Ultrahigh-temperature microwave annealing of Al⁺- and P⁺-implanted 4H-SiC

In this work, an ultrafast solid-state microwaveannealing has been performed, in the temperature range of 1700–2120°C on Al⁺- and P⁺-implanted 4H-SiC. The solid-state microwave system used in this study is capable of raising the SiC sample temperatures to extremely high values, at heating rates of ∼600°C∕s. The samples were annealed for 5–60s in a pure nitrogen ambient. Atomic force microscopy performed on the annealed samples indicated a smooth surface with a rms roughness of 1.4nm for 5×5μm² scans even for microwaveannealing at 2050°C for 30s. Auger sputter profiling revealed a <7nm thick surface layer composed primarily of silicon, oxygen, and nitrogen for the samples annealed in N₂, at annealing temperatures up to 2100°C. X-ray photoelectron spectroscopy revealed that this surface layer is mainly composed of silicon oxide and silicon nitride. Secondary ion mass spectrometry depth profiling confirmed almost no dopant in diffusion after microwaveannealing at 2100°C for 15s. However, a sublimation of ∼100nm of the surface SiC layer was observed for 15sannealing at 2100°C. Rutherford backscattering spectra revealed a lattice damage-free SiC material after microwaveannealing at 2050°C for 15s, with scattering yields near the virgin SiC material. Van der Pauw–Hall measurements have revealed sheet resistance values as low as 2.4kΩ∕□ for Al⁺-implanted material annealed at 2100°C for 15s and 14Ω∕□ for the P+-implanted material annealed at 1950°C for 30s. The highest electron and hole mobilities measured in this work were 100 and 6.8cm2/Vs, respectively, for the P⁺- and Al⁺-implanted materials.The GMU work is supported by Army Research Of- fice Dr. Prater under Grant No. W911NF-04-1-0428 and a subcontract from LT Technologies under NSF SBIR Grant No. 0539321

Athermal annealing of Si-implanted GaAs and InP

GaAs and InP crystals ion implanted with Si were athermally annealed by exposing each crystal at a spot of ~2 mm diameter to a high-intensity 1.06 μm wavelength pulsed laser radiation with ~4 J pulse energy for 35 ns in a vacuum chamber. As a result a crater is formed at the irradiated spot. The crater is surrounded by a dark-colored ring-shaped region which is annealed by mechanical energy generated by rapidly expanding hot plasma that formed on the exposed spot. The electrical characteristics of this annealed region are comparable to those of a halogen-lamp annealed sample. No redistribution of impurities due to transient diffusion is observed in the implant tail region. In x-ray diffraction measurements, a high angle side satellite peak due to lattice strain was observed in the crater and near crater regions of the athermally annealed sample in addition to the main Bragg peak that corresponds to the pristine sample. This high angle side satellite peak is not observed in regions away from the crater (≥5 mm from the center of the crater in GaAs)

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

Funding for Open Access provided by the UMD Libraries Open Access Publishing Fund.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 frontside or backside. Morphology, structural, chemical, and optical properties of sputtered NiO and ZnO films were also investigated

Fe and Cr doping of liquid‐phase epitaxial In0.53Ga0.47As/InP

Fe and Cr doping of liquid‐phase epitaxial In0.53Ga0.47As grown at 650 °C on InP substrates have been investigated. Varying amounts of high‐purity Fe and Cr have been added to the growth melt. The resistivity of Fe‐doped layers increases with increase of Fe added to the melt, and layers with ND−NA as low as 2.0×1012 cm−3 can be grown consistently. From analysis of temperature‐dependent Hall data on conducting Fe‐doped samples, the Fe acceptor ionization energy is found to be 0.46 eV. No additional feature is seen in the 4 K band‐edge photoluminescence spectra of Fe‐doped layers. Cr doping seems to produce donorlike behavior and the electron concentration increases monotonically with increased addition of Cr to the melt. An additional peak, separated from the band‐gap energy by 24 meV is seen in the photoluminescence spectra of Cr‐doped samples. It is believed that Cr itself, or a complex defect involving Cr is responsible for the formation of a donorlike center.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71081/2/JAPIAU-57-2-333-1.pd

Recent Advances in Electrochemical Sensors for Detecting Toxic Gases: NO₂, SO₂ and H₂S

Toxic gases, such as NOx, SOx, H2S and other S-containing gases, cause numerous harmful effects on human health even at very low gas concentrations. Reliable detection of various gases in low concentration is mandatory in the fields such as industrial plants, environmental monitoring, air quality assurance, automotive technologies and so on. In this paper, the recent advances in electrochemical sensors for toxic gas detections were reviewed and summarized with a focus on NO2, SO2 and H2S gas sensors. The recent progress of the detection of each of these toxic gases was categorized by the highly explored sensing materials over the past few decades. The important sensing performance parameters like sensitivity/response, response and recovery times at certain gas concentration and operating temperature for different sensor materials and structures have been summarized and tabulated to provide a thorough performance comparison. A novel metric, sensitivity per ppm/response time ratio has been calculated for each sensor in order to compare the overall sensing performance on the same reference. It is found that hybrid materials-based sensors exhibit the highest average ratio for NO2 gas sensing, whereas GaN and metal-oxide based sensors possess the highest ratio for SO2 and H2S gas sensing, respectively. Recently, significant research efforts have been made exploring new sensor materials, such as graphene and its derivatives, transition metal dichalcogenides (TMDs), GaN, metal-metal oxide nanostructures, solid electrolytes and organic materials to detect the above-mentioned toxic gases. In addition, the contemporary progress in SO2 gas sensors based on zeolite and paper and H2S gas sensors based on colorimetric and metal-organic framework (MOF) structures have also been reviewed. Finally, this work reviewed the recent first principle studies on the interaction between gas molecules and novel promising materials like arsenene, borophene, blue phosphorene, GeSe monolayer and germanene. The goal is to understand the surface interaction mechanism