Search

Off-state breakdown characteristics of AlGaN/GaN high-electron-mobility transistors have been studied based on drain current injection method. It is found that at low drain current injection level, the observed premature breakdown is caused by excess gate-to-drain leakage current. Nevertheless, at high drain injection current level, buffer-leakage-dominated breakdown proceeds gate-leakage-dominated breakdown as the gate bias increases from pinch-off voltage to deep-depletion voltage. In both breakdown regions, the breakdown voltages show negative temperature coefficients. The buffer-leakage-induced breakdown should be defect-related, which is confirmed by temperature-dependent buffer leakage measurements. [ABSTRACT FROM AUTHOR]

A gate-induced-drain-leakage-induced off-state breakdown is examined in our high-voltage depletion-mode n-channel metal–oxide–semiconductor field-effect transistors. By increasing the dosage in the n-region, a bell-shaped trend between the off-state breakdown voltage VBD and the dosage in the n-region is observed. Such a bell-shaped trend is found to result from two competing factors: an electric field in the gate edge and an electric field associated with the drain–bulk junction. The latter electric field is responsible for the falling part in the bell-shaped trend. Our model can explain the data of the slightly bell-shaped trend between off-state VBD and implant energy in the n-region. Additionally, the effect of Si recess variation on off-state VBD variation can be understood from our model. According to our model, approaches to improve off-state VBD and the effect of Si recess variation on VBD variation are proposed. [ABSTRACT FROM PUBLISHER]

Improvement of the AlGaN/GaN high-electron mobility transistor's (HEMT's) off -state breakdown voltage is achieved by implanting ^19\F^+ ions at an energy of 50 keV and dose of \1 \times \10^12\ \cm^-2 under the gate region using \BF3 as the source. The charge state of the implanted fluorine ions changes from positive to negative in the AlGaN/GaN structure because of fluorine's strong electronegativity. The negative-charged fluorine ions at the back side of the two-dimensional electron gas can raise the energy barrier of the GaN buffer layer under the channel, effectively blocking the current injected from the source to the high-field region of the GaN channel when the HEMT is biased at off-state. The source-injected electrons, if not blocked, could flow to the high-field region and initiate a premature three-terminal off-state breakdown in a conventional AlGaN/GaN HEMT. A 38% improvement of the three-terminal off-state breakdown voltage and 40% improvement of the power figure-of-merit VBD-off^2/Ron are achieved in the enhanced back barrier HEMT. [ABSTRACT FROM AUTHOR]

Design considerations and performance of n++ GaN/InAlN/AlN/GaN normally off high-electron mobility transistors (HEMTs) are analyzed. Selective and damage-free dry etching of the gate recess through the GaN cap down to a 1-nm-thick InAlN barrier secures positive threshold voltage, while the thickness and the doping of the GaN cap influence the HEMT direct current and microwave performance. The cap doping density was suggested to be 2 x 1020 cm-3. To screen the channel from the surface traps, the needed cap thickness was estimated to be only 6 nm. Design is proved by an experiment showing a constant value of the HEMT dynamical access resistance, while a single-pulse experiment indicated almost collapse-free performance. On the other hand, it is found that the n++ GaN cap does not contribute to the HEMT drain current conduction, nor does it provide a path for the OFF-state breakdown. HEMTs with a gate length of 0.25 µm and a 4-&um;m source-to-drain distance show a drain-to-source current of 0.8 A/mm, a transconductance of 440 mS/mm, a threshold voltage of ~0.4 V, and a cutoff frequency of 50 GHz. A thin and highly doped GaN cap is also found to be suitable for the processing of normally on HEMTs by adopting the nonrecessed gate separated from the cap by insulation. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high-electron mobility transistor's (HEMT's) off-state breakdown is investigated using drain-current injection techniques with different injection current levels. Competitions between the source leakage and gate leakage, pure leakage and impact ionization, and source- and gate-injection-induced impact ionization during the drain-injection measurement are discussed in detail. It was found that the breakdown originates from the source/gate leakage at low drain injection levels but is dominated by source/gate-induced impact ionization process at high drain injection currents. The source-induced impact ionization usually precedes the gate-induced impact ionization in low-gate leakage devices, resulting in a premature three-terminal off-state breakdown. We also found that the gate-bias value affects the breakdown voltage in the conventional three-terminal off-state breakdown I-V measurement and should be carefully considered. [ABSTRACT FROM AUTHOR]

Abstract: Pseudomorphic high electron mobility transistors (pHEMTs) were applied to cover an extremely wide frequency range. The pHEMT structure combined with the hydrogen sensor concept was fabricated and simulated. The remarkable saturation current density explained that the sensor was suitable for operation at room temperature. In addition, the Schottky barrier height lowered was demonstrated. From the experimental and simulated data, it was found that not only the Schottky barrier height lowering but also the change of the conduction-band discontinuity (ΔE C) in a hydrogen-containing ambience influenced the characteristics of the hydrogen sensor. The related threshold voltage change of the hydrogen sensor was also manifested. Furthermore, two important parameters of pHEMT, i.e., on-state output drain current and off-state breakdown characteristics, under exposing to a hydrogen ambience were also discussed. The studied device was shown to be a candidate for a high-power and highly sensitive hydrogen sensor and pHEMT integrated circuit applications. [Copyright &y& Elsevier]

The reversible breakdown walkout in the Si3N4 passivated AlGaAs/InGaAs pseudomorphic high-electron mobility transistors (PHEMTs) has been observed and investigated. Due to the double passivation processes, the fabricated PHEMTs demonstrated the reversible off-state breakdown walkout without changing device dc and RF performance significantly. This reversible breakdown behavior was induced by on-state stress. By repeating off-state and on-state stress, the breakdown voltages (VBs) eventually reached "stable region" or "reverse region" depending on the final stress process. A 2 V difference was observed between these two regions of breakdown. [ABSTRACT FROM PUBLISHER]

This paper reviews the literature dealing with off-state gate-drain breakdown in MESFET and HEMT structures, with particular emphasis on GaAs PHEMTs, in terms of: 1) the physics of the breakdown phenomenon; 2) the breakdown walkout effect; 3) the impact of design and process choices on the breakdown behavior; and 4) the experimental techniques used for breakdown characterization. A thorough temperature-dependent breakdown characterization of commercial PHEMTs is also shown and discussed. It is found that different physical mechanisms may dominate the gate-drain leakage depending on the reverse bias and temperature range considered, and the particular PHEMT technology. The main results shown here tell us the following. 1) The breakdown voltages are decreasing functions of temperature between room temperature and 160°C. 2) Between room temperature and 90-100°C, thermionic-field emission seems be dominant, with low activation energies below 0.15 eV; as a consequence, the temperature dependence of the breakdown voltage is weak. 3) Between 110°C and 160°C, higher activation energy mechanisms (possibly trap-assisted tunneling and thermionic emission over a field-dependent barrier) tend to dominate, and the temperature dependence of the breakdown voltages is stronger. [ABSTRACT FROM PUBLISHER]