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Al 2 O 3 films have been deposited on n-type and p-type 4H-SiC by atomic layer chemical vapor deposition using trimethylaluminum as a precursor for aluminum and both H2O and O3 as an oxidant. After oxide deposition, annealing at different temperatures (800, 900, 1000°C) in argon atmosphere for different durations (1, 2, 3h) was performed. Bulk and interface properties of the oxide films were studied by capacitance-voltage, current-voltage, deep level transient spectroscopy, and thermally dielectric relaxation current (TDRC) measurements. The results reveal a decreasing flatband voltage with increasing annealing time, suggesting decrease of oxide charges and deep interface traps. After 3h annealing at 1000°C of the n-type samples, the flatband voltage is reduced to 6V compared to a value in excess of 40V for as-deposited samples. The TDRC measurements on annealed Al2O3∕SiC (n-type) capacitors showed substantially different spectra relative to conventional SiO2∕4H-SiC control samples; in the former ones no signal was recorded at temperatures less than 100K, demonstrating a low density of shallow electron traps below the conduction band edge of 4H-SiC and hence a prospect of obtaining a high electron channel mobility in 4H-SiC metal-oxide-semiconductor field-effect devices with Al2O3 as gate dielectric.

Al 2 O 3 films with different thicknesses have been deposited on n-type ͑nitrogen-doped͒ 4H-SiC͑0001͒ epitaxial samples by atomic layer chemical vapor deposition at 300°C and subsequently annealed in Ar atmosphere at temperatures up to 1000°C. The Al 2 O 3 /4H-SiC structures were analyzed by x-ray photoelectron spectroscopy ͑XPS͒, secondary ion mass spectrometry ͑SIMS͒, and transmission electron microscopy ͑TEM͒. The XPS and SIMS results indicate that the average composition in the wider interface area does not significantly change due to the annealing. However, as revealed by the TEM investigations in combination with XPS, the as-grown samples exhibit a double interface created by an intermediate suboxide SiO Because of its wide band gap ͑ϳ3.2 eV for polytype 4H͒, SiC is suitable for applications related to high power, high frequency, and high temperatures. In recent years, investigations for alternative dielectrics for device applications have become of great interest. Al 2 O 3 is one of the few pure metal oxides exhibiting a high dielectric constant ͑ ϳ 10͒, a relatively wide band gap ͑E g ϳ 6.2 eV͒, and a good thermal stability; moreover, compared to ZrO 2 or HfO 2 it displays higher conduction and valence band offsets, ⌬E c = 1.7 eV and ⌬E v = 1.2 eV, relative to 4H-SiC. 1,2 It has been shown that high quality Al 2 O 3 films can be grown on SiC by atomic layer chemical vapor deposition ͑ALCVD͒. 3 In previous studies, 4-6 electrical characterization such as capacitancevoltage ͑CV͒ and thermal dielectric relaxation current measurements of Al 2 O 3 /4H-SiC capacitors were reported. In fact, annealing in Ar above the crystallization temperature ͑ϳ900°C͒ was found to significantly enhance the electrical properties of the Al 2 O 3 / SiC interface and promote formation of the ␥ phase of Al 2 O 3 . Furthermore, it has been revealed that the interface properties of those annealed structures are superior to the ones of SiO 2 /4H-SiC interfaces, since the density of electron traps close to the conduction band minimum is reduced, 4 as required for improved channel mobility in a metal-oxide-SiC field effect transistors. In this study, the Al 2 O 3 /4H-SiC interface was investigated on as-grown and annealed samples using angle resolved x-ray photoelectron spectroscopy ͑AR-XPS͒, transmission electron microscopy ͑TEM͒, and secondary ion mass spectrometry ͑SIMS͒. An ultimate goal is to correlate the structural and compositional properties of the interface with the previously reported electrical characteristics.The Al 2 O 3 layers have been grown by ALCVD on Sifaced, n-type 4H-SiC samples with a 10 m thick epilayer ͑net doping level of 2 ϫ 10 15 cm −3 ͒ on a highly doped substrate ͑net doping level of 1 ϫ 10 18 cm −3 ͒, oriented 8°off the ͑0001͒ direction, purchased from Cree, Inc. Details of the cleaning and growth procedure can be found elsewhere. 4,5 For the AR-XPS measurements, 5 and 8 nm thick Al 2 O 3 layers were grown while thicker layers ͑ϳ110-120 nm͒ were deposited for the TEM and SIMS measurements. Annealing treatm...

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Aluminum oxide (Al2O3) has been grown by atomic layer deposition on n-type 4H-SiC with and without a thin silicon dioxide (SiO2) intermediate layer. By means of Capacitance Voltage and Thermal Dielectric Relaxation Current measurements, the interface properties have been investigated. Whereas for the samples with an interfacial SiO2 layer the highest near-interface trap density is found at 0.3 eV below the conduction band edge, Ec, the samples with only the Al2O3 dielectric exhibit a nearly trap free region close to Ec. For the Al2O3/SiC interface, the highest trap density appears between 0.4 to 0.6 eV below Ec. The results indicate the possibility for SiC-based MOSFETs with Al2O3 as the gate dielectric layer in future high performance devices.