Deep Ultraviolet Photodetectors Research Articles

Ga-In Nanoparticle Induced UV Plasmonic Impact on Heterojunction Based Deep UV Photodetector

Recent developments in Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -based heterostructures have opened a new area of applications for optoelectronic devices to be used extensively in deep-ultraviolet (UV) photodetection. Although heterostructure has an advantage in the suppression of high dark current, it also reduces the responsivity and photocurrent. In this context, Gallium-Indium (Ga-In) nanoparticles (NPs) have shown local surface plasmon resonance (LSPR) in the UV region and incorporated into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">/p</i> -CuO quasi-heterostructure based deep UV photodetectors (DUPDs) for performance enhancement. An inexpensive jejune electrospinning technique has been used to fabricate the photodetector on a sapphire (0001) substrate. After CuO and Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer deposition, sputtering has been used to deposit platinum (Pt) electrodes (50 nm) using a shadow mask. The Ga-In NPs have been drop-casted on top of the fabricated device. The device unveils a dark current of ∼1.03×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> A at 5 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> . Ga-In NPs induce LSPR that inflicts into a huge electron cloud. Extra electrons generated by LSPR reach the electrodes via the Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer and contribute to a very high photocurrent (∼1.14×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> ). Thus, present article illustrates an ultra-low dark current of Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -based DUPDs with upgraded photo responses by designing a p/n heterojunction with plasmonic NPs.

Photoinduced carrier transport mechanism in pn- and nn-GaN/GaON heterojunctions

The unexpected high persistent photoconductivity effect in Ga2O3 material hinders the application of deep-ultraviolet photodetectors, while GaON can effectively avoid the effect caused by oxygen vacancies through anion engineering. As the behaviors of the carrier’s transport are crucial and essential to the photoelectric conversion processes, analysis of the carrier transport mechanism is helpful to propose feasible and effective strategies for high-performance photodetectors. In this work, GaN/GaON pn- and nn-heterojunctions with various thicknesses of GaON thin films were obtained by oxidizing the n-GaN and p-GaN films, and their photoinduced carrier transport mechanism has been comprehensively investigated. At a low bias, as the electric field is limited in the GaON layer and only the carriers generated in the GaON layer can be collected by the electrodes for both GaN/GaON pn- and nn-heterojunctions, the current increases linearly with an increase in the voltage. At a high bias, the electric field can affect the GaN/GaON heterojunction interface. For the GaN/GaON nn-heterojunction, the current continues to increase with increasing voltage as a small potential barrier is created between GaON and n-GaN to separate and transport the photogenerated carriers. However, for the GaN/GaON pn-heterojunction, the current increases slowly and then rapidly with an increase in the high voltage, because the electric field is not strong enough to help the carriers cross the potential barrier caused by the reverse GaN/GaON pn-heterojunction first and then overcome the barrier with a higher voltage.

Construction of α-Ga2O3-ZnO heterojunction for a promoted performance applied in self-powered solar blind photodetector

Gallium oxide-based photoelectrochemical photodetectors (PEC-PDs) have received extensive attention for their natural self-powered characteristic and detection capability in solar-blind region. In this work, ZnO nanoparticles decorated α-Ga2O3 nanorods heterojunction (α-Ga2O3-ZnO) are synthesized on FTO conductive glass substrates as photoanodes for PEC-PDs. The efficient regulation of performance for α-Ga2O3-ZnO heterojunction PEC-PDs is achieved by varying the ZnO nanoparticles concentration. Experimental results show that all devices exhibit self-powered solar blind detection characteristics and the performance of ZnO nanoparticles decorated devices are all better than that of pristine α-Ga2O3. When the concentration of ZnO nanoparticles reaches to a certain value, the responsivity attains the maximum value as high as 34.2 mA/W, and the response time is as low as 0.25/0.18 s. Combined with first-principles calculations, the mechanism of the improved performance is discussed in detail. The results reveal that that the contact between α-Ga2O3 and ZnO can induce charges transfer, which constitutes a built-in electric field that acts as a driving force to separate the photogenerated carriers into different sections. This process can effectively prevent the recombination of photogenerated carriers and prolong the lifetime of e––h+, thus improve the overall detection performance finally. This work will provide meaningful guidance for the development of novel high-performance self-powered solar-blind deep-UV photodetectors.

