Photoresponse Measurements Research Articles

Improved Process Stability and Light Detection in Phototransistors via Inverted MoS2/a‐IGZO Heterojunction Integration

The integration of molybdenum disulfide (MoS2) with other semiconductors to form heterojunction phototransistors demonstrates potential for optoelectronic applications due to their strong interaction with light and tunable bandgaps. Conventionally, bottom‐gate phototransistors based on MoS2 and amorphous indium–gallium–zinc oxide (a‐IGZO) are fabricated by deposition of the a‐IGZO film on the gate dielectric, followed by deposition of the MoS2 film, resulting in a MoS2/a‐IGZO heterojunction. In this study, an inverted MoS2/a‐IGZO (or denoted as a‐IGZO/MoS2) heterojunction integration for bottom‐gate phototransistors, where the MoS2 film is deposited on the gate dielectric first, followed by the deposition of the a‐IGZO film, is presented. This configuration is designed to enhance the processability and electrical properties of the phototransistor. Under visible light exposure with a low optical power density of 5.3 μW cm−2, the a‐IGZO/MoS2 heterojunction phototransistor demonstrates significantly improved photoresponsivity (1.6, 2.8, and 17 A W−1 at 635, 520, and 405 nm wavelengths, respectively) compared to the MoS2 single‐channel phototransistor. Time‐dependent photoresponse measurements reveal that the a‐IGZO/MoS2 heterojunction phototransistor responds more quickly to light changes and generates a tenfold‐greater photocurrent than that of the MoS2 single‐channel phototransistor.

High-performance transparent AZO UV photodetectors

In this work, the fabrication of undoped ZnO (ZO) and 3 at.% aluminum (Al) doped ZnO (AZO) thin films (TFs) based transparent photodetectors (PDs) was reported. Both films were spin-coated on fluorine-doped tin oxide (FTO) substrates to investigate the influence of Al doping on the ultraviolet (UV) detection performance of the devices. The systematic characterizations reveal that Al doping positively affects the characteristics of ZO-TFs. The Al doping leads to slight shift in crystalline peaks and induces an enhancement in grain size. In addition, the surface roughness of ZO-TFs gets lower on Al doping. Further, the Al doping improved the transparency and widening of band gap of TFs. The PDs having metal–semiconductor-metal (MSM) configuration were achieved by screen-printing of Ag paste onto ZO and AZO-TFs. The current–voltage (I-V) profiles of the fabricated PDs were measured in the dark and under UV excitation of 365 nm. The AZO-TFs based MSM PD exhibits a spectral responsivity of 326.82 mA/W and an external quantum efficiency of 111.03%. The reproducibility of the fabricated PDs was tested by performing time-dependent photo-response measurements.

Significantly enhanced photo response of hydrazine hydrate reduced graphene oxide films modified with swift heavy ion irradiation of silver (Ag8+) ions

In this paper, a multistep reduction process of graphene oxide (GO) is discussed. It is basically a two-step reduction process. In the first step, the GO sample is reduced by hydrazine hydrate. In the second step, it is further reduced by a swift heavy ion irradiation beam of silver (Ag8+) ions of 100 MeV energies. Ion beam irradiation causes defects in the hydrazine hydrate reduced graphene oxide (rGO) samples. FTIR study confirms the removal of oxygen containing functional groups. The pore volume and pore density of the samples seem to increase with increase in the ion irradiation doses. It is also seen that the electrical conductivity and specific surface area increases with dose of ion irradiation. The prepared samples were tested for photo response measurement and among all the sample, R5 had the highest photo response of 6.25 % at 30 mW/cm2. The photodetection response seems to increase with increase in intensity of light.

