Sol-Gel Synthesized Amorphous (InxGa1-x)2O3 for UV Photodetection with High Responsivity

β-Ga2O3 photodetectors have the advantages of low dark current and strong radiation resistance in UV detection. However, the limited photocurrent has restricted their applications. Herein, MSM UV photodetectors based on (InxGa1-x)2O3 (x = 0, 0.1, 0.2, 0.3) by a sol-gel method were fabricated and studied. The doping of indium ions in Ga2O3 leads to lattice distortion and promotes the formation of oxygen vacancies. The oxygen vacancies in (InxGa1-x)2O3 can be modulated by various proportions of indium, and the increased oxygen vacancies contribute to the enhancement of electron concentration. The results show that the amorphous In0.4Ga1.6O3 photodetector exhibited improved performances, including a high light-to-dark current ratio (2.8 × 103) and high responsivity (739.2 A/W). This work provides a promising semiconductor material In0.4Ga1.6O3 for high-performance MSM UV photodetectors.

Hardware-Intrinsic Physical Unclonable Functions by Harnessing Nonlinear Conductance Variation in Oxide Semiconductor-Based Diode

With the advancement of the Internet of Things (IoT), numerous electronic devices are connected to each other and exchange a vast amount of data via the Internet. As the number of connected devices increases, security concerns have become more significant. As one of the potential solutions for security issues, hardware intrinsic physical unclonable functions (PUFs) are emerging semiconductor devices that exploit inherent randomness generated during the manufacturing process. The unclonable security key generated from PUF can address the inherent limitations of conventional electronic systems which depend solely on software. Although numerous PUFs based on the emerging memory devices requiring switching operations have been proposed, achieving hardware intrinsic PUF with low power consumption remains a key challenge. Here, we demonstrate that the process-induced nonlinear conductance variations of oxide semiconductor-based Schottky diodes provide a suitable source of entropy for the implementation of PUF without switching operation. Using a mild oxygen plasma treatment, the surface electron accumulation layer that forms naturally in oxide semiconductor film can be partially eliminated, resulting in a large variation of nonlinearity as an exotic entropy source. The mild plasma-treated Schottky diodes showed near ideal 50% average uniformity and uniqueness, as well as an ideal entropy value without the need for additional hardware area and power costs. These findings will pave the way for the development of hardware intrinsic PUFs to realize energy-efficient cryptographic hardware.

Effects of Seed-Layer N2O Plasma Treatment on ZnO Nanorod Based Ultraviolet Photodetectors: Experimental Investigation with Two Different Device Structures

The crystalline quality of ZnO NR (nanorod) as a sensing material for visible blind ultraviolet PDs (photodetectors) critically depends on the SL (seed layer) material of properties, which is a key to high-quality nanocrystallite growth, more so than the synthesis method. In this study, we fabricated two different device structures of a gateless AlGaN/GaN HEMT (high electron mobility transistor) and a photoconductive PD structure with an IDE (interdigitated electrode) pattern implemented on a PET (polyethylene terephthalate) flexible substrate, and investigated the impact on device performance through the SL N₂O plasma treatment. In case of HEMT-based PD, the highest current on-off ratio (~7) and spectral responsivity R (~1.5 × 10⁵ A/W) were obtained from the treatment for 6 min, whereas the IDE pattern-based PD showed the best performance (on-off ratio = ~44, R = ~69 A/W) from the treatment for 3 min and above, during which a significant etch damage on PET substrates was produced. This improvement in device performance was due to the enhancement in NR crystalline quality as revealed by our X-ray diffraction, photoluminescence, and microanalysis.

