗电流下降1~2个数量级,达到nA量级。光谱响应测试发现,在5 V偏压下,探测器在300 nm处具有陡峭的截止边,这表明其具有很好的深紫外特性,光谱响应提高了10³倍,紫外可见抑制比高达10⁵。     

The mechanism of photocurrent enhancement of ZnO ultraviolet photodetector by reduced graphene oxide

An ultraviolet (UV) photodetector based on ZnO-reduced graphene oxide (ZnO-rGO) composites have been successfully fabricated. A pure ZnO photodetector was also fabricated by similar method. In comparison with the pure ZnO UV photodetector, the ZnO-rGO photodetector exhibits a much larger photocurrent and a better light-to-dark-current-ratio. The mechanism of photocurrent enhancement was investigated using I-V characteristics, photoluminescence (PL) spectra, transmittance spectra and time-dependent photocurrent analysis. Results show that the photocurrent enhancement of the ultraviolet photodetector is due to the improvement of the carrier lifetime, because the carrier recombination of ZnO were reduced by rGO. It provides a potential way to fabricate high-response UV photodetectors.     

ZnO nanowire array ultraviolet photodetectors with self-powered properties

A ZnO nanowire (NW) array ultraviolet photodetector (PD) with Pt Schottky contacts has been fabricated on a glass substrate. Under UV light illumination, this PD showed a high photo-to-dark current ratio of 892 at 30 V bias. Interestingly, it was also found that this PD had a high sensitivity of 475 without external bias. This phenomenon could be explained by the asymmetric Schottky barrier height (SBH) at the two ends causing different separation efficiency of photogenerated electron–hole pairs, which resulted in the formation of photocurrent. It is anticipated to have potential applications in self-powered UV detection field.     

表面修饰ZnO纳米线紫外光响应的增强效应

制备了基于单根ZnO纳米线的紫外光探测原型器件,并研究了聚苯乙烯硫酸钠表面修饰对器件紫外响应特性的影响.研究发现,在相同的紫外光照射条件下,表面修饰后的器件对紫外光的探测灵敏度比修饰前提高了3个数量级.I-V特性研究表明,修饰前后器件在光照时的电导没有明显变化,但修饰后器件的暗电导却下降了3个数量级.这说明通过表面修饰降低探测器的暗电导是提高紫外光探测器灵敏度的一条重要途径. 关键词： 紫外光探测器 纳米结构 ZnO 表面修饰     

Thermal annealing effects on the dynamic photoresponse properties of Al-doped ZnO nanowires network

In this study, UV photodetectors based on a network of aluminium-doped zinc oxide (AZO) nanowires were manufactured at a low cost; for this purpose, a fast and simple fabrication process that involved dropping nanowires dispersion solution was employed instead of the conventional e-beam lithography process that is used to manufacture single nanowire–based UV photodetectors. It was demonstrated that nanowire network–based UV photodetectors provide a much faster UV photoresponse than conventional single nanowire–based UV photodetectors. The fast UV photoresponse of the fabricated UV photodetector can be attributed to the fact that the potential barriers formed in the nanowire network junctions effectively block the flow of electrons during the process of photocurrent decay. Furthermore, the UV photoresponse under illumination by a 254 nm UV source was studied as a function of the annealing temperature of the AZO nanowires network at a bias of 5 V. The fabricated UV photodetector showed the fastest response of 2 s to UV illumination in air when the sample was annealed in air for 1 h at 300 °C.     

A self-powered β-Ga2O3/CsCu2I3 heterojunction photodiode responding to deep ultraviolet irradiation

In this paper, a lead-free halide perovskite CsCu₂I₃ film with high stability was prepared by the anti-solvent assisted crystallization method. Then, we coupled it with Ga₂O₃ to prepare a corresponding heterojunction deep ultraviolet (UV) photodetector. After testing, we concluded that the photodetector is sensitive to 254 nm UV light. The photodetector has good reproducibility, and has an ultra-high photo-to-dark current ratio (PDCR) of more than 10⁵. In addition, under a bias of 10 V and an illuminated intensity of 200 μW/cm², the responsivity (R) and specific detectivity (D*) reached 20 mA/W and 10⁷ cm Hz^1/2 W⁻¹ (Jones), and the external quantum efficiency (EQE) is 10%. Meanwhile, the prepared photodetector could operate at zero bias, i.e., self-powered operation, along with a photocurrent of about 1 nA under illumination with UV light intensity of 200 μW/cm².     

基于氧化锌纳米颗粒-石墨烯异质结构的高性能紫外光探测器 (cited: 5)

报道了一种基于水热反应制备无表面活性剂的氧化锌纳米颗粒-还原石墨烯异质结构的新方法. 研究表明异质结构中氧化锌纳米晶体颗粒的平均直径为5 nm,这些颗粒均匀分布在还原石墨烯表面,其密度可以通过反应物的浓度进行有效调节. 并进一步构建了基于这种异质结构的光电探测器. 该探测器对紫外光的响应很快,光电流响应变化可达四个量级. 这些结果表明该异质结构特别适合作为替代材料用于设计和构建高性能的紫外光探测器件.     

