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Register a new userImproved Gate Reliability of p-GaN Gate HEMTs by Gate Doping Engineering
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We present a novel p-GaN gate HEMT structure with reduced hole concentration near the Schottky interface by doping engineering in MOCVD, which aims at lowering the electric field across the gate. By employing an additional unintentionally doped GaN layer, the gate leakage current is suppressed and the gate breakdown voltage is boosted from 10.6 to 14.6 V with negligible influence on the threshold voltage and on-resistance. Time-dependent gate breakdown measurements reveal that the maximum gate drive voltage increases from 6.2 to 10.6 V for a 10-year lifetime with a 1% gate failure rate. This method effectively expands the operating voltage margin of the p-GaN gate HEMTs without any other additional process steps.
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We report on the interfacial electronic properties of HfO2 gate dielectrics both, with GaN towards normally-OFF recessed HEMT architectures and the AlGaN barrier for normally-ON AlGaN/GaN MISHEMTs for GaN device platforms on Si. A conduction band offset of 1.9 eV is extracted for HfO2/GaN along with a very low density of fixed bulk and interfacial charges. Conductance measurements on HfO2/GaN MOSCAPs reveal an interface trap state continuum with a density of 9.37x1012 eV-1cm-2 centered at 0.48 eV below EC. The forward and reverse current densities are shown to be governed by Fowler-Nordheim tunneling and Poole-Frenkel emission respectively. Normally-ON HfO2/AlGaN/GaN MISHEMTs exhibit negligible shifts in threshold voltage, transconductances of 110mS/mm for 3 {mu}m gate length devices, and three-terminal OFF-state gate leakage currents of 20 nA/mm at a VD of 100 V. Dynamic capacitance dispersion measurements show two peaks at the AlGaN/GaN interface corresponding to slow and fast interface traps with a peak Dit of 5.5x1013 eV-1cm-2 and 1.5x1013 eV-1cm-2 at trap levels 0.55 eV and 0.46 eV below EC respectively. The HfO2/AlGaN interface exhibits a peak Dit of 4.4x1013 eV-1cm- 2 at 0.45 eV below EC.
An analysis of recent experimental data for high-performance In0.7Ga0.3As high electron mobility transistors (HEMTs) is presented. Using a fully quantum mechanical, ballistic model, we simulate In0.7Ga0.3As HEMTs with gate lengths of LG = 60nm, 85, and 135 nm and compare the result to the measured I-V characteristics including draininduced barrier lowering, sub-threshold swing, and threshold voltage variation with gate insulator thickness, as well as on-current performance. To first order, devices with three different oxide thicknesses and channel lengths can all be described by our ballistic model with appropriate values of parasitic series resistance. For high gate voltages, however, the ballistic simulations consistently overestimate the measured on-current, and they do not show the experimentally observed decrease in on-current with increasing gate length. With no parasitic series resistance at all, the simulated on-current of the LG = 60 nm device is about twice the measured current. According to the simulation, the estimated ballistic carrier injection velocity for this device is about 2.7 x 10^7 cm/s. Because of the importance of the semiconductor capacitance, the simulated gate capacitance is about 2.5 times less than the insulator capacitance. Possible causes of the transconductance degradation observed under high gate voltages in these devices are also explored. In addition to a possible gate-voltage dependent scattering mechanism, the limited ability of the source to supply carriers to the channel, and the effect of nonparabolicity are likely to play a role. The drop in on-current with increasing gate length is an indication that the devices operate below the ballistic limit.
We present a simple fabrication technique for lateral nanowire wrap-gate devices with high capacitive coupling and field-effect mobility. Our process uses e-beam lithography with a single resist-spinning step, and does not require chemical etching. We measure, in the temperature range 1.5-250 K, a subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 $cm^2/Vs$ -- significantly larger than previously reported lateral wrap-gate devices. At depletion, the barrier height due to the gated region is proportional to applied wrap-gate voltage.
Voltage control of interfacial magnetism has been greatly highlighted in spintronics research for many years, as it might enable ultra-low power technologies. Among few suggested approaches, magneto-ionic control of magnetism has demonstrated large modulation of magnetic anisotropy. Moreover, the recent demonstration of magneto-ionic devices using hydrogen ions presented relatively fast magnetization toggle switching, tsw ~ 100 ms, at room temperature. However, the operation speed may need to be significantly improved to be used for modern electronic devices. Here, we demonstrate that the speed of proton-induced magnetization toggle switching largely depends on proton-conducting oxides. We achieve ~1 ms reliable (> 103 cycles) switching using yttria-stabilized zirconia (YSZ), which is ~ 100 times faster than the state-of-the-art magneto-ionic devices reported to date at room temperature. Our results suggest further engineering of the proton-conducting materials could bring substantial improvement that may enable new low-power computing scheme based on magneto-ionics.
We report on experimental studies of terahertz (THz) radiation transmission through grating-gate graphene-channel transistor nanostructures and demonstrate room temperature THz radiation amplification stimulated by current-driven plasmon excitations. Specifically, with increase of the direct current (dc) under periodic charge density modulation, we observe a strong red shift of the resonant THz plasmon absorption, its complete bleaching, followed by the amplification and blue shift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. We present a simple model allowing for the phenomenological description of the observed amplification phenomena. This model shows that in the presence of dc current the radiation-induced correction to dissipation is sensitive to the phase shift between THz oscillations of carrier density and drift velocity, and with increase of the current becomes negative, leading to amplification. The experimental results of this work as all obtained at room temperature, pave the way towards the new 2D plasmons based, voltage tuneable THz radiation amplifiers.
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