Atomic-Thin ZnO Sheet for Visible-Blind Ultraviolet Photodetection

The atomic-thin 2D semiconductors have emerged as plausible candidates for future optoelectronics with higher performance in terms of the scaling process. However, currently reported 2D photodetectors still have huge shortcomings in ultraviolet and especially visible-blind wavelengths. Here, a simple and nontoxic surfactant-assisted synthesis strategy is reported for the controllable growth of atomically thin (1.5 to 4 nm) ZnO nanosheets with size ranging from 3 to 30 µm. Benefit from the short carbon chains and the water-soluble ability of sodium dodecyl sulfate (SDS), the synthesized ZnO nanosheets possess high crystal quality and clean surface, leading to good compatibility with traditional micromanufacturing technology and high sensitivity to UV light. The photodetectors constructed with ZnO demonstrate the highest responsivity (up to 2.0 × 10⁴ A W^-1 ) and detectivity (D* = 6.83 × 10¹⁴ Jones) at a visible-blind wavelength of 254 nm, and the photoresponse speed is optimized by the 400 °C annealing treatment (τ_R  = 3.97 s, τ_D  = 5.32 s), thus the 2D ZnO can serve as a promising material to fill in the gap for deep-UV photodetection. The method developed here opens a new avenue to controllably synthesize 2D nonlayered materials and accelerates their applications in high-performance optoelectronic devices.

Enhancement in the photonic response of ZnO nanorod-gated AlGaN/GaN HEMTs with N2O plasma treatment

We demonstrate an improvement in the photoresponse characteristics of ultraviolet (UV) photodetectors (PDs) using the N₂O plasma-treated ZnO nanorod (NR) gated AlGaN/GaN high electron mobility transistor (HEMT) structure. The PDs fabricated with ZnO NRs plasma-treated for 6 min show superior performance in terms of responsivity (∼1.54×10 ⁵ A/W), specific detectivity (∼ 4.7×10¹³ cm·Hz^-1/2/W), and on/off current ratio (∼40). These improved performance parameters are the best among those from HEMT-based PDs reported to date. Photoluminescence analysis shows a significant enhancement in near band edge emission due to the effective suppression of native defects near the surface of ZnO NRs after plasma treatment. As our X-ray photoelectron spectroscopy reveals a very high O/Zn ratio of ∼0.96 from the NR samples plasma-treated for 6 min, the N₂O plasma radicals also show a clear impact on ZnO stoichiometry. From our X-ray diffraction analysis, the plasma-treated ZnO NRs show much greater improvement in (002) peak intensity and degree of (002) orientation (∼0.996) than those of as-grown NRs. This significant enhancement in (002) degree of orientation and stoichiometry in ZnO nano-crystals contribute to the enhancement in photoresponse characteristics of the PDs.

The Influence of Different Partial Pressure on the Fabrication of InGaO Ultraviolet Photodetectors

A metal–semiconductor–metal ultraviolet photodetector has been fabricated with a radiofrequency (RF)-sputtered InGaO thin film. Results for the devices fabricated under different oxygen partial pressure are here in discussed. Under low oxygen partial pressure, the devices work in the photoconductive mode because of the large number of subgap states. Therefore, the devices exhibit internal gain. These defects in the films result in slow switching times and lower photo/dark current ratios. A higher flow ratio of oxygen during the sputtering process can effectively restrain the oxygen vacancies in the film. The responsivity of the photodetector fabricated under an oxygen flow ratio of 20% can reach 0.31 A/W. The rise time and decay time can reach 21 s and 27 s, respectively.

Ultrathin Co-O oxide layer-driven perpendicular magnetic anisotropy in a CoO/[Co/Pd]m multilayer matrix upon annealing

Ferromagnetic/noble metal multilayer (ML) frames are expected to serve as reliable building blocks in a variety of perpendicular magnetic anisotropy (PMA) based spintronic devices. However, ultrathin ML matrices are highly susceptible to unintended reduction of electron spin polarization in the as-grown or annealed states and often require a large repeat number. Here, we introduce a simple approach to achieve thermally stable PMA in ultrathin [Co/Pd]₃ MLs involving the incorporation of an ultrathin CoO capping layer. The thickness and oxygen content of the CoO layer are critical parameters to achieve enhanced PMA in ultrathin [Co/Pd]₃/CoO MLs post-annealed up to 400 °C. An extensive analysis of structural features identified that robust PMA characteristics in [Co/Pd]₃/CoO MLs are linked with thermally activated oxygen atom diffusion leading to structural reconfiguration upon annealing. The possible origin of the enhanced PMA in our [Co/Pd]₃/CoO ML samples after high-temperature annealing is discussed, thereby enabling their use in future spintronic-related devices.

