Heterojunction Ultraviolet Photodetector Research Articles

Enhanced Photoresponse Performance of Self‐Powered PTAA/GaN Microwire Heterojunction Ultraviolet Photodetector Based on Piezo‐Phototronic Effect

AbstractThe development of self‐powered high‐performance UV photodetectors is essential for energy efficient futuristic wearable and portable applications. Herein, a self‐powered organic/inorganic (PTAA/GaN microwire) hybrid heterojunction ultraviolet (UV) photodetector (PD) has been prepared by a low‐cost and simple spin‐coating method. Furthermore, the piezo‐phototronic effect as an effective interfacial regulating strategy is utilized to modulate the photo‐response performances of the PD by engineering the energy‐band structure at the local junction/interface. Under 325 nm laser irradiation, the obtained device demonstrates excellent photo‐response properties at 0 V bias, showing a high responsivity (268 mA W−1) and detectivity (2.49 × 1012 Jones) under weak light intensity as low as 0.2 mW cm−2, as well as fast response speeds (rise time of 14 ms and decay time of 23 ms). The PD exhibits better performance than most reported organic/inorganic heterojunction self‐powered PDs. By applying a −0.52% compressive strain, the responsivity and detectivity of the device are greatly enhanced by 32% without external bias, and by 1256% at 2 V bias under 1.4 mW cm−2 light intensity. On the contrary, by applying a 0.41% tensile strain, the responsivity and detectivity are decreased by 18% without external bias. It indicates that the strain has a significant modulating effect on the photo‐response performance of the PD. The positive piezo‐potential modulated energy‐band structure at the PTAA/GaN interface may account for the enhanced performance. This study demonstrates a promising approach to optimize the performance of a self‐powered heterostructure optoelectronic devices through strain modulated.

Enhancing the self-powered performance in VOx/Ga2O3 heterojunction ultraviolet photodetector by hole-transport engineering

As the carrier behavior is crucial to the photoelectric conversion process, the charge-carrier engineering could provide feasible strategy for high-performance photodetector (PD). Herein, self-powered ultraviolet PDs were constructed on VOx/Ga2O3 (VGO) heterojunctions by adopting the solution processed VOx films as hole transport layer (HTL). Treated with different annealing ambients, the HTL demonstrated changeable conductivities due to the regulated crystallinities, phase structures and chemical valences, which further exerted influences on the VGO PDs inducing controllable photodetection properties. With effective hole transportation, low valence band barrier and large built-in field, the modulated VGO PDs achieved enhanced self-powered photodetection performance with photo-to-dark current ratio of 1.08 × 108, on/off ratio of 1.23 × 106, rejection ration (R245/R400) of 3.12 × 104, responsivity of 28.9 mA/W and detectivity of 1.13 × 1014 Jones as well as rise/decay time of 57/74 ms. In consideration of the carrier-transport problems are commonly ubiquitous and particularly vital, our proposed HTL engineering method could open the high-performance route for self-powered ultraviolet PDs.

Performance enhancement of a self-biased n-ZnO microwire/p-GaN heterojunction ultraviolet photodetector incorporating Ag nanowires

Performance of a self-biased n-ZnO MW/p-GaN heterojunction ultraviolet photodetector was enhanced by incorporating Ag nanowires.

A porous GaN/MoO3 heterojunction for filter-free, ultra-narrowband ultraviolet photodetection

A porous GaN/MoO3 heterojunction ultraviolet photodetector with visible-blind, filter-free and ultra-narrowband (FWHM <10 nm) response is presented. This narrowband ultraviolet photodetector is promising for secure communication applications.

Self-powered heterojunction ultraviolet photodetector based on NiO nanosheets/TiO2 nanorods

The heterojunction ultraviolet photodetectors (UV PDs) were fabricated by growing NiO nanosheets on TiO2 nanorod arrays (NRs) via hydrothermal method and their UV photoresponse properties were examined. The crystal structure, and optical properties of heterojunction were characterized by X-ray diffraction (XRD), Raman, absorption and photoluminescence (PL) spectra. The results of X-ray photoelectron spectroscopy (XPS) valence band (VB) spectrum, Mott–Schottky (M–S) curves and electrochemical impedance spectroscopy (EIS) of heterojunctions reveal the separation and transfer of photo-generated carriers in heterojunction interface. The UV PDs exhibit a large responsivity of 0.54 A/W and a high detection sensitivity of 6.0 × 1012 Jones under 365 nm UV illumination at zero bias.