TiO2 Nanotube Array/Monolayer Graphene Film Schottky Junction Ultraviolet Light Photodetectors

Schottky junctions made from a titanium dioxide nanotube (TiO₂NT) array in contact with a monolayer graphene (MLG) film are fabricated and utilized for UV light detection. The TiO₂NT array is synthesized by the anodization and the MLG through a simple chemical vapor deposition process. Photoconductive analysis shows that the fabricated Schottky junction photodetector (PD) is sensitive to UV light illumination with good stability and reproducibility. The corresponding responsivity (R), photoconductive gain (G), and detectivity (D*) are calculated to be 15 A W^?1, 51, and 1.5 × 10¹² cm Hz^1/2 W^?1, respectively. It is observed that the fabricated PD exhibits spectral sensitivity and a simple power‐law dependence on light intensity. Moreover, the height of the Schottky junction diode is derived to be 0.59 V by using a low temperature I–V measurement. Finally, the working mechanism of the TiO₂NT array/MLG film Schottky junction PD is elucidated.     

Quick-response film photodetector of high-power laser radiation based on the optical rectification effect

The efficiency of conversion of high-power laser radiation to an electric signal based on the optical rectification effect in nanographite films is studied experimentally. The amplitude of the signal is found to significantly depend on the size of the film, as well as on the length and arrangement of measuring electrodes. The maximal sensitivity of the photodetector (above 500 mV/MW at a wavelength of 1064 nm) consisting of the film with electrodes and operating without an external power supply and add-on components is shown to be achieved when the size of the film is comparable to the laser beam diameter. The sensitivity of the photodetector is studied under the condition when a nanosecond beam from a pulsed laser scans the surface of the film in two mutually perpendicular directions. The local sensitivity increases near the free ends of the photodetector. It is shown that the nanographite detector and a similar photodetector made of a polished silicon wafer have radically different parameters.     

Fabrication and performance evaluation of ultraviolet photodetector based on organic /inorganic heterojunction

Organic/inorganic ultraviolet photodetector was fabricated using thermal evaporation technique. Organic/inorganic heterojunction based on thermally evaporated copper (II) acetylacetonate thin film of thickness 200 nm deposited on an n-type silicon substrate is introduced. I–V characteristics of the fabricated heterojunction were investigated under UV illumination of intensity 65 mW/cm². The diode parameters such as ideality factor, n, barrier height, Φ_B, and reverse saturation current, I_s, were determined using thermionic emission theory. The series resistance of the fabricated diode was determined using modified Nord's method. The estimated values of series resistance and barrier height of the diode were about 0.33 KΩ and 0.72 eV, respectively. The fabricated photodetector exhibited a responsivity and specific detectivity about 9 mA/W and 4.6 × 10⁹ Jones, respectively. The response behavior of the fabricated photodetector was analyzed through ON-OFF switching behavior. The estimated values of rise and fall time of the present architecture under UV illumination were about 199 ms and 154 ms, respectively. Finally, enhancing the photoresponsivity of the fabricated photodetector, post-deposition plasma treatment process was employed. A remarkable modification of the device performance was noticed as a result of plasma treatment. These modifications are representative in a decrease of series resistance and an increase of photoresponsivity and specific detectivity. The process of plasma treatment achieved an increment of external quantum efficiency from 5.53% to 8.34% at −3.5 V under UV illumination.     

The simulation of temperature dependence of responsivity and response time for 6H-SiC UV photodetector

In this paper the temperature dependence of responsivity and response time for 6H-SiC ultraviolet (UV) photodetector is simulated based on numerical model in the range from 300K to 900K. The simulation results show that the responsivity and the response time of device are less sensitive to temperature and this kind of UV photodetector has excellent temperature stability. Also the effects of device structure and bias voltage on the responsivity and the response time are presented. The thicker the drift region is, the higher the responsivity and the longer the response time are. So the thickness of drift region has to be carefully designed to make trade-off between responsivity and response time.     

基于石墨烯-钙钛矿量子点场效应晶体管的光电探测器

以等离子增强化学气相沉积法制备的石墨烯作为导电沟道材料,将其与无机CsPbI_3钙钛矿量子点结合,设计并制备了石墨烯-钙钛矿量子点场效应晶体管光电探测器.研究和分析了石墨烯作为场效应晶体管的电学特性及其与钙钛矿量子点结合作为光电探测器的光电特性.结果表明,石墨烯在场效应晶体管中表现出良好的电学性质,其与钙钛矿量子点的结合对波长为400 nm的光辐射具有明显的光响应,在光强为12μW时器件光生电流最大为64μA,响应率达6.4 A·W~(-1),对应的光电导增益和探测率分别为3.7×10~4,6×10~7Jones(1 Jones=1 cm·Hz~(1/2)·W~(-1)).     

