The influence of the InGaN back-barrier on the properties of Al

This is a theoretical study of the InGaN back-barrier on the properties of the Al03Ga0.7N/AlN/GaN/InGaN/GaN HEMT structure by self-consistently solving coupled Schrödinger and Poisson equations. Our calculation shows that by increasing the indium composition, the conduction band of the GaN buffer layer is raised and the confinement of 2DEG is improved. However, the additional quantum well formed by InGaN becomes deeper, inducing and confining more electrons in it. Another conductive channel is formed which may impair the device performance. With the increasing InGaN thickness, the well depth remains the same and the conduction band of GaN buffer layer rises, enhancing the confinement of the 2DEG without inducing more electrons in the well. The 2DEG sheet density decreases slightly with the indium composition and the physical mechanism is discussed. Low indium composition and thick InGaN back-barrier layer are beneficial to mitigate the short-channel effects, especially for high-frequency devices

A lanthanide-based magnetic nanosensor as an erasable and visible platform for multi-color point-of-care detection of multiple targets and the potential application by smartphone

The sensitive, selective and point-of-care detection of dipicolinic acid (DPA) is of great significance for the prevention of the anthrax virus and the containment of bioterrorism. In this work, a multi-color fluorescent nanoprobe composed of lanthanides and magnetic nanoparticles (Fe3O4@CePO4:Tb-EDTA-Eu) has been designed, in which the portion of Fe3O4@CePO4:Tb can be used as the internal stable signal of green fluorescence, while the EDTA-Eu part can be used as the sensitive reaction signal for monitoring DPA. Upon the addition of DPA, the red fluorescence of Eu3+ ions is significantly enhanced, while the fluorescent color of the nanoprobes can change from green to red (such as yellow-green, orange-yellow and orange-red), achieving visual multi-color fluorescent detection even by the naked eye. By using the magnetic separation method, the composites can be easily purified for point-of-care testing. More importantly, the nanoprobe fixed test pieces enable real-time analysis of DPA by using an easy-to-access color-scanning application on a smartphone. Furthermore, the fluorescence intensity can be quenched by the addition of Cu2+, which leads to a rewritable nanosensor and can be used in the detection of cysteine (Cys) with high sensitivity. With the addition of Cys, this erasable nano detection platform can also display the original multi-color visual point-of-care detection. With further optimization, this new type of multi-color fluorescent assay is promising in point-of-care clinics for multi-target diagnostics.Jun Xu, Xiao-Ke Shen, Lei Jia, Jian-Liang Cao, Yan Wang, Xiao-Lei Zhao, Ning Bi, Sheng-Li Guoa and Tian-Yi M

The influence of pressure on the growth of InAlN/AlN/GaN heterostructure

The influence of pressure on the MOCVD grown InAlN/AlN/GaN heterostructure has been investigated by high-resolution X-ray diffraction, Hall measurement and atomic force microscopy. High pressure is beneficial to increase indium incorporation efficiency. The electrical properties of InAlN/AlN/GaN heterostructure become better with the pressure decreasing from 100 Torr to 50 Torr. Indium droplets tend to form on the InAlN surface at high pressure. The edge of the indium droplet is the Al-rich region while the interior is the In-rich region, demonstrated by the phase-contrast mode. Phase contrast across the V-defect is strong on the surface of InAlN grown at low pressure (50 Torr) whereas it is not evident at high pressure (100 Torr), indicating that large stress in the InAlN film will enhance the compositional variation

Low temperature characteristics of AlGaN/GaN high electron mobility transistors

The I-V characteristics of AlGaN/GaN high electron mobility transistors in the temperature range between 100 K and 300 K are studied. It is found that both the maximum drain-source current and transconductance decrease with the increase of temperature. Decrease of the electron mobility with increasing temperature is considered to be the main cause for that condition. The threshold voltage shows a forward shift, which can be explained by the increase of Schottky barrier with increasing temperature. It is found that at VGS = 0 V the drain-source current reduces with the ascending temperature, which should be due to the variation of the electron mobility with the temperature. While at VGS = −5 V the drain-source current is found to increase with the ascending temperature, it is suggested to be caused by the positive temperature coefficient of the electron transport in the depleted region

The transport mechanism of gate leakage current in AlGaN/GaN high electron mobility transistors

The temperature dependence of the I-V characteristics on Au/Ni-HEMT Schottky contacts was measured and analyzed. Large deviations from the thermionic emission and thermionic-field emission model were observed in the I-V-T characteristics. The thin surface barrier model only fits the measured curves in the high bias region, but deviates drastically in the low bias region. Using a revised thin surface barrier model, the calculated curves match well with the measured curves. It is also found that tunneling emission model is the dominant current transport mechanism at low temperature, yet thermionic-field emission model is the dominant current transport mechanism at high temperature