Photoresponse in sequentially stacked antimony selenide thin films

Antimony selenide (Sb2Se3), a binary semiconducting compound has widespread research attention due to its excellent optoelectronic properties in the visible region and usefulness in applications such as solar cells, photosensors and photoelectrodes. The presented study explores the thickness dependent photoresponse in Sb2Se3 thin films, prepared by reactive selenization of antimony films having thickness values of ∼938 nm and ∼1879 nm when stacked second time. Growth orientation along [001] direction was achieved through carefully optimized selenization conditions to enable favourable charge transport in anisotropic Sb2Se3. Predominant Sb2Se3 formation was inferred from x-ray diffraction, Raman spectroscopy, secondary electron microscopy and energy-dispersive X-ray analyses. High optical absorption coefficient values of about 1 × 105 cm−1 and 5.7 × 104 cm−1 were observed for ∼938 nm and ∼1879 nm thick Sb2Se3 thin films. Further, the optoelectronic properties were elucidated through current–voltage and transient photoresponse measurements under dark and illumination conditions. The measurements were done under zero and different bias voltages. Sb2Se3 films having∼ 938 nm thickness exhibited self-driven photoresponse with a responsivity of 4.3×10−8 A W−1 and detectivity of 3.5 × 106 jones respectively, under AM 1.5 G illumination conditions.

Large area MoSe2 and MoSe2/Bi2Se3 films on sapphire (0001) for near-infrared photodetection

The fabrication of heterojunction-based photodetectors (PDs) is well known for the enhancement of PDs performances, tunable nature of photoconductivity, and broadband application. Herein, the PDs based on MoSe2 and MoSe2/Bi2Se3 heterojunction on sapphire (0001) substrates were deposited using a r.f. magnetron sputtering system. The high-resolution x-ray diffraction and Raman spectroscopy characterizations disclosed the growth of the 2-H phase of MoSe2 and the rhombohedral phase of Bi2Se3 thin films on sapphire (0001). The chemical and electronic states of deposited films were studied using x-ray photoelectron spectroscopy and revealed the stoichiometry growth of MoSe2. We have fabricated metal-semiconductor–metal type PD devices on MoSe2 and MoSe2/Bi2Se3 heterojunction and the photo-response measurements were performed at external voltages of 0.1–5 V under near-infrared (1064 nm) light illumination. The bare MoSe2 PD device shows positive photoconductivity behavior whereas MoSe2/Bi2Se3 heterojunction PD exhibits negative photoconductivity. It was found that the responsivity of MoSe2 and MoSe2/Bi2Se3 heterojunction PDs is ~ 1.39 A W−1 and ~ 5.7 A W−1, respectively. The enhancement of photoresponse of MoSe2/Bi2Se3 PD nearly four-fold compared to bare MoSe2 PD shows the importance of heterojunction structures for futuristics optoelectronic applications.

Photoelectrical characterization of heavily doped p-SiC Schottky contacts

The availability of photoelectrical characterizations of heavily Al-doped p-SiC Schottky contacts was clarified. We conducted a systematic study of four samples with different Al doping concentrations from 1 × 1018 to 5 × 1019 cm−3. Although the current–voltage (I–V) characteristics had lost rectification, reasonable Schottky barrier height (qϕ B) values were obtained up to 1 × 1019 cm−3 by capacitance voltage, photo response, and scanning internal photoemission microscopy (SIPM) measurements. In the two-dimensional characterization by SIPM, large photocurrent spots corresponding with low qϕ B were observed in an average density of 103 to 104 cm−2. However, except for these spots, a high uniformity of about 2 meV standard deviation was obtained for qϕ B over the entire observed electrodes. These results indicate that SIPM is able to characterize the inhomogeneity of heavily doped p-SiC contacts with very leaky I–V characteristics.

High-performance terahertz modulators induced by substrate field in Te-based all-2D heterojunctions

High-performance active terahertz modulators as the indispensable core components are of great importance for the next generation communication technology. However, they currently suffer from the tradeoff between modulation depth and speed. Here, we introduce two-dimensional (2D) tellurium (Te) nanofilms with the unique structure as a new class of optically controlled terahertz modulators and demonstrate their integrated heterojunctions can successfully improve the device performances to the optimal and applicable levels among the existing all-2D broadband modulators. Further photoresponse measurements confirm the significant impact of the stacking order. We first clarify the direction of the substrate-induced electric field through first-principles calculations and uncover the unusual interaction mechanism in the photoexcited carrier dynamics associated with the charge transfer and interlayer exciton recombination. This advances the fundamental and applicative research of Te nanomaterials in high-performance terahertz optoelectronics.