A Study on the Electrical Properties of Atomic Layer Deposition Grown InOx on Flexible Substrates with Respect to N2O Plasma Treatment and the Associated Thin-Film Transistor Behavior under Repetitive Mechanical Stress

Indium oxide (InO_x) films were deposited at low processing temperature (150 °C) by atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1) as the metal precursor and hydrogen peroxide (H₂O₂) as the oxidant. As-deposited InO_x exhibits a metallic conductor-like behavior owing to a relatively high free-carrier concentration. In order to control the electron density in InO_x layers, N₂O plasma treatment was carried out on the film surface. The exposure time to N₂O plasma was varied (600-2400 s) to evaluate its effect on the electrical properties of InO_x. In this regard, thin-film transistors (TFTs) utilizing this material as the active layer were fabricated on polyimide substrates, and transfer curves were measured. As the plasma treatment time increases, the TFTs exhibit a transition from metal-like conductor to a high-performance switching device. This clearly demonstrates that the N₂O plasma has an effect of diminishing the carrier concentration in InO_x. The combination of low-temperature ALD and N₂O plasma process offers the possibility to achieve high-performance devices on polymer substrates. The electrical properties of InO_x TFTs were further examined with respect to various radii of curvature and repetitive bending of the substrate. Not only does prolonged cyclic mechanical stress affect the device properties, but the bending direction is also found to be influential. Understanding such behavior of flexible InO_x TFTs is anticipated to provide effective ways to design and achieve reliable electronic applications with various form factors.

Structure deformation of indium oxide from nanoparticles into nanostructured polycrystalline films by in situ thermal radiation treatment

A microstructure deformation of indium oxide (In2O3) nanoparticles by an in situ thermal radiation treatment in nitrous oxide plasma was investigated. The In2O3 nanoparticles were completely transformed into nanostructured In2O3 films upon 10 min of treatment time. The treated In2O3 nanoparticle sample showed improvement in crystallinity while maintaining a large surface area of nanostructure morphology. The direct transition optical absorption at higher photon energy and the electrical conductivity of the In2O3 nanoparticles were significantly enhanced by the treatment.

Interface studies of N2 plasma-treated ZnSnO nanowire transistors using low-frequency noise measurements

Due to the large surface-to-volume ratio of nanowires, the quality of nanowire-insulator interfaces as well as the nanowire surface characteristics significantly influence the electrical characteristics of nanowire transistors (NWTs). To improve the electrical characteristics by doping or post-processing, it is important to evaluate the interface characteristics and stability of NWTs. In this study, we have synthesized ZnSnO (ZTO) nanowires using the chemical vapor deposition method, characterized the composition of ZTO nanowires using x-ray photoelectron spectroscopy, and fabricated ZTO NWTs. We have characterized the current-voltage characteristics and low-frequency noise of ZTO NWTs in order to investigate the effects of interface states on subthreshold slope (SS) and the noise before and after N2 plasma treatments. The as-fabricated device exhibited a SS of 0.29 V/dec and Hooge parameter of ~1.20 × 10(-2). Upon N2 plasma treatment with N2 gas flow rate of 40 sccm (20 sccm), the SS improved to 0.12 V/dec (0.21 V/dec) and the Hooge parameter decreased to ~4.99 × 10(-3) (8.14 × 10(-3)). The interface trap densities inferred from both SS and low-frequency noise decrease upon plasma treatment, with the highest flow rate yielding the smallest trap density. These results demonstrate that the N2 plasma treatment decreases the interface trap states and defects on ZTO nanowires, thereby enabling the fabrication of high-quality nanowire interfaces.