The surface preparation for depositing Al 2 O 3 for fabricating Au/Ni/Al 2 O 3 /n-GaN (0001) metal oxide semiconductor (MOS) capacitors was optimized as a step toward realization of high performance GaN MOSFETs. The GaN surface treatments studied included cleaning with piranha (H 2 O 2 :H 2 SO 4 ¼ 1:5), (NH 4 ) 2 S, and 30% HF etches. By several metrics, the MOS capacitor with the piranha-etched GaN had the best characteristics. It had the lowest capacitance-voltage hysteresis, the smoothest Al 2 O 3 surface as determined by atomic force microscopy (0.2 nm surface roughness), the lowest carbon concentration ($0.78%) at the Al 2 O 3 /n-GaN interface (from x-ray photoelectron spectroscopy), and the lowest oxide-trap charge (Q T ¼ 1.6 Â 10 11 cm À2 eV À1

This paper reports on the influence of deposition temperature on the structure, composition, and electrical properties of TiO 2 thin films deposited on n-type silicon (100) by plasma-assisted atomic layer deposition (PA-ALD). TiO 2 layers ∼20 nm thick, deposited at temperatures ranging from 100 to 300 • C, were investigated. Samples deposited at 200 • C and 250 • C had the most uniform coverage as determined by atomic force microscopy. The average carbon concentration throughout the oxide layer and at the TiO 2 /Si interface was lowest at 200 • C. Metal oxide semiconductor capacitors (MOSCAPs) were fabricated, and profiled by capacitance-voltage techniques. The sample prepared at 200 • C had negligible hysteresis (from a capacitance-voltage plot) and the lowest interface trap density (as extracted using the conductance method). Current-voltage measurements were carried out with top-to-bottom structures. At −2 V gate bias voltage, the smallest leakage current was 1.22 × 10 −5 A/cm 2 for the 100 9 and smaller leakage current density are highly desirable. The insulator deposition temperatures should be below 500• C, because capacitors are expected to be deposited after transistors formation.10 However, further research on the high dielectric materials is needed to fulfill those requirements.In the present study, plasma-assisted atomic layer deposition (PA-ALD) was employed to deposit thin insulating TiO 2 films, because it offers excellent atomic level control of layer thickness with good uniformity and conformality.11 With an O 2 plasma, the deposition can be conducted at a lower temperature and with a shorter purge time in cold-wall reactors than a conventional thermal ALD system. 12These characteristics are particularly suitable for growing capacitor dielectrics for use in DRAM, as it uses a three dimensional structure with a high aspect ratio to increase the effective surface area. 13The present work reports on the impact of the deposition temperature on the properties of TiO 2 films prepared by PA-ALD and on the performance of said films in silicon MOSCAPs. By correlating the oxide structure, surface morphology and impurity concentration with electrical properties (hysteresis, interface trap density and leakage current), an optimal deposition temperature is identified. ExperimentalTiO 2 ALD Film growth and metal contact deposition.-Before deposition, the n-type Si (100) substrates were cleaned with acetone and isopropyl alcohol (IPA) for 5 minutes at 40• C. TiO 2 was deposited by PA-ALD in an Oxford Instruments FlexAL ALD reactor with tetrakisdimethylamino titanium (TDMAT) kept at 39• C as the titanium precursor, and oxygen plasma as the oxidizing agent. The ALD growth temperatures were 100• C, 150• C and 300• C. All ALD depositions consisted of 400 cycles and each ALD cycle included a 0.4 second dose of TDMAT followed by a 4 second * Electrochemical Society Active Member.z E-mail: edgarjh@ksu.edu purge with Ar gas, and a 3 second exposure to the oxygen plasma followed by a 3 second purge. The plasma power and...

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The benefits of dry oxidation of n ‐GaN for the fabrication of metal‐oxide‐semiconductor structures are reported. GaN thin films grown on sapphire by MOCVD were thermally oxidized for 30, 45 and 60 minutes in a pure oxygen atmosphere at 850 °C to produce thin, smooth GaOx layers. The GaN sample oxidized for 30 minutes had the best properties. Its surface roughness (0.595 nm) as measured by atomic force microscopy (AFM) was the lowest. Capacitance‐voltage measurements showed it had the best saturation in accumulation region and the sharpest transition from accumulation to depletion regions. Under gate voltage sweep, capacitance‐voltage hysteresis was completely absent. The interface trap density was minimum (Dit = 2.75×1010 cm–2eV–1) for sample oxidized for 30 mins. These results demonstrate a high quality GaOx layer is beneficial for GaN MOSFETs. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

This study compares the physical, chemical and electrical properties of Al2O3 thin films deposited on gallium polar c‐ and nonpolar m ‐plane GaN substrates by atomic layer deposition (ALD). Correlations were sought between the film's structure, composition, and electrical properties. The thickness of the Al2O3 films was 19.2 nm as determined from a Si witness sample by spectroscopic ellipsometry. The gate dielectric was slightly aluminum‐rich (Al:O=1:1.3) as measured from X‐ray photoelectron spectroscopy (XPS) depth profile, and the oxide‐semiconductor interface carbon concentration was lower on c ‐plane GaN. The oxide's surface morphology was similar on both substrates, but was smoothest on c ‐plane GaN as determined by atomic force microscopy (AFM). Circular capacitors (50‐300 μm diameter) with Ni/Au (20/100 nm) metal contacts on top of the oxide were created by standard photolithography and e‐beam evaporation methods to form metal‐oxide‐semiconductor capacitors (MOSCAPs). The alumina deposited on c ‐plane GaN showed less hysteresis (0.15 V) than on m ‐plane GaN (0.24 V) in capacitance‐voltage (CV) characteristics, consistent with its better quality of this dielectric as evidenced by negligible carbon contamination and smooth oxide surface. These results demonstrate the promising potential of ALD Al2O3 on c ‐plane GaN, but further optimization of ALD is required to realize the best properties of Al2O3 on m ‐plane GaN. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)