Bidirectional Control of the Band Bending at the (2̅01) and (010) Surfaces of β-Ga2O3 Using Aryldiazonium Ion and Phosphonic Acid Grafting

Beta gallium oxide (β-Ga2O3) is an ultrawide-bandgap semiconductor with one of the highest-known breakdown strengths (∼8 MV/cm) making it a strong candidate for high-efficiency power electronics, deep-ultraviolet photodetectors, and transparent electronic devices. Bare β-Ga2O3 surfaces exhibit a strong upward band bending and electron depletion that is reduced by the formation of a hydroxyl termination on exposure to the atmosphere, although this effect varies with exposure conditions and the processing history of different samples. This work investigates the covalent modification of (2̅01) and (010) β-Ga2O3 surfaces with organic layers, as a mechanism for more effectively controlling their surface band bending. We compare the different electronic effects of grafted layers formed by the electrochemical reduction of 4-nitrobenzenediazonium ions and the spontaneous grafting of octadecylphosphonic acid (ODPA). Atomic force microscopy, synchrotron X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure spectroscopy confirmed the presence of few-nanometer layers of covalently attached nitrophenyl (NP) and ODPA molecules. Valence band XPS showed that NP modification produced upward band bending shifts of +0.51 and +0.53 eV on (2̅01) and (010) β-Ga2O3, respectively, with further increases of +0.35 and +0.20 eV after X-ray-induced reduction of the nitro substituent to amino-like moieties. In contrast, ODPA modification produced downward shifts in surface band bending of −0.36 and −0.07 eV on (2̅01) and (010) β-Ga2O3, respectively. Our study demonstrates that covalently bound NP and ODPA molecules can be used to significantly modify the electronic properties of β-Ga2O3 surfaces, a finding that should prove useful for electronic applications of this material.

Ultrafast Deep-Ultraviolet Laser-Induced Voltage Response of Pyrite.

Ultrafast, high-sensitivity deep-ultraviolet (UV) photodetectors are crucial for practical applications, including optical communication, ozone layer monitoring, flame detection, etc. However, fast-response UV photodetectors based on traditional materials suffer from issues of expensive production processes. Here, we focused on pyrite with simultaneously cheap production processes and ultrafast response speed. Nanoseconds photovoltaic response was observed under UV pulsed laser irradiation without an applied bias at room temperature. In addition, the response time of the laser-induced voltage (LIV) signals was ~20 ns, which was the same as the UV laser pulse width. The maximum value of the responsivity is 0.52 V/mJ and the minimum value of detectivity was about to ~1.4 × 1013 Jones. When there exists nonuniform illumination, a process of diffusion occurs by which the carriers migrate from the region of high concentration toward the region of low concentration. The response speed is limited by a factor of the diffusion of the carriers. With an increment in laser energy, the response speed of LIV is greatly improved. The high response speed combined with low-cost fabrication makes these UV photodetectors highly attractive for applications in ultrafast detection.

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 Hz1/2 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.

Solar-blind ultraviolet photodetectors with thermally reduced graphene oxide formed on high-Al-content AlGaN layers

Solar-blind deep-ultraviolet (UV) photodetectors (PDs) with high responsivity and fast response have attracted significant attention in environmental, industrial, biological, and military applications. AlGaN is a representative semiconductor material in the field of solar-blind detection; semiconductor performance can be accelerated by combining it with high-transparency, high-stability contact electrode materials. In this study, solar-blind deep-UV metal–semiconductor–metal (MSM) PDs were fabricated based on two-dimensional reduced graphene oxide (rGO) contacts formed on various high-Al-content AlGaN semiconductors. A low dark current in the order of a few picoamperes and a fast photoresponse time of a few tens of milliseconds were confirmed. The investigation of the effects of front- and back-side illumination showed that the photocurrents and corresponding responsivities of the PDs drastically improved under back-side illumination. In detail, the peak locations of the responsivity–wavelength curves were downshifted from 290 nm with a responsivity of 0.0518 A/W for the rGO/Al0.5Ga0.5N MSM PD to 250 nm with a responsivity of 0.0113 A/W for the rGO/Al0.7Ga0.3N MSM PD under back-side illumination. These results indicate that rGO contacts on AlGaN provide a viable approach for developing solar-blind deep-UV PDs.

