eh-Chung Yu

Solar-Blind Photodetectors for Harsh Electronics

We demonstrate solar-blind photodetectors (PDs) by employing AlN thin films on Si(100) substrates with excellent temperature tolerance and radiation hardness. Even at a bias higher than 200u2005V the AlN PDs on Si show a dark current as low as ~ 1u2005nA. The working temperature is up to 300°C and the radiation tolerance is up to 1013u2005cm−2 of 2-MeV proton fluences for AlN metal-semiconductor-metal (MSM) PDs. Moreover, the AlN PDs show a photoresponse time as fast as ~ 110u2005ms (the rise time) and ~ 80u2005ms (the fall time) at 5u2005V bias. The results demonstrate that AlN MSM PDs hold high potential in next-generation deep ultraviolet PDs for use in harsh environments.

Creation of high density ensembles of nitrogen-vacancy centers in nitrogen-rich type Ib nanodiamonds

This work explores the possibility of increasing the density of negatively charged nitrogen-vacancy centers ([NV(-)]) in nanodiamonds using nitrogen-rich type Ib diamond powders as the starting material. The nanodiamonds (10-100 nm in diameter) were prepared by ball milling of microdiamonds, in which the density of neutral and atomically dispersed nitrogen atoms ([N(0)]) was measured by diffuse reflectance infrared Fourier transform spectroscopy. A systematic measurement of the fluorescence intensities and lifetimes of the crushed monocrystalline diamonds as a function of [N(0)] indicated that [NV(-)] increases nearly linearly with [N(0)] at 100-200xa0ppm. The trend, however, failed to continue for nanodiamonds with higher [N(0)] (up to 390xa0ppm) but poorer crystallinity. We attribute the result to a combined effect of fluorescence quenching as well as the lower conversion efficiency of vacancies to NV(-) due to the presence of more impurities and defects in these as-grown diamond crystallites. The principles and practice of fabricating brighter and smaller fluorescent nanodiamonds are discussed.

Trilayered MoS

Trilayered MoS2 metal-semiconductor-metal (MSM) photodetectors (PDs) exhibit the photogain is up to 24 with high responsivity (~1.04 A/W). This is because photocarriers generated at the MoS2 between two Au electrodes drift toward the metal-semiconductor interfaces due to band bending under applied bias and are then trapped at the surface state sites at the Au/MoS2 interfaces, giving rise to the decrease in Schottky barrier height. Moreover, MoS2 MSM PDs show fast operation speed; as the contact spacing reduces from 8 to 4 μm, the rise time and fall time of PDs reduce from 70 to 40 μs and from 110 to 50 μs, respectively. Trilayered MoS2 MSM PDs can operate even after 2-MeV proton illumination with ~1011 cm-2 fluences, indicating the high radiation tolerance. This work demonstrates that trilayer MoS2 opens up a new dimension for 2-D nanomaterial applications in harsh electronics.

_{\bf 2}

A fully transparent resistive memory (TRRAM) based on Hafnium oxide (HfO2) with excellent transparency, resistive switching capability, and environmental stability is demonstrated. The retention time measured at 85u2009°C is over 3u2009×u2009104u2009sec, and no significant degradation is observed in 130 cycling test. Compared with ZnO TRRAM, HfO2 TRRAM shows reliable performance under harsh conditions, such as high oxygen partial pressure, high moisture (relative humidityu2009=u200990% at 85u2009°C), corrosive agent exposure, and proton irradiation. Moreover, HfO2 TRRAM fabricated in cross-bar array structures manifests the feasibility of future high density memory applications. These findings not only pave the way for future TRRAM design, but also demonstrate the promising applicability of HfO2 TRRAM for harsh environments.

Metal –Semiconductor–Metal Photodetectors: Photogain and Radiation Resistance

In this study, x-ray diffraction, scanning electron microscopy, micro-Raman spectroscopy, x-ray absorption near-edge structure and particle-induced x-ray emission are used to characterize the microstructure of (Zn, Cr)O films prepared using a co-sputtering method. We found that the Cr ions did not substitute for the Zn sites but instead formed Cr nano-particles and secondary oxide phases (SOPs) of Cr2O3 and/or ZnCr2O4 in co-sputtered Zn1−xCrxO films with Cr content x ≥ 0.1. Evidence is presented for the evolution of SOPs formed in (Zn, Cr)O films with increasing Cr sputtering power. Based on the inspection of the Cr and Zn contents in (Zn, Cr)O films, we conclude that the formation of the Cr2O3 phase is driven by a substantial increase in the atomic ratio of Cr/Zn, followed by the formation of a ZnCr2O4 phase promoted by a higher content of Cr than of Zn in film with increasing Cr sputtering power. It seems that a strong preference of Cr for octahedral rather than tetrahedral coordination with oxygen would trigger the formation of SOPs rather than the substitution of Cr into Zn sites and could be an obstacle for achieving a real Cr-substituted ZnO dilute magnetic oxide.

