Salih Saygi

AlGaN/InGaN/GaN Double Heterostructure Field-Effect Transistor

Novel, current collapse free, double heterostructure AlGaN/InGaN/GaN field effect transistors (DHFETs) are fabricated on the insulating SiC substrates. The simulations show that a combined effect of the bandgap offsets and polarization charges provides an excellent 2D carrier confinement. These devices demonstrate output RF powers as high as 4.3 W/mm in CW mode and 6.3 W/mm in the pulsed mode, with the gain compression as low as 4 dB.

Submicron gate Si 3 N 4 /AlGaN/GaN-metal-insulator-semiconductor heterostructure field-effect transistors

We present the characteristics of a quarter-micron gate metal-insulator-semiconductor heterostructure field-effect transistor (MISHFET) with Si/sub 3/N/sub 4/ film as a gate insulator. A detailed comparison of the MISHFET and an identical geometry HFET shows them to have the same radio frequency (RF) power gain and cut-off frequency, while the MISHFET has much lower gate-leakage currents and higher RF powers at operating frequencies as high as 26 GHz. The MISHFET gate-leakage currents are well below 100 pA at gate bias values from -10 V to +8 V. At zero gate bias, the drain saturation current is about 0.9 A/mm and it increases to 1.2 A/mm at +8 V gate bias. The output RF power of around 6 W/mm at 40 drain bias was found to be frequency independent in the range of 2 to 26 GHz. This power is 3 dB higher than that from HFET of the same geometry. The intrinsic cutoff frequency is /spl sim/63 GHz for both the HFET and the MISHFET. This corresponds to an average effective electron velocity in the MISHFET channel of 9.9/spl times/10/sup 6/ cm/s. The knee voltage and current saturation mechanisms in submicron MISHFETs and heterostructure field-effect transistors (HFET) are also discussed.

Real-Space Electron Transfer in III-Nitride Metal-Oxide-Semiconductor-Heterojunction Structures

The real-space transfer effect in a SiO2∕AlGaN∕GaN metal-oxide-semiconductor heterostructure (MOSH) from the two-dimensional (2D) electron gas at the heterointerface to the oxide-semiconductor interface has been demonstrated and explained. The effect occurs at high positive gate bias and manifests itself as an additional step in the capacitance-voltage (C‐V) characteristic. The real-space transfer effect limits the achievable maximum 2D electron gas density in the device channel. We show that in MOSH structures the maximum electron gas density exceeds up to two times that at the equilibrium (zero bias) condition. Correspondingly, a significant increase in the maximum channel current (up to two times compared to conventional Schottky-gate structures) can be achieved. The real-space charge transfer effect in MOSH structures also opens up a way to design novel devices such as variable capacitors, multistate switches, memory cells, etc.

Superconductivity in nanostructured lead

Abstract Three-dimensional nanoscale structures of lead were fabricated by electrodeposition of pure lead into artificial porous opal. The size of the metallic regions was comparable to the superconducting coherence length of bulk lead. T c as high as 7.36 K was observed, also d T c /d H was 2.7 times smaller than in bulk lead. Many of the characteristics of these differ from bulk lead, a type I superconductor. Irreversibility line and magnetic relaxation rates ( S ) were also studied. S ( T ) displayed two maxima, with a peak value about 10 times smaller than that of typical high- T c superconductors.

Insulated gate III-N devices and ICs

The MOSHFET design which combines the advantage of the MOS structure, which suppresses the gate leakage current, and an AlGaN/GaN heterointerface that provides high density, high mobility two-dimensional electron gas channel. This article presents a comparative review of the I-V characteristics, cut-off frequencies, RF output powers, power gain, and nonlinear distortions of AlGaN/GaN MOSHFET, and HFET device. The MOSHFETs possess significant advantages for the monolitic IC design. They sustain very high input impedance at elevated temperatures, even above 300 /spl deg/C. The results show that the MOSHFET based ICs are extremely promising for a large variety of high-power high-temperature applications.