Solution Spin-Coated BiFeO3 Onto Ga2O3 Towards Self-Powered Deep UV Photo Detector of Ga2O3/BiFeO3 Heterojunction

Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is one of the most suitable semiconductor materials for performing deep UV photoelectric detection. In this work, a self-powered deep UV photodetector based on a Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /BFO heterojunction is fabricated via solution spin-coating and metal-organic chemical vapor deposition (MOCVD) methods. Without biasing driven, the device achieves an extreme low dark current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{dark}$ </tex-math></inline-formula> ) of 8.38 fA, a photo-to-dark current ratio ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PDCR</i> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.66\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , a high specific detectivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} \ast $ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.1\times 10^{12}$ </tex-math></inline-formula> Jones and an open-circuit voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\textit {oc}}$ </tex-math></inline-formula> ) of 0.55 V responding to deep UV irradiation (254 nm in this work). Through analyzing the band diagram of the heterojunction, the intrinsic physical characteristics of the photodetector are discussed. Results show that the photodetector has excellent deep UV signal detecting ability, indicating that Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /BFO heterojunction is a potential candidate for performing self-powered deep UV photodetection.

Role of Interfacial Oxide in the Preferred Orientation of Ga2O3 on Si for Deep Ultraviolet Photodetectors.

It is generally known that a layer of amorphous silicon oxide (SiO2) naturally exists on the surface of silicon, resulting in the growth of gallium oxide (Ga2O3) that is no longer affected by substrate crystallinity during sputtering. This work highlights the formation energy between the native amorphous nano-oxide film formed on the Si substrate and monoclinic β-Ga2O3 dominating the preferred orientation prepared for deep ultraviolet photodetectors. The latter were deposited on p-type silicon (p-Si) with (111) orientation using radio frequency sputtering at 600 °C and post rapid thermal annealing (RTA). The X-ray diffraction (XRD) results indicate both as-deposited and postannealing films with the (400) preferred orientation for a layer thickness of 100 nm. However, slight random orientation with the amorphous structure is mixed in the preferred one for the as-deposited film with a thickness of 200 nm and reduced after being annealed at 800 °C, which is observed by XRD and transmission electron microscopy. Meanwhile, thermal-induced massive twin boundaries (TBs) and stacking faults (SFs) were generated when annealed at 1000 °C, owing to the relaxation of lattice strain by the coherent interface. The interfacial bonding energy per unit area (Ei) between β-Ga2O3 films with various facets ((001), (010), (100), and (2̅01)) and amorphous SiO2 was calculated using density functional theory. The Ei of β-Ga2O3 (100)/SiO2 reveals the highest value (0.289 eV/Å2), which is consistent with the (100) preferred orientation of deposited films. The (100) preferred orientation is the driving force for TBs and SFs. The discrimination of responsivities and the photo/dark current contrast ratio (Iph/Idark) are inversely proportional to the amorphous structure, grain boundaries, TBs, and SFs. Therefore, optimum metal–semiconductor–metal photodetector performance is achieved for RTA-treated samples at 800 °C with an Iph/Idark of 3.91 × 102 and a responsivity of 0.702 A/W (λpeak = 230 nm) at 5 V bias for a 200 nm thin film.

Performance Improvement of Amorphous Ga2O3/P-Si Deep Ultraviolet Photodetector by Oxygen Plasma Treatment