Influence of electrode materials (Ag, Au) on NiO/TiO2 heterojunction UV photodetectors

Ag and Au are typical electrode materials for NiO/TiO2 heterojunction ultraviolet photodetectors (UV PDs), but the influence of work functions of Ag and Au on performance of devices has not been investigated. We synthesized TiO2 NRs on FTO by hydrothermal method and then constructed heterojunction by preparing NiO nanoflakes on TiO2 NRs using chemical bath deposition (CBD) method. The devices with Ag and Au as top electrode show self-power UV response. The energy band information of NiO is determined by X-ray photoelectron spectroscopy (XPS) valence band spectra, absorption spectrum, and work functions obtained by Kelvin probe. Due to the different arrangement between Fermi energy level of NiO and work functions of Ag and Au, the downward and upward band bending is formed in interfaces of Ag/NiO and Au/NiO. The suitable bending of energy band in Au/NiO leads to more favorable hole collection than that of Ag/NiO, which results in higher responsivity of Au/NiO/TiO2/FTO UV PDs.

Graphene Quantum Dot-Sensitized ZnO-Nanorod/GaN-Nanotower Heterostructure-Based High-Performance UV Photodetectors.

The fabrication of a superior-performance ultraviolet (UV) photodetector utilizing graphene quantum dots (GQDs) as a sensitization agent on a ZnO-nanorod/GaN-nanotower heterostructure has been realized. GQD sensitization displays substantial impact on the electrical as well as the optical performance of a heterojunction UV photodetector. The GQD sensitization stimulates charge carriers in both ZnO and GaN and allows energy band alignment, which is realized by a spontaneous time-correlated transient response. The fabricated device demonstrates an excellent responsivity of 3.2 × 103 A/W at -6 V and displays an enhancement of ∼265% compared to its bare counterpart. In addition, the fabricated heterostructure UV photodetector exhibits a very high external quantum efficiency of 1.2 × 106%, better switching speed, and signal detection capability as low as ∼50 fW.

Improving the photoelectrical characteristics of self-powered p-GaN film/n-ZnO nanowires heterojunction ultraviolet photodetectors through gallium and indium co-doping

ZnO, Ga-doped ZnO (GZO), In-doped ZnO (IZO), and Ga–In co-doped ZnO (GIZO) nanowire arrays were grown on a template of sapphire/p-GaN thin film by low-temperature hydrothermal method for fabricating self-powered p-GaN/n-ZnO heterojunction ultraviolet (UV) photodetectors. The authors investigated the effects of Ga or In single doping and Ga–In co-doping on the microstructural features and optical properties of hydrothermally synthesized ZnO nanowires and conducted a comparison study on the photosensing characteristics and photoelectrical response performances of four kinds of p-n heterojunction UV photodetectors. X-ray diffraction (XRD) examination showed that the as-synthesized ZnO-based nanowire arrays had a single-phase hexagonal wurtzite structure and exhibited a preferential orientation along the (002) plane. Scanning electron microscope (SEM) observation evidenced that the type of dopants modified the morphology and average diameter of the nanowires. The average diameter of ZnO-based nanowires was in the range of 61–101 nm. Room-temperature photoluminescence (PL) spectra revealed that these as-synthesized ZnO-based nanowires had high crystalline quality. The current-voltage (I–V) curves of heterojunction photodetectors based on p-GaN thin film/n-ZnO based nanowire arrays exhibited a rectification characteristic in darkness and under UV illumination. Under UV illumination, the GIZO device had the best photosensing characteristics of all the devices under 5 V bias. The light-to-dark current ratio was close to 6.0 at 5 V bias and the turn-on voltage was lower than 1.8 V. The presented p-GaN/n-GIZO heterojunction UV photodetector realized superior photoresponse performance at zero-bias voltage as compared to single-doped and un-doped ZnO devices.