n-ZnO/LaAlO3/p-Si heterojunction for visible-blind UV detection

A visible-blind UV photodetector (PD) using a double heterojunction of n-ZnO/LaAlO3 (LAO)/p-Si was demonstrated. Inserted LAO layers exhibit electrical insulating properties and serve as blocking layers for photoexcited electrons from p-Si to n-ZnO, leading to an enhanced rectification ratio and a visible-blind UV detectivity of the n-ZnO/LAO/p-Si PDs due to the high potential barrier between LAO and p-Si layers (~2.0 eV). These results support the use of n-ZnO/LAO/p-Si PDs in the visible-blind UV PDs in a visible-light environment.     

Field emission graphene–oxide–silicon field effect based photodetector

Silicon‐based devices keep moving into smaller dimension for improving the speed, efficiency, and low‐power consumption. Novel designed semiconductor device architectures are needed to overcome the physical limitations. An integration of well‐designed nanostructure and nanomaterials can potentially establish new principles and approaches to nanoelectronic and photonic devices. We herein demonstrate a graphene/SiO₂/p‐Si (GOS) heterostructure with an embedded nanoscale mesa, forming a GOS‐Mesa field‐effect photodetector. The proposed structure exhibits that multiple exciton generation (MEG) can occur in a quantum‐confined two‐dimensional electron gas (2DEG) region via impact ionization, leading to high internal quantum efficiency (η_IQE). The numerical simulation of the carrier multiplication (CM) factor in our designed structure finds a reasonable agreement with empirical data. Simulated and measured internal quantum efficiency demonstrate ～195% and ～135% of UV–Vis radiation, respectively. A vertically confined 2DEG plays an important role not only in enabling the electron emission process which is responsible for the flowing of electron current, but also in developing a highly localized electric field (up to ～10⁶ V/cm) at the SiO₂/Si interface, enabling an impact ionization process under photon energy of merely ～1.95 eV. Our findings demonstrate that carrier multiplication can be achieved in a suitably designed nanoscale structure in conjunction with nanomaterial on silicon‐based devices, providing incentive to better understand MEG within quantum wells in 2DEG systems, and being a research path to enhancing the efficiency of future solar harvesting technologies. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

4H-SiC-based photodetector of Carcinogenic UV radiation

Carcinogenic (bactericidal) radiation (200–300 nm with a peak at 254 nm) is present in natural (Sun) and artificial (lamps) source of UV radiation. Its intensity is very low as compared to other types of radiation, but it strongly affects the health of human beings. To prevent oncological diseases, it is important to monitor the carcinogenic radiation level; i.e., selective photodetectors are required. A UV photodetector based on n-4H-SiC Schottly barriers and the p ⁺-n junction is proposed. The quantum efficiency spectrum of such detectors is very close to the spectrum of relative action of carcinogenic radiation on human beings. The quantum efficiency (at the spectral peak (254 nm) amounts to about 0.3 electrons/photon for virtually zero sensitivity in other spectral regions. Quantum efficiency in the wavelength range 247–254 nm is practically independent of temperature in the range from ?100 to +100°C.     

The fabrication and characterization of ZnO UV detector

ZnO films were deposited on GaAs substrates by radio frequency (rf) magnetron sputtering followed by an ambient-controlled heat treatment process for arsenic doping. In Hall measurements, the As-doped ZnO films showed the characteristics of p-type semiconductor. The ZnO thin film p–n homojuctions were then fabricated to investigate the electrical properties of the films. The p–n homojunctions exhibited the distinct rectifying current–voltage (I–V) characteristics. The turn-on voltage was measured to be 3.0 V under the forward bias. When ultraviolet (UV) light (λ = 325 nm) was irradiated on the p–n homojunction, photocurrent of 2 mA was detected. Based on these results, it is proposed that the p–n homojunction herein is a potential candidate for UV photodetector and optical devices.     

Pseudo 2-transistor active pixel sensor using an n-well/gate-tied p-channel metal oxide semiconductor field eeffect transistor-type photodetector with built-in transfer gate

In this paper, a pseudo 2-transistor active pixel sensor (APS) has been designed and fabricated by using an n-well/gate-tied p-channel metal oxide semiconductor field effect transistor (PMOSFET)-type photodetector with built-in transfer gate. The proposed sensor has been fabricated using a 0.35 μm 2-poly 4-metal standard complementary metal oxide semiconductor (CMOS) logic process. The pseudo 2-transistor APS consists of two NMOSFETs and one photodetector which can amplify the generated photocurrent. The area of the pseudo 2-transistor APS is 7.1 × 6.2 μm². The sensitivity of the proposed pixel is 49 lux/(V·s). By using this pixel, a smaller pixel area and a higher level of sensitivity can be realized when compared with a conventional 3-transistor APS which uses a pn junction photodiode.