Gallium oxide (Ga2O3) is an attractive semiconductor that is very suitable for deep ultraviolet (DUV) inspection. However, due to the existence of many types of oxygen vacancies in the amorphous Ga2O3 (a-Ga2O3) film, it greatly limits the performance of the a-Ga2O3-based photodetector. Here, we perform oxygen plasma treatment on the a-Ga2O3/p-Si photodetector to reduce the concentration of oxygen vacancies in the a-Ga2O3 film, so that the dark current is reduced by an order of magnitude (from 1.01 × 10−3 A to 1.04 × 10−4 A), and the responsivity is increased from 3.7 mA/W to 9.97 mA/W. In addition, oxygen plasma processing makes the photodetector operate well at 0 V bias. The response speed is that the rise time is 2.45 ms and the decay time is 1.83 ms, while it does not respond to the DUV illumination without oxygen plasma treating at a zero bias. These results are attributed to the fact that oxygen plasma treatment can reduce the Schottky barrier between a-Ga2O3 and the electrode indium tin oxide (ITO), which promotes the separation and collection efficiency of photo-generated carriers. Therefore, this work proposes a low-cost method to improve the performance of Ga2O3 film-based DUV photodetectors.

Tuning the Plasmonic Resonance Peak for Al Nanorods on AlGaN Layer to Deep Ultraviolet Band

Tuning the plasmonic resonance peak to the deep ultraviolet (DUV) band is critical for plasmonic-enhanced AlGaN-based DUV photodetector. However,the high refractive index of AlGaN layer seriously limits the plasmonic resonance peak in DUV band. Therefore, in this work, we study how various Al nanoparticles on the AlGaN layer surface affect the plasmonic resonance performance. Compared with the Al-based nanosphere, nanohemisphere and nanodisk, the Al-based nanorod is the most suitable candidate for AlGaN-based DUV photodetectors. This is because the DUV plasmonic dipolar mode excited from the upper part of nanorod is not affected by the interface between the nanorods and the AlGaN layer. However, the interface also leads to another plasmonic dipolar mode at longer wavelengths. Moreover, the DUV plasmonic resonance peak will be influenced by the diameter, the height and the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer thickness. We also find that the diffraction can enhance the resonance peak intensity when the Al nanorod period is smaller than the resonance peak wavelength. Besides, to make the enhanced electric field located in active layer, a layer of Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> shell is proposed to cover Al nanorods, which causes a quadrupole mode in DUV band excited from the sidewall of Al nanorods.

High-sensitive, self-powered deep UV photodetector based on p-CuSCN/n-Ga2O3 thin film heterojunction

Herein, a CuSCN/Ga2O3 heterojunction device was fabricated by spin-coating and metal-organic chemical vapor deposition (MOCVD) methods. Under the irradiation of 254 nm deep ultraviolet (DUV) light with an intensity of 1000 μW/cm2, the device shown high sensitivity and favorable self-powered performances with photo-to-dark current ratio (PDCR) of 1.29 × 104, photo responsivity (R) of 5.5 mA/W, rejection ratio (R270nm/R600nm) of 4.33 × 103, and specific detectivity (D∗) of 3.8 × 1011 cm Hz1/2W−1 (Jones) at −5 V. In addition, the device has a rise time of 0.45 s and 3.80 s, and a decay time of 0.26 s and 0.26 s. In general, the CuSCN/Ga2O3 heterojunction prepared in this work may well be a potential candidate for achieving a self-powered and high-performance DUV photodetector.

Cerium‐Doped Perovskite Nanocrystals for Extremely High‐Performance Deep‐Ultraviolet Photoelectric Detection

AbstractIn this study, a novel deep‐ultraviolet photodetector (DUVPD) based on the hybrids of solution‐processed CsPbX3 (X = Cl, Br):Ce3+ perovskite nanocrystals (PNCs) and plasmonic Al film is presented. The optical absorption strength of the CsPbX3:Ce3+ PNCs is improved by one order of magnitude in the solar‐blind DUV range (200–280 nm) compared with the undoped. First‐principles calculations and Dorenbos's 4f and 5d host referred binding energy (HRBE) models prove that such an improvement results from the 4f–5d transition of Ce3+. The presence of Al film further improves the optical absorption strength in this DUV range due to the plasmonic effect and the metal−perovskite junction between Al film and perovskite. Finally, the DUVPDs based on CsPbCl3:Ce3+/Al hybrids demonstrate extremely high detectivity of 4 × 1013 Jones. This work is the first approach to build up high‐performance DUVPDs based on the doped PNCs.