Recent Progress of Heterojunction Ultraviolet Photodetectors: Materials, Integrations, and Applications

AbstractUltraviolet photodetectors (UV PDs) with “5S” (high sensitivity, high signal‐to‐noise ratio, excellent spectrum selectivity, fast speed, and great stability) have been proposed as promising optoelectronics in recent years. To realize high‐performance UV PDs, heterojunctions are created to form a built‐in electrical field for suppressing recombination of photogenerated carriers and promoting collection efficiency. In this progress report, the fundamental components of heterojunctions including UV response semiconductors and other materials functionalized with unique effects are discussed. Then, strategies of building PDs with lattice‐matched heterojunctions, van der Waals heterostructures, and other heterojunctions are summarized. Finally, several applications based on heterojunction/heterostructure UV PDs are discussed, compromising flexible photodetectors, logic gates, and image sensors. This work draws an outline of diverse materials as well as basic assembly methods applied in heterojunction/heterostructure UV PDs, which will help to bring about new possibilities and call for more efforts to unleash the potential of heterojunctions.

Fabrication of NiO/AlGaN heterojunction UV photodetector by low temperature aqueous method

A NiO/Al0.1Ga0.9N heterojunction structure was prepared using aqueous method. It was composed of NiO nanosheets and Al0.1Ga0.9N film. The device based NiO/Al0.1Ga0.9N heterojunction structure was sensitive to ultraviolet (UV) light illumination. It showed fast decay time of 34 ms and rise time of 30 ms. Moreover, high responsibility of 0.65 A W−1 was achieved at 365 nm UV illumination. The results showed high performance NiO/AlGaNheterojunction UV-photodetector can be obtained using simple way. Meanwhile, it may be promising candidates for novel nanostructures design and high performance device fabrication.

Enhancement in Performance of Transparent p‐NiO/n‐ZnO Heterojunction Ultrafast Self‐Powered Photodetector via Pyro‐Phototronic Effect

AbstractA high‐performance transparent p‐NiO/n‐ZnO heterojunction ultraviolet photodetector with a photovoltaic mode that exploits the pyro‐phototronic effect is demonstrated. The influence of thermal treatment on ZnO films is systematically investigated, and is found to help speed up current flow due to redistribution of the pyroelectric potential within the heterojunction device. The pyrocurrent magnitude is enhanced by 1264.41% for the thermally treated device. In addition, under weak UV illumination (0.43 mW cm−2), the thermally treated device exhibits high responsivity and detectivity with respective enhancements over 5460% and 6063% compared to the pristine device. Importantly, an ultrafast response speed with rise time ≈3.92 and decay time ≈8.90 µs is achieved under self‐biased conditions. The device also maintains an impressive transparency of more than 70% in the visible region. Furthermore, the basic pyro‐phototronic properties of the device are thoroughly probed based on the influence of incident light intensity, externally applied bias, and change in transient switching frequencies. This work not only introduces a simple approach but also enables high‐performance self‐powered UV photodetection governed by the pyro‐phototronic effect and demonstrated to be suitable for future transparent optoelectronic devices.

Enhanced photoresponse of n-ZnO/p-GaN heterojunction ultraviolet photodetector with high-quality CsPbBr3 films grown by pulse laser deposition

High-quality CsPbBr3 thin films have been fabricated by pulse laser deposition (PLD) technique and severed as an interlayer for n-ZnO/p-GaN heterojunction ultraviolet (UV) photodetector. The self-powered photodetectors based on n-ZnO/CsPbBr3/p-GaN heterojunction exhibited a high peak responsivity of 44.53 mA/W and detectivity of 2.03✕1012 cm·Hz1/2W−1 under zero bias voltage, which has increased ∼30 and ∼178 times than that of the n-ZnO/p-GaN device, respectively. Meanwhile, the photodetector with excellent stable and reproducible characteristics were also demonstrated and the photoresponse time has been drastically shortened by inserting the CsPbBr3 interlayer. The key role of the CsPbBr3 interlayer, as a carrier transport layer, has been demonstrated by the energy-band diagram. The enhanced performances of n-ZnO/p-GaN heterojunction make them promising application in self-powered photodetectors.