Chemical bath deposition-based synthesis of tin sulfide on silicon substrate and its application as a photodetector

Tin sulfide (SnS) is an attractive compound semiconductor for photovoltaic and sensing applications because of its abundance and non-toxicity. In the present work, the synthesis of SnS thin films on silicon substrates by chemical bath deposition (CBD) technique has been demonstrated. Tin chloride (SnCl2.2H2O) and thiourea were used as the tin and sulfur sources to deposit the SnS films with triethanolamine (TEA) as the complexing agent and sodium hydroxide (NaOH) as alkaline bath. To understand the growth mechanism, a time interrupted growth series was adopted at a temperature of 90 °C for different time durations i.e., 60 min, 120 min, and 180 min. A photosensor was fabricated using the SnS/Si heterojunction and its performance was investigated through electrical (current-voltage) and optical (photo-response) measurements. The I–V characteristics of the developed photodetector were recorded under dark and different light intensities. The device exhibited significant response to light even without a bias voltage.

Optoelectronic enhancement of ZnO/p-Si Schottky barrier photodiodes by (Sn,Ti) co-doping

In this study, metal–semiconductor–metal (MSM) ZnO-based Schottky barrier diodes (SBDs) were fabricated on the basis of titanium-doped tin–zinc oxide (SZT) films by sol–gel spin coating. Au/(Sn:Zn):Ti:ZnO/p-Si/Au SBDs with varying wt% of Ti were then fabricated. The effects of Ti doping concentration on the structural, optical, and electrical properties were studied. The doped films are consistently homogeneous with increasing Ti content. The optical measurements confirm high film transmittance in the visible spectrum. The optical band gap energy of the SZT films was around 3.90 ± 0.02 eV. The current–voltage, impedance spectroscopic, and photoresponse measurements showed that Ti-doping improved the performance of the devices by increasing the barrier heights and hence the rectification ratios of the devices. The reduction in ideality factors and series resistances implies that Ti doping improves the devices towards near-ideal behavior by passivating interface states.

Nanostructures arrayed broad spectrum-based rigid and flexible photodetectors with selective detection

High-performance one-dimensional (1D) CdSxSe1−x nanostructures arrayed photodetectors exhibit broad spectrum (450–750 nm) selective detection from the near-ultraviolet to the near-infrared regime, which has a great deal of interest in broad spectral flexible optoelectronic devices. Here, we report the microstamp transfer technology to construct high-performance rigid (SiO2/Si) and flexible (polyethylene terephthalate) photodetectors with broad spectrum selective detection, which was based on arrayed 1D CdSxSe1−x nanostructures obtained via chemical vapor deposition in a dual-temperature zone tube furnace. Photoresponse measurements have demonstrated their superior spectral photoresponsivity (∼105 AW−1), extremely high on/off switching ratio (105), rapid response/recovery time between 10% and 90% of the maximum photocurrent (0.089/0.044, 0.044/0.044, 0.133/0.131, and 0.178/0.180 s), and excellent long-term environmental photostability. Furthermore, the as-prepared flexible arrayed photodetector displayed excellent folding endurance properties (after 2000 times, the photocurrent decreases less than 50%) and stable electrical properties (bending angle from 0° to 150°). The improvement nanoarray technology in this research can be exploited to lead to the design of high-performance flexible photodevices comprising other 1D or 2D alloy nanomaterials.

Capillary‐Assisted Self‐Assembly of Carbon Nanotubes for the Self‐Powered Photothermoelectric Detector

The development of mid‐infrared (MIR) detectors has become a hot research topic with significant progress in low‐dimensional materials and clean‐room fabrication strategies. Some of the applications of MIR detectors include industrial non‐destructive testing, wearable safety monitoring, and other Internet of Things. Photothermoelectric (PTE) mechanism, as a room‐temperature free‐bias conversion mode, is comprehensively developed in the MIR regimes in the last decade. Although carbon nanotubes (CNTs) and their related materials are demonstrated as effective PTE conversion materials, the large‐area scalable detector fabrication based on the Si substrate is still underdeveloped, thus limiting further PTE device designs and industrial applications. Herein, the self‐assembly CNT‐based detectors driven by the capillary force are fabricated to achieve sensitive and rapid IR detection, and photoresponse measurements of PTE detectors are experimentally performed at room temperature and atmospheric conditions. This work reveals that the PTE mechanism can play a key role in the IR response, thereby broadening horizons about high‐performance IR detectors in industrial applications.