Transport Mechanism of Enhanced Performance in an Amorphous/Monoclinic Mixed-Phase Ga2O3 Solar-Blind Deep Ultraviolet Photodetector

Recently, as an emerging material, ultrawide bandgap Ga2O3 has been investigated extensively in solar-blind deep-ultraviolet (DUV) photodetectors (PDs). High sensitivity and signal-to-noise ratio of PDs are essential for the detection of solar-blind DUV signals; however, such factors are often not mutually compatible. In the present study, an amorphous/monoclinic homogeneous mixed-phase structure was demonstrated to be significantly beneficial in enhancing the comprehensive performance of Ga2O3 solar-blind DUV PDs, especially with respect to sensitivity and the signal-to-noise ratio. Further experimental and theoretical findings provide insights on the transport mechanism of enhanced performance in the mixed-phase Ga2O3 solar-blind DUV PD. For effectively separating the photogenerated carriers, a type-II band alignment between amorphous and crystalline Ga2O3 can be exploited. Furthermore, the change of the barrier height of the mixed-phase interface also has a significant impact on the transport properties of the mixed-phase Ga2O3 PD. Additionally, the potential applications of mixed-phase Ga2O3 PD in high-voltage corona discharge were explored, and clear and stable corona discharge signals were obtained. The results of the present study may promote understanding of DUV photoelectronic devices with various mixed-phase Ga2O3 materials and provide an efficient approach for promoting comprehensive performance in future solar-blind detection applications.

Heteroepitaxial growth of β-Ga2O3 thin films on c-plane sapphire substrates with β-(AlxGa1-x)2O3 intermediate buffer layer by mist-CVD method

As a new-type of ultra-wide bandgap semiconductor, β-Ga2O3 has received widespread attention due to its great potential applications in high-power devices and deep ultraviolet photodetectors. However, the conventional material epitaxial growth methods (such as MBE, MOCVD and HVPE) are always based on the expensive vacuum equipment and time-consuming. In this work, a low-cost and non-vacuum mist-CVD method is used to grow β-Ga2O3 films heteroepitaxially on sapphire substrates. In order to improve the quality of β-Ga2O3 films, the β-(AlxGa1-x)2O3 is first grown on sapphire substrate and used as the intermediate buffer layer to epitaxially grow β-Ga2O3 film, which can decrease the lattice mismatch and improve the β-Ga2O3 quality. A series of characterization techniques are used to characterize the properties of samples. The results of XPS and UV-Vis tests show that the aluminum composition of β-(AlxGa1-x)2O3 films grown at 850 °C and 900 °C are 0.24 and 0.43, respectively, and the corresponding band gap is 5.36 eV and 5.55 eV respectively. After using β-(AlxGa1-x)2O3 as the intermediate buffer layer, the FWHM of β-Ga2O3 film is 1.131°, the RMS roughness is 3.04 nm, and it has an ideal band gap (4.91 eV), which demonstrates the obvious improvement compared to the sample without the intermediate buffer layer. This shows that β-(AlxGa1-x)2O3 as an intermediate buffer layer can significantly improve the quality of heteroepitaxially grown β-Ga2O3 films.

Fully transparent InZnSnO/β-Ga2O3/InSnO solar-blind photodetectors with high schottky barrier height and low-defect interfaces

Ultra-wide bandgap β-Ga2O3 photodiodes have received great attention due to transparent solar-blind deep ultraviolet photodetectors. We demonstrated an all oxide-based single-crystal β-Ga2O3 photodiode incorporated with transparent conductive InZnSnO and InSnO as Schottky and Ohmic contacts, respectively. High work function and low resistivity of InZnSnO allow for clear rectifying characteristics with a low dark current (<0.1 nA) of up to −100 V of reverse bias. The Schottky barrier height and junction defects at the Schottky interface were modified using post-annealing treatment, thereby influencing the deep ultraviolet photoresponse. The responsivity of the annealed device was 9.6 mA/W, decreasing the Schottky barrier height engineering, while the photo responding speed was degraded and caused a persistent photocurrent effect due to the generation of defect states.

