Ilan Ben-Yaacov

AlGaN/GaN current aperture vertical electron transistors with regrown channels

AlGaN/GaN current aperture vertical electron transistors with regrown aperture and source regions have been fabricated and tested. A 2 μm thick GaN:Si drain region followed by a 0.4 μm GaN:Mg current-blocking layer were grown by metalorganic chemical vapor deposition on a c-plane sapphire substrate. Channel apertures were etched, and a maskless regrowth was performed to grow unintentionally doped GaN inside the aperture as well as above the insulating layer, and to add an AlGaN cap layer. Cl2 reactive ion etching was used to pattern the device mesa, and source, drain, and gate metals were then deposited. Devices were achieved with a maximum source-drain current of 750 mA/mm, an extrinsic transconductance of 120 mS/mm, and a 2-terminal gate breakdown of 65 V while exhibiting almost no DC-RF dispersion for 80 μs pulsed I–V curves. The suppression of DC-RF dispersion was shown to result from the absence of the large electric fields at the surface on the drain-side edge of the gate that are present in high el...

CheapStat: An Open-Source, “Do-It-Yourself” Potentiostat for Analytical and Educational Applications

Although potentiostats are the foundation of modern electrochemical research, they have seen relatively little application in resource poor settings, such as undergraduate laboratory courses and the developing world. One reason for the low penetration of potentiostats is their cost, as even the least expensive commercially available laboratory potentiostats sell for more than one thousand dollars. An inexpensive electrochemical workstation could thus prove useful in educational labs, and increase access to electrochemistry-based analytical techniques for food, drug and environmental monitoring. With these motivations in mind, we describe here the CheapStat, an inexpensive (<

Indium-surfactant-assisted growth of high-mobility AlN/GaN multilayer structures by metalorganic chemical vapor deposition

80), open-source (software and hardware), hand-held potentiostat that can be constructed by anyone who is proficient at assembling circuits. This device supports a number of potential waveforms necessary to perform cyclic, square wave, linear sweep and anodic stripping voltammetry. As we demonstrate, it is suitable for a wide range of applications ranging from food- and drug-quality testing to environmental monitoring, rapid DNA detection, and educational exercises. The devices schematics, parts lists, circuit board layout files, sample experiments, and detailed assembly instructions are available in the supporting information and are released under an open hardware license.

Optimization of AlGaN∕GaN current aperture vertical electron transistor (CAVET) fabricated by photoelectrochemical wet etching

AlN/GaN single and multilayer structures with various AlN and GaN layer thicknesses were grown by metalorganic chemical vapor deposition. Step flow growth of AlN was achieved using trimethylindium as a surfactant. Defect formation in the AlN layer could be largely prevented for AlN layers thinner than 2.9 nm. In the multiquantum-well samples, which consisted of five (AlN/GaN) periods, a two-dimensional electron gas (2DEG) was formed at the interface between the GaN base layer and the first AlN barrier layer. When the thickness of the AlN barrier layer in the multiquantum well was increased from 0.9 to 2.6 nm at a constant GaN well thickness of 5 nm, the sheet carrier density of the 2 DEG increased from 5×1012 to 2.1×1013 cm−2 and the electron mobility measured at 77 K decreased from 11780 to 3140 cm2/V s. The effect of the GaN well thickness was also investigated.

AlGaN/GaN current aperture vertical electron transistors

AlGaN∕GaN current aperture vertical electron transistor (CAVET) was fabricated and optimized for band gap selective photoelectrochemical wet etching. The large polarization induced voltage offset (around 2.5–4eV) observed in the first generation CAVET was reduced to 0.7V in this structure by employing a δ Si doping layer buried 60A below the In0.03Ga0.97N (60nm thick) and bottom GaN interface to screen the polarization fields. Other sample structures were studied to achieve an aperture with both good undercut etching and a small voltage offset. It was clearly demonstrated that etch selectivity in the GaN∕InGaN∕GaN undercut structures was influenced by hole confinement and the chemical activity of the N-face GaN.

Indium surfactant assisted growth of AlN/GaN heterostructures by metal-organic chemical vapor deposition

Describes AlGaN/GaN current aperture vertical electron transistor (CAVET) structures. A CAVET consists of a source region separated from a drain region by an insulating layer containing a narrow aperture which is filled with conducting material. A device mesa is formed by reactive ion etching, and source contacts are deposited on either side of the aperture. The drain metal contacts the n-doped region below the aperture. Electrons flow from the source contacts through the aperture into the n-type base region and are collected at the drain. A Schottky gate, located directly above the aperture, is used to modulate the current passing through the aperture. In a CAVET, because the virtual drain (or pinched off region) is located underneath the gate, charge does not accumulate at the gate edge, so no large fields near the gate edge are present. Instead, our simulations show that the high field region in a CAVET is buried in the bulk. The CAVET therefore has the potential to support large source-drain voltages, since surface related breakdown is eliminated.

ETCHED APERTURE GaN CAVET THROUGH PHOTOELECTROCHEMICAL WET ETCHING

AlN/GaN single and multi-layer structures were grown by metal-organic chemical vapor deposition. Step flow growth of AIN was achieved by addition of trimethylindium to the growth ambient, which enhanced the surface mobility of adsorbed Al-species. For AlN/GaN multi-layer structures, electron mobilities of 9900 cm 2 /Vs at a sheet carrier density of 1.2 x 10 13 cm -2 were measured at 77 K, which is significantly higher than the values observed for AlGaN/GaN heterostructures at comparable sheet carrier densities.

Enhancement Mode III-N HEMTs

We describe the fabrication of the CAVET (Current Aperture Vertical Electron Transistor) by Photoelectrochemical (PEC) formation of a current aperture. Etch process is quite naturally critical to the achievement of the etched aperture in CAVET. We provide some background on that etch process, and the subsequent modification and optimization of the process for CAVET fabrication.