Photoresponse of Solution-Synthesized Graphene Nanoribbon Heterojunctions on Diamond Indicating Phototunable Photodiode Polarity

Graphene nanoribbon heterostructures and heterojunctions have attracted interest as next-generation molecular diodes with atomic precision. Their mass production via solution methods and prototypical device integration remains to be explored. Here, the bottom-up solution synthesis and characterization of liquid-phase-processable graphene nanoribbon heterostructures (GNRHs) are demonstrated. Joint photoresponsivity measurements and simulations provide evidence of the structurally defined heterostructure motif acting as a type-I heterojunction. Real-time, time-dependent density functional tight-binding simulations further reveal that the photocurrent polarity can be tuned at different excitation wavelengths. Our results introduce liquid-phase-processable, self-assembled heterojunctions for the development of nanoscale diode circuitry and adaptive hardware.

An investigation into the hybrid architecture of Mn-Co nanoferrites incorporated into a polyaniline matrix for photoresponse studies.

In this study, an enhanced photoresponse was observed in the Mn-Co Nanoferrites (MCFs)-Polyaniline (PANI) nanohybrid architecture due to the formation of interface between PANI and MCFs, which provided a conduction pathway for the movement of charge carriers, and these interfaces were observed in a high-resolution transmission electron micrograph (HR-TEM). X-ray photoelectron spectroscopy (XPS) suggests that the carbon (C 1s) of the MCF-PANI nanohybrid shows peaks at 287.80 eV for CO, 286.17 eV for C-O, 285.24 eV for C-N, 284.50 eV for the sp3 hybridized carbon (C-C/C-H) and 283.84 eV for the sp2 hybridized carbon (CC). Current-voltage (I-V) curves reveal an ohmic nature of the MCF-PANI nanohybrid photodetector device. The photoresponse measurements were analyzed using the trap depth concept, demonstrating that the conductive polymer increases the photoconduction mechanism efficiency of MCFs. The constructed photodetector device exhibits a high photoresponsivity of 22.69 A W-1, a remarkable detectivity of 1.36 × 1012 cm Hz1/2 W-1 and a fast rise/decay time of 0.7/0.8 s. The excellent performance of the as-fabricated photodetector device could be explained by the intimate interaction between MCFs and PANI at their interface.

Ultraviolet and visible photo-response of transparent conductive Al-doped ZnO (AZO)/n-Silicon isotype heterojunction device

In this work, the electrical and photoresponse measurements of a transparent conductive Al-doped ZnO (AZO)/n-Si heterojunction device were conducted in visible light and UV wavelengths. AZO film was deposited by sputtering onto an n-Si wafer and investigated by means of morphological, chemical and electrical characterizations. The AZO/n-Si rectifying device exhibits an excellent reproducibility without noticeable variations after 90 days of measurements. At self-powered mode, the maximum on/off ratios were determined as 3081 for visible light and 4778 for UV light illumination of 365 nm. The responsivity and detectivity of the AZO/n-Si photodetector were 0.128 A W−1 and 1.05 × 1011 Jones for 365 nm, whereas they were 0.055 A W−1 and 4.60 × 1010 Jones for 395 nm, respectively (at −2.0 V). This study demonstrated that the n-AZO/n-Si isotype heterojunction photodetector was fabricated at low cost and it is a potential candidate in both the visible region and the UV region with a good performance, in contrast to the widely studied pn heterojunctions.