Wafer-scale synthesis of a uniform film of few-layer MoS2 on GaN for 2D heterojunction ultraviolet photodetector

Layered transition metal dichalcogenide materials grown over a conventional 3D semiconductor substrate have ignited a spark of interest in the electronics industry. The integration of these 2D layered materials extensively addresses the formidable challenges faced by a new generation of opto-electronic and photovoltaic devices. Herein, we have demonstrated a 2D/3D heterojunction type photodetector by depositing MoS2 on a GaN substrate with a mass-scalable sputtering method. Spectroscopic and microscopic characterizations expose the signature of the highly crystalline, homogeneous and controlled growth of a deposited few-layer MoS2 film. The greater light absorption of few-layer MoS2 results in the high performance of the MoS2/GaN photodetector. Our device shows high external spectral responsivity (~103 A W−1) and detectivity (~1011 Jones) with a very fast response time (~5 ms). Our obtained results are significantly better than previous MoS2- and GaN-based photodetectors. This work unveils a new perspective in MoS2/GaN heterojunctions for high-performance optoelectronic applications.

Trap assisted charge multiplication enhanced photoresponse of Li–P codoped p-ZnO/n-Si heterojunction ultraviolet photodetectors

In this work, we report a high-performance p-ZnO/n-Si heterojunction-based ultraviolet (UV) photodetector fabricated by dual ion beam sputter deposition. The lithium–phosphorus (Li–P) codoping route was used to realize low resistive and stable p-type ZnO. The current–voltage characteristics of p-ZnO/n-Si heterojunction photodiode showed good rectifying behavior with a rectification ratio of 170 at ±3 V. The spectral response measurements of the photodiode showed excellent responsivity with a peak observed around ~325 nm and cutoff wavelength around 370 nm. The maximum responsivity achieved was 2.6 A W−1 at an applied reverse bias of −6 V. The external quantum efficiency determined was of the order of ~1000% which is attributed to the trap assisted multiplication of charge carriers.

The effect of self-depleting in UV photodetector based on simultaneously fabricated TiO2/NiO pn heterojunction and Ni/Au composite electrode

A novel dark self-depleting ultraviolet (UV) photodetector based on a TiO2/NiO pn heterojunction was demonstrated and exhibited lower dark current (Idark) and noise. Both the NiO layer and Ni/Au composite electrode were fabricated by a smart, one-step oxidation method which was first employed in the fabrication of the UV photodetector. In dark, the depleted pn heterojunction structure effectively reduced the majority carrier density in TiO2/NiO films, demonstrating a high resistance state and contributing to a lower Idark of 0.033 nA, two orders of magnitude lower than that of the single-material devices. Under UV illumination, the interface self-depleting effect arising from the dissociation and accumulation of photogenerated carriers was eliminated, ensuring loss-free responsivity (R) and a remarkable specific detectivity (D*) of 1.56 × 1014 cm Hz1/2 W−1 for the optimal device. The device with the structure of ITO/TiO2/NiO/Au was measured to prove the mechanisms of interface self-depleting in dark and elimination of the depletion layer under UV illumination. Meanwhile, shortened decay time was achieved in the pn heterojunction UV photodetector. This suggests that the self-depleting devices possess the potential to further enhance photodetection performance.

Sb-Doped $p$ -MgZnO/ $n$ -Si Heterojunction UV Photodetector Fabricated by Dual Ion Beam Sputtering

Sb-doped p-Mg 0.1 Zn 0.9 O/n-Si-based heterojunction ultraviolet photodetectors were fabricated using dual ion beam sputtering. Current-Voltage measurements showed good rectifying behavior in fabricated devices with rectifying ratio as high as 251.35 at ± 4 V. The detectors exhibited good ultraviolet spectral response having peak responsivity of 0.025 A/W (at 310 nm) and 0.32 A/W (at 320 nm) at -30 V. The values of peak responsivity and external quantum efficiency increased from 1.7 mA/W and 0.75% (at 0 V) to 0.32 A/W and 134.26% (at -30 V), respectively. The value of detectivity of heterojunction devices was calculated to be 3.65 × 10 11 cm · Hz 1/2 ·W -1 at -5 V.

