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

Area-selective atomic layer deposition (ALD) of lead sulfide (PbS) was achieved on octadecyltrichlorosilane (ODTS)-patterned silicon substrates. We investigated the capability of ODTS self-assembled monolayers (SAMs) to deactivate the ALD PbS surface reactions as a function of dipping time in ODTS solution. The reaction mechanism was investigated using density functional theory (DFT), which showed that the initial ALD half-reaction is energetically unfavorable on a methyl-terminated SAM surface. Conventional photolithography was used to create oxide patterns on which ODTS SAMs were selectively grown. Consequently, PbS thin films were grown selectively only where ODTS was not present, whereas deposition was blocked in regions where ODTS was grown. The resulting fabricated patterns were characterized by scanning electron microscopy and Auger electron spectroscopy, which demonstrated that ALD PbS was well confined to defined patterns with high selectivity by ODTS SAMs. In addition, AFM lithography was employed to create nanoscale PbS patterns. Our results show that this method can be applied to various device-fabrication processes, presenting new opportunities for various nanofabrication schemes and manifesting the benefits of self-assembly.

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