In-depth investigation of low-energy proton irradiation effect on the structural and photoresponse properties of ε-Ga2O3 thin films

Ga2O3 possesses an ultra-wide bandgap (∼4.9 eV) and an extremely large breakdown field strength (∼8 MV/cm), which promises extraordinary application potential in power electronics and ultraviolet optoelectronics. With the demand for highly durable devices in harsh environments such as in low earth orbit spacecraft, in-depth understanding of the particle radiation effect on the structural and performance degradation of the device is desired. In this work, we employ 150 keV low energy proton with intensity up to 5 × 1015 dose to irradiate the epitaxial ε-Ga2O3 thin films. The characterization of the structural and optical properties shows no detectable variations in lattice structure and optical transmission. In addition, with increasing irradiation dosage, a decrease of Ga3+ population and an increase of the concentration of oxygen vacancies are confirmed by X-ray photoemission spectroscopy. Photoresponse measurements further illustrate that, despite of a mild degradation in the photodetector performance, the device still shows a high photoresponsivity of 2.52 × 10-3 A/W and a large photo-to-dark current ratio over 103. Our work reveals that ε-Ga2O3 exhibits excellent radiation hardness under low-energy proton irradiation conditions and highlights the potential for operational optoelectronics in extreme environment.

Preparation and Characterization of CdS and PbS Chalcogenides Compounds and n-CdS/p-PbS photodiode

In this study, a chemical bath deposition method (CBD) is used to synthesize CdS nanocrystalline thin films onto FTO substrate using two temperatures of 70 and 80 ºC for 1h of preparation time. PbS nanocrystalline thin films are also prepared using CBD using temperature of 35 ºC for 2h. XRD measurements confirmed that the prepared CdS and PbS thin films are polycrystalline with hexagonal phase for CdS and cubic for PbS. Scanning Electron Microscope images show increasing particles size of CdS thin films with increasing temperature of preparation and the films became more adherent on the substrates without pinholes or vacancies. Optical properties are investigated through UV-Visible Spectroscopy and found decreasing in the transmittance of prepared thin films with increasing temperature. Energy band gap calculated for CdS and PbS nanocrystalline thin films found with values higher than bulk value indicating to due to the quantum confinement effect. Photoluminescence spectra of prepared CdS nanocrystalline thin films appeared sharp emission beak at around 550 nm for all samples indicating high crystallinity. Photoresponse measurements of the fabricated photodetector showed a significant sensitivity to visible light at zero applied voltage, indicating that the fabricated device is a self-powered photodetector. The device was highly photosensitive of 16833, responsivity of 1.44 mAW−1, and a low rise/fall time of 0.284/0.298 s.

Highly-detective tunable band-selective photodetector based on RF sputtered amorphous SiC thin-film: Effect of sputtering power

In this paper, a new high-performance tunable band-selective (UV-Visible) photodetector (PD) based on RF sputtered a-SiC active layer is demonstrated. SiC thin-films were deposited on glass substrate by RF magnetron sputtering method at different sputter power values ranging from 60 W to 120 W. The samples morphological, structural, optical and photodetection properties were investigated by carrying out XRD, SEM, EDS, UV-Vis spectroscopy and photoresponse measurements. It was revealed that the sputtering power could modulate the optical behavior of a-SiC alloy, tuning favorable visible absorbance at high sputter power. This phenomenon is correlated with the influence of the RF power on the SiC film structural properties and compositions. Interestingly, measurements showed that a-SiC PD elaborated at 60 W of RF power can detect UV radiation with a high responsivity of 138 mA/W, low noise effects, superior detectivity of 7.8 × 10 12 Jones, while maintaining the visible blindness property. On the other hand, the prepared device at high sputtering power exhibits extended photoresponse characteristics, yielding 426 mA/W and 77 mA/W of responsivity values over UV and visible ranges, respectively. Therefore, the present investigation can provide a new strategy for the design and fabrication of photodetector devices based on SiC platform with broadband and solar-blind adjustable sensing purposes according to the desired application. • A new tunable band-selective photodetector based on RF sputtered amorphous SiC alloy was developed. • The effect of sputtering power on the device characteristics was systematically studied. • Structural, Optical and electrical properties were investigated. • High responsivity and detectivity exceeding 138 mA/W and 7 × 10 12 Jones, respectively, are recorded.

