We report on a GaN metal-oxide-semiconductor high-electron-mobility-transistor ͑MOS-HEMT͒ using atomic-layer-deposited ͑ALD͒ Al 2 O 3 as the gate dielectric. Compared to a conventional GaN high-electron-mobility-transistor ͑HEMT͒ of similar design, the MOS-HEMT exhibits several orders of magnitude lower gate leakage and several times higher breakdown voltage and channel current. This implies that the ALD Al 2 O 3 /AlGaN interface is of high quality and the ALD Al 2 O 3 /AlGaN/GaN MOS-HEMT is of high potential for high-power rf applications. In addition, the high-quality ALD Al 2 O 3 gate dielectric allows the effective two-dimensional ͑2D͒ electron mobility at the AlGaN/GaN heterojunction to be measured under a high transverse field. The resulting effective 2D electron mobility is much higher than that typical of Si, GaAs or InGaAs metal-oxide-semiconductor field-effect-transistors ͑MOSFETs͒.One of the major factors that limit the performance and reliability of GaN high-electron-mobility-transistors ͑HEMTs͒ for high-power radio-frequency ͑rf͒ applications is their relatively high gate leakage. The gate leakage reduces the breakdown voltage and the power-added efficiency while increasing the noise figure. To help solve the problem, significant progress has been made on metal-insulatorsemiconductor high-electron-mobility-transistors ͑MIS-HEMTs͒ and metal-oxide-semiconductor high-electronmobility-transistors ͑MOS-HEMTs͒ using SiO 2 , 1-5 Si 3 N 4 , 6,7 Al 2 O 3 8,9 ͑formed by electron cyclotron resonance plasma oxidation of Al͒, and other oxides. 10 However these gate dielectrics and their associated processes may not be readily scalable for low-cost and high-yield manufacture. Atomic layer deposition ͑ALD͒ is a surface controlled layer-by-layer process for the deposition of thin films with atomic layer accuracy. Each atomic layer formed in the sequential process is a result of saturated surface controlled chemical reactions. The thickness control of the ALD films thus scalability is much superior than those of the plasma-enhanced-chemicalvapor-deposition ͑PECVD͒ grown SiO 2 and Si 3 N 4 . The quality of the ALD Al 2 O 3 is also much higher than those deposited by other methods, i.e., sputtering and electron-beam deposition, in terms of uniformity, defect density and stoichiometric ratio of the films.In this letter, we report on a GaN MOS-HEMT with atomic-layer-deposited Al 2 O 3 as the gate dielectric. Similar to SiO

Using a first-principles approach to the ionization rate, we re-examine some of the prejudices concerning impact ionization and offer a new view of the role of thresholds. We also discuss trends of ionization coefficients related to the energy band structure for silicon and a number of III-V compounds.

Articles you may be interested inEffect of indium concentration on InGaAs channel metal-oxide-semiconductor field-effect transistors with atomic layer deposited gate dielectric J. Vac. Sci. Technol. B 29, 040601 (2011); 10.1116/1.3597199 Metal-oxide-semiconductor field-effect transistors on GaAs (111)A surface with atomic-layer-deposited Al 2 O 3 as gate dielectrics

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Recently, significant progress has been made on GaAs metal-oxide-semiconductor field-effect transistors ͑MOSFETs͒ using atomic-layer deposition ͑ALD͒-grown Al 2 O 3 as gate dielectric. We show here that further improvement can be achieved by inserting a thin In 0.2 Ga 0.8 As layer as part of the channel between Al 2 O 3 and GaAs channel. A 1-m-gate-length, depletion-mode, n-channel In 0.2 Ga 0.8 As/GaAs MOSFET with an Al 2 O 3 gate oxide of 160 Å shows a gate leakage current density less than 10 Ϫ4 A/cm 2 , a maximum transconductance ϳ105 mS/mm, and a strong accumulation current at V gs Ͼ0 in addition to buried-channel conduction. Together with longer gate-length devices, we deduce electron accumulation surface mobility for In 0.2 Ga 0.8 As as high as 660 cm 2 /V s at Al 2 O 3 /In 0.2 Ga 0.8 As interface.

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Using high-sensitivity confocal time-resolved photoluminescence (PL) techniques, we report an ultrafast PL (40 ps–5 ns) from impurity-free surface flaws on fused silica, including polished, indented, or fractured surfaces of fused silica, and from laser-heated evaporation pits. This PL is excited by the single-photon absorption of sub-band gap light, and is especially bright in fractures. Regions which exhibit this PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 3.5 eV nanosecond-scale laser pulses.