Physical properties of Al-doped MgZnO/AlGaN p–n heterojunction photodetectors

We report a p–n heterojunction ultraviolet photodetector (PD) based on an Al-doped MgxZn1−xO (AMZO)/Al0.08Ga0.92N heterojunction. AMZO films with 5 wt% of Al2O3 were deposited onto p–Al0.08Ga0.92N by using radio-frequency magnetron sputtering, and they were annealed at 700, 800, and 900 °C in a nitrogen ambient for 60 s. The photoluminescence spectra of the AMZO films were measured at 17 K and show two major peaks. A broad visible band could be attributed to the presence of structural defects. The AMZO film annealed at 800 °C showed a lower emission band in the visible region because of the presence of fewer defects compared with the other AMZO films. The wavelength that corresponds with the peak responsivity of the PD annealed at 800 °C was approximately 200 nm, and the cutoff wavelength was approximately 250 nm. Furthermore, the current–voltage characteristics of the Al0.08Ga0.92N/AMZO p–n junction PD showed a high leakage current. The PD annealed at 800 °C exhibited a dark current of 1.56 μA at a bias of −3 V.

Improved Photoresponse Performance of Self-Powered ZnO/Spiro-MeOTAD Heterojunction Ultraviolet Photodetector by Piezo-Phototronic Effect.

Strain-induced piezoelectric potential (piezopotential) within wurtzite-structured ZnO can engineer the energy-band structure at a contact or a junction and, thus, enhance the performance of corresponding optoelectronic devices by effectively tuning the charge carriers' separation and transport. Here, we report the fabrication of a flexible self-powered ZnO/Spiro-MeOTAD hybrid heterojunction ultraviolet photodetector (UV PD). The obtained device has a fast and stable response to the UV light illumination at zero bias. Together with responsivity and detectivity, the photocurrent can be increased about 1-fold upon applying a 0.753% tensile strain. The enhanced performance can be attributed to more efficient separation and transport of photogenerated electron-hole pairs, which is favored by the positive piezopotential modulated energy-band structure at the ZnO-Spiro-MeOTAD interface. This study demonstrates a promising approach to optimize the performance of a photodetector made of piezoelectric semiconductor materials through straining.

Fabrication and Characterization of TiO<sub>2</sub> Nanorod Array Based Visible-Blind Ultraviolet Photodetector by Hydrothermal Process

In this study, a TiO2 nanorod array based TiO2/water solid-liquid heterojunction ultraviolet photodetector, fabricated via a low-cost hydrothermal process is reported. The device exhibits several excellent characteristics such as self-powered, visible-blind and fast response, high photosensitivity, and linear variations in photocurrent for incident UV-light intensities. In addition, suggestions are provided to further improve device performance and increase the growth density of TiO2 nanorod array in the initial growth stage of the hydrothermal process to avoid the FTO surface being directly exposed to the electrolyte (water) which is a key factor in the developing direction.

Self-powered p-NiO/n-ZnO heterojunction ultraviolet photodetectors fabricated on plastic substrates

A self-powered ultraviolet (UV) photodetector (PD) based on p-NiO and n-ZnO was fabricated using low-temperature sputtering technique on indium doped tin oxide (ITO) coated plastic polyethylene terephthalate (PET) substrates. The p-n heterojunction showed very fast temporal photoresponse with excellent quantum efficiency of over 63% under UV illumination at an applied reverse bias of 1.2 V. The engineered ultrathin Ti/Au top metal contacts and UV transparent PET/ITO substrates allowed the PDs to be illuminated through either front or back side. Morphology, structural, chemical and optical properties of sputtered NiO and ZnO films were also investigated.