Fast Wafer-Level Characterization of Silicon Photodetectors by Photoluminescence Imaging

Photoluminescence imaging (PLI) technique is conventionally used in silicon (Si) photovoltaics (PV) for device characterization and inline quality control, providing substantial assistance for a wafer-level process monitoring from as-cut wafers to fully fabricated devices. Surprisingly, employing this method has not spread outside PV, and thus, its potential remains largely unknown in other fields. In this case study, a fully processed Si photodetector wafer, consisting of photodiodes with various sizes, has been chosen as an example to explore the potential of PLI beyond PV. First, we show that the standard PLI measurement is able to provide a high-resolution full-wafer luminescence image of the complete devices only within a couple of seconds. The image reveals various types of inhomogeneities present in the devices, such as furnace contamination and other processing-induced defects. The measured data are then converted to an effective lifetime image followed by benchmarking with a conventionally measured recombination lifetime map obtained by microwave-detected photoconductance decay (<inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-PCD), demonstrating further superiority of PLI in terms of the spatial resolution and the measurement time. Finally, correlation with diode leakage current and photoresponse measurements show that PLI is able to provide useful information on the final device performance without a need for traditional electrical contact measurements. While this study has focused on Si photodetectors, the results imply that PLI also has potential in other semiconductor devices for fast wafer-level process monitoring purposes as well as for a single device characterization either before or after wafer dicing.

High-Performance and Broadband Flexible Photodetectors Employing Multicomponent Alloyed 1D CdSxSe1-x Micro-Nanostructures.

Low-cost multicomponent alloyed one-dimensional (1D) semiconductors exhibit broadband absorption from the ultraviolet to the near-infrared regime, which has attracted a great deal of interest in high-performance flexible optoelectronic devices. Here, we report the facile one-step fabrication of high-performance broadband rigid and flexible photodevices based on multicomponent alloyed 1D cadmium-sulfur-selenide (CdSxSe1-x) micro-nanostructures obtained via a vapor transport route. Photoresponse measurements have demonstrated their superior spectral photoresponsivity (5.8 × 104 A/W), several orders of magnitude higher than the pristine CdSe nanobelt photodevice, high specific detectivity (2 × 1015 Jones), photogain (1.2 × 105), external quantum efficiency (EQE, 1.4 × 107%), rapid response speed (13 ms), and excellent long-term environmental stability. The multicomponent alloyed CdSxSe1-x nanobelt photodevice demonstrated about three times higher photocurrent as well as can operate under multiple color illuminations (200-800 nm) and at a high applied bias of 10 V with the photoresponsivity and EQE being boosted to 4.34 × 105 A/W and 8.96 × 107%, respectively. Furthermore, multicomponent alloyed CdSxSe1-x nanobelt flexible photodevices show excellent mechanical and flexural photostabilities with identical photoresponse as rigid nanodevices. The improvement mechanism found in the present research can be exploited to lead to the design of high-performance flexible photodevices comprising other multicomponent nanomaterials.

The role of p-GaN layer thickness for the evaluation of high-performance and ultrafast GaInN/GaN multiple quantum wells UV photodetectors

To improve the performance of GaInN/GaN multiple quantum wells (MQW) ultraviolet photodetectors (UV-PDs), the thickness of p-GaN layer plays an important role. Thereby, to see the impact of p-GaN layer thickness on epilayer quality and device performances, in the present work, we fabricated two different sets of GaInN/GaN MQW-based UV-PDs by varying the thickness of p-GaN layer and examined their epilayer quality and device performances by employing various adequate measurements. Due to increase of p-GaN layer thickness from 125 nm (PD1) to 250 nm (PD2), the density of threading dislocations increases which in turn declines the photocurrent (Ip) and hence, the external quantum efficiency (EQE) in the higher excitation regime (<372 nm). On the other hand, above 372 nm, the values of Ip and EQE in PD2 are higher compared to PD1, indicating the length of photo-absorption layer is improved. Interestingly, PD2 exhibits the widening of the spectral sensitivity towards the higher wavelength regime. Moreover, the temporal photo-response measurements at different optical powers, bias voltages, and switching frequencies (wavelength of the light source = 385 nm) reveal that PD2 has relatively better performance over PD1. These results imply that the separation of photoexcited electron-hole pairs is easier in PD2 than PD1. The faster carrier separation process in PD2 is ascribed to the exacerbated built-in potential in the heterojunction as confirmed via capacitance-voltage analysis. Finally, current–voltage measurements suggest that the series resistance in PD2 increases due to increase of total film thickness.