Heteroepitaxial β‐Ga2O3 on Conductive Ceramic Templates: Toward Ultrahigh Gain Deep‐Ultraviolet Photodetection (Adv. Mater. Technol. 9/2021)

Deep-Ultraviolet Photodetector Nasir Alfaraj, Boon S. Ooi, and colleagues demonstrate a deep-ultraviolet photodetector with remarkable photosensitivity in article number 2100142. Their novel device topology is realized through the disordered nucleation of beta-polymorph Ga2O3 crystals on monocrystalline TiN interlayers forming an oxide–nitride vertical heterostructure stack housed on a MgO substrate. A spectral responsivity of 276 A/W at an illuminating power density of around 70 μW/cm2 is achieved.

Performance enhancement of ZnGa2O4 Schottky type deep-ultraviolet photodetectors by oxygen supercritical fluid treatment

For semiconductor device applications such as FinFET, MEMS, 2D materials, and wide bandgap materials, reliability is one of the most powerful key factors for commercialization in the industry. ZnGa2O4 deep ultraviolet (DUV) photodetectors (PDs) have been studied for their reliability and hence have been examined using the accelerated life test (ALT), which has shown the poor reliability of the device and device degradation such as high leakage current and poor rise time falling time (Tr/Tf) ratios. Therefore, in this paper, we proposed a method to enhance device performance by a non-destructive post-treatment method with low temperature and high-pressure oxygen supercritical fluid (SCF-O) for DUV photodetectors. This method not only improved the device performance but allowed it to perform even better than the as-grown sample. X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscope analyses corroborated better crystallinity with a smaller number of interstitial defects followed by mathematical modelling using density functional theory. The on/off ratio increased from 102 to 105 and had an improved rise time and fall time ratio (Tr/Tf). The responsivity for the SCF-O treated ZnGa2O4 PDs (@240 nm) increased to 639 A/W as compared with that (486 A/W) of as-grown sample. The first-principles DFT-GGA calculations were used to explain the relationship between the formation energies of defects in the oxygen treatment on the ZnGa2O4 epitaxial layers and agreed well with the experiment results. As per our knowledge, our study was the first to present this post-treatment method for DUV photodetectors, which could increase the lifetime of semiconductor devices.

Deep-Level Traps Responsible for Persistent Photocurrent in Pulsed-Laser-Deposited β-Ga2O3 Thin Films

Gallium oxide (β-Ga2O3) is emerging as a promising wide-bandgap semiconductor for optoelectronic and high-power electronic devices. In this study, deep-level defects were investigated in pulsed-laser-deposited epitaxial films of β-Ga2O3. A deep ultraviolet photodetector (DUV) fabricated on β-Ga2O3 film showed a slow decay time of 1.58 s after switching off 250 nm wavelength illumination. Generally, β-Ga2O3 possesses various intentional and unintentional trap levels. Herein, these traps were investigated using the fractional emptying thermally stimulated current (TSC) method in the temperature range of 85 to 473 K. Broad peaks in the net TSC curve were observed and further resolved to identify the characteristic peak temperature of individual traps using the fractional emptying method. Several deep-level traps having activation energies in the range of 0.16 to 1.03 eV were identified. Among them, the trap with activation energy of 1.03 eV was found to be the most dominant trap level and it was possibly responsible for the persistent photocurrent in PLD-grown β-Ga2O3 thin films. The findings of this current work could pave the way for fabrication of high-performance DUV photodetectors.

Band alignment analysis of CuGaO2/β-Ga2O3 heterojunction and application to deep-UV photodetector

Single-oriented CuGaO2 films have been successfully grown on β-Ga2O3 (2¯01) substrate by reactive deposition epitaxy. The energy band offsets and alignment at CuGaO2/β-Ga2O3 heterojunction are investigated by x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). A type-II band alignment is identified at CuGaO2/β-Ga2O3 heterojunction with valence band offset (VBO) of 1.63 eV and conduction band offset (CBO) of 0.45 eV. The CuGaO2/β-Ga2O3 heterojunction based ultraviolet photodetector is prepared which exhibits an obvious ultraviolet (UV) photoresponse at zero bias voltage. The combination between β-Ga2O3 and wide bandgap delafossite oxide semiconductor may open up possibilities for next generation self-power deep UV optoelectronic devices in future.