A Fully Transparent Resistive Memory for Harsh Environments.

This paper describes a fabrication and characterization of ultraviolet (UV) photodetectors based on Ohmic contacts using Pt electrode onto the epitaxial ZnO (0002) thin film. Plasma enhanced chemical vapor deposition (PECVD) system was employed to deposit ZnO (0002) thin films onto silicon substrates, and radio-frequency (RF) magnetron sputtering was used to deposit Pt top electrode onto the ZnO thin films. The as-deposited Pt/ZnO nanobilayer samples were then annealed at in two different ambients (argon and nitrogen) to obtain optimal Ohmic contacts. The crystal structure, surface morphology, optical properties, and wettability of ZnO thin films were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), photoluminescence (PL), UV-Vis-NIR spectrophotometer, and contact angle meter, respectively. Moreover, the photoconductivity of the Pt/ZnO nanobilayers was also investigated for UV photodetector application. The above results showed that the optimum ZnO sample was synthesized with gas flow rate ratio of 1 : 3 diethylzinc [DEZn, Zn(C2H5)2] to carbon dioxide (CO2) and then combined with Pt electrode annealed at in argon ambient, exhibiting good crystallinity as well as UV photo responsibility.

Structural and morphological evolution in magnetron co-sputtered (Zn, Cr)O films

The purpose of this study is to investigate how ion implantation affects the surface characteristics and nitrogenizing depth of the thin film by the use of a NEC 9SDH-2 3MV Pelletron accelerator that implants nitrogen ions into SKD-61 tool steels for surface modification. Nitrogen ions were implanted into the surface layer of materials so that the hardness of modified films could be improved. Also, the nitride film stripping problems of the traditional nitrogenizing treatment could be overcome by a new approach in surface process engineering. As nitrogen ions with high velocity impacted on the surface of the substrate, the ions were absorbed and accumulated on the surface of the substrate. The experiments were performed with two energies (i.e., 1 and 2MeV) and different doses (i.e., 2.5×1015, 7.5×1015, and 1.5×1016ions∕cm2). Nitrogen ions were incorporated into the interface and then diffused through the metal to form a nitride layer. Analysis tools included the calculation of stopping and range of ions i...

Postannealing Effect at Various Gas Ambients on Ohmic Contacts of Pt/ZnO Nanobilayers toward Ultraviolet Photodetectors

In this paper, we take advantage of a facile fabrication technique called self-assembled nanosphere lithography (SANSL) combining with proper two-step reactive ion etching (RIE) method and radio frequency (RF) sputtering deposition process for manufacturing honeycomb diamond-like carbon (DLC) thin film structures with hydrophobic and high transparent properties. It is found that the DLC thin films deposited on clean glass substrates at the RF power of 100 W with the surface roughness (Ra) of 2.08 nm and the ID/IG ratio of 1.96 are realized. With a fill-factor of 0.691, the honeycomb DLC patterned thin film shows the best transmittance performance of 87% in the wavelength of visible light, and the optimized contact angle measurement is ~108°. Compared with the pure DLC thin film and original glass substrate, the hydrophobic property of the patterned DLC films is significantly improved by 80 and 160%, respectively.

Surface modification of SKD-61 steel by ion implantation technique

In this paper, the metal-semiconductor-metal (MSM) Schottky AlN photodetectors (PDs) on Si substrates show a dark current as low as ~1 nA at a bias up to 200 V. Excellent thermal stability and radiation hardness of solar-blind AlN MSM PDs are achieved. The working temperature is up to 300 °C and the radiation tolerance is up to 1013 cm-2 of 2 MeV proton fluences for AlN MSM PDs. The results demonstrate the high promise of AlN as an active material for solar-blind DUV photodetection in extremely harsh environments.

Hydrophobic and high transparent honeycomb diamond-like carbon thin film fabricated by facile self-assembled nanosphere lithography

The effects of uniform structure defects produced by irradiation with 1.7 and 3 MeV protons on the electrical conductivity and low-field magnetoresistance (LFMR) of La0.67Sr0.33MnO3 (00l) films were investigated. The irradiation of heavy ions, such as Ar+ ions, usually creates defects, resulting in a decrease in the conductivity by defect scattering and an increase in the magnetoresistance by spin distortion. In the present study, the irradiation of light ions, such as protons, created low density point defects, resulting in structural and spin disorders, and an increase in the magnetoresistance. In contrast to the heavy-ion irradiation experiment, the conductivity markedly increased by more than two orders of magnitude.