Thermal Behavior of an AlGaN/GaN-Based Schottky Barrier Diode on Diamond and Silicon Substrates.

Devices based on AlGaN/GaN heterostructures, for example, Schottky barrier diodes (SBDs) and high electron mobility transistors (HEMTs), have been intensively investigated for applications to high-frequency and high-power areas. Presently, the substrates widely distributed are AlGaN/GaN on SiC for its high performance in radio frequency (RF) applications, for examples high cutoff frequency (fT) or high maximum oscillation frequency (fmax), and AlGaN/GaN on Si for its high power performance, for examples high breakdown voltage or high voltage operation. Chemical vapor deposition (CVD) diamond substrates have a thermal conductivity of 12 W/cm·K, and this is a remarkable point because HEMTs or SBDs on AlGaN/GaN on CVD diamonds are one of the promising alternatives for power and RF applications. In comparison, the thermal conductivity of AlGaN/GaN on a sapphire substrate is 0.33 W/cm·K while that of AlGaN/GaN on a Si substrate is 1.3 W/cm·K and that of AlGaN/GaN on a SiC substrate is 4.9 W/cm·K. In this work, we fabricated SBDs with a 137 mm Schottky channel length on AlGaN/GaN on Si and also on a CVD diamond substrate. We also compared the thermal behaviors of these fabricated large scale SBDs on Si and a CVD diamond substrate.

Effects of Recess Depth Under the Gate Area on the Vth-Shift for Fabricating Normally-Off Field Effect Transistors on AlGaN/GaN Heterostructures.

Fabrication of normally-off field effect transistors (FETs) possessed uniform turn-on threshold voltage (Vth) is of special interests. In this work, they were fabricated using dry etching recess techniques under the gate region, with dry etching conditions of extremely low rate. We report how the recess depth under the gate area induced the Vth shift of normally-off FETs on AlGaN/GaN heterostructure, which were fabricated with a 1.5 nm/min etching rate. Chlorine-based inductively coupled plasma (ICP) was applied to perform the etching process for the AlGaN/GaN heterostructure. Devices were fabricated with different recess depths under the gate area, and examined to determine their performances, particularly the dependence of recess time and recess depth on Vth shift. The applied dry etching conditions resulted in a low-damaged and not-rough morphology on the etched surfaces of AlGaN/GaN. Fine controlled and well defined recess depth of the AlGaN/GaN heterostructure under the gate region was achieved with no etch-stop layers. Conventional fabrication processes were applied with the dry etching conditions of extremely low rate to fabricate normally-off MOSFETs of Al2O3/AlGaN/GaN. The achieved Vth of +5.64 V was high positive and the leakage current of off-state was measured as ~10-6 A/mm.

Thermal Properties of Schottky Barrier Diode on AlGaN/GaN Heterostructures on Chemical Vapor Deposition Diamond.

High electron mobility transistors (HEMTs) and Schottky barrier diodes (SBDs) based on AlGaN/GaN heterostructure have been widely studied for high-frequency and/or high-power application. Widely distributed substrates for the high performance of RF applications are presently AlGaN/GaN on SiC, and those for high power performance are AlGaN/GaN on Si. Because the thermal conductivity of CVD diamond substrates is as high as 12 W/cm · K, devices on AlGaN/GaN on CVD diamond are one of the excellent alternatives for power and RF applications. In comparison, the thermal conductivity of AlGaN/GaN on SiC is 4.9 W/cm K, and that of AlGaN/GaN on Si is 1.3 W/cm · K. In this work, we report the fabrication of SBD devices with 163.8 mm Schottky channel length. We also compared the thermal properties of the fabricated large scale SBD devices on different substrates.

Biotin-functionalized semiconducting polymer in an organic field effect transistor and application as a biosensor.

This report presents biotin-functionalized semiconducting polymers that are based on fluorene and bithiophene co-polymers (F8T2). Also presented is the application of these polymers to an organic thin film transistor used as a biosensor. The side chains of fluorene were partially biotinylated after the esterification of the biotin with corresponding alcohol-groups at the side chain in F8T2. Their properties as an organic semiconductor were tested using an organic thin film transistor (OTFT) and were found to show typical p-type semiconductor curves. The functionality of this biosensor in the sensing of biologically active molecules such as avidin in comparison with bovine serum albumin (BSA) was established through a selective decrease in the conductivity of the transistor, as measured with a device that was developed by the authors. Changes to the optical properties of this polymer were also measured through the change in the color of the UV-fluorescence before and after a reaction with avidin or BSA.