We have investigated the structural and band alignment properties of nanoscale titanium dioxide (TiO 2) thin films deposited on epitaxial crystallographic oriented Ge layers grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy. The TiO 2 thin films deposited at low temperature by physical vapor deposition were found to be amorphous in nature, and high-resolution transmission electron microscopy confirmed a sharp heterointerface between the TiO 2 thin film and the epitaxially grown Ge with no traceable interfacial layer. A comprehensive assessment on the effect of substrate orientation on the band alignment at the TiO 2 /Ge heterointerface is presented by utilizing x-ray photoelectron spectroscopy and spectroscopic ellipsometry. A band-gap of 3.33 6 0.02 eV was determined for the amorphous TiO 2 thin film from the Tauc plot. Irrespective of the crystallographic orientation of the epitaxial Ge layer, a sufficient valence band-offset of greater than 2 eV was obtained at the TiO 2 /Ge heterointerface while the corresponding conduction band-offsets for the aforementioned TiO 2 /Ge system were found to be smaller than 1 eV. A comparative assessment on the effect of Ge substrate orientation revealed a valence band-offset relation of DE V (100) > DE V (111) > DE V (110) and a conduction band-offset relation of DE C (110) > DE C (111) > DE C (100). These band-offset parameters are of critical importance and will provide key insight for the design and performance analysis of TiO 2 for potential high-j dielectric integration and for future metal-insulator-semiconductor contact applications with next generation of Ge based metal-oxide field-effect transistors. V C 2014 AIP Publishing LLC.

The memory characteristics of atomic-layer-deposited high-HfAlO nanocrystals in a p-Si/SiO 2 /͓HfO 2 /Al 2 O 3 ͔/Al 2 O 3 /platinum structure have been investigated. After the annealing treatment, the high-HfAlO nanocrystals with a small diameter of Ͻ10 nm and high density of Ͼ5 ϫ 10 11 cm 2 have been observed by high-resolution transmission electron microscopy. A large hysteresis memory window of ϳ10.4 V has been obtained. The high-HfAlO nanocrystal memory capacitor with a small capacitance equivalent thickness of ϳ8.5 ± 0.5 nm shows a small leakage current density of ϳ22 A cm 2 at a gate voltage of −16 V. A large memory window of ϳ8 V has also been observed after 10 5 s of retention, due to the charge confinement in the high-HfAlO multilayer nanocrystals.Nanocrystal-based floating gate memory devices have recently attracted much attention due to their potential in the semiconductor industry to overcome the limitations of the polycrystalline-siliconoxide-͓silicon-nitride͔-oxide-silicon ͑SONOS͒ memory. 1,2 To enhance the performance of memory devices, it is important to keep the charge tightly trapped to avoid the charge loss problem of the SONOS memory devices. The high-charge-trapping layers have been reported by several research groups for nonvolatile memory device applications. 3-6 A lot of work has also been reported on nanocrystal floating gate memory devices with different materials, such as Si, 7-9 Ge, 10 SiGe, 11 high-, 12,13 and metal 14-20 for the next generation of nanoscale nonvolatile memory device applications. It is a challenging issue to obtain highly reproducible memory devices with a large memory window, high spatial density, and small size with narrow size distribution of the nanocrystals. We want to solve this common problem using high-nanocrystals formed by atomic layer deposition ͑ALD͒, which has not yet been reported. In this paper, nanoscale memory capacitors with high-HfAlO nanocrystals formed by ALD have been investigated. A large memory window of ⌬V Ϸ 10.4 V, small size of Ͻ10 nm, and high reproducibility of the high-HfAlO nanocrystals have been observed in a p-Si/SiO 2 /͓HfO 2 /Al 2 O 3 ͔/Al 2 O 3 /platinum structure for nanoscale high-performance flash memory device applications. A pure Al 2 O 3 charge-trapping memory device has also been fabricated for comparison.p-Type Si͑100͒ wafers with a resistivity of 15-25 ⍀ cm were cleaned by the RCA process. After cleaning the Si wafers, a tunneling oxide ͑SiO 2 ͒ with a thickness of 3 nm was grown by the rapid thermal oxide system at a substrate temperature of 1000°C for 20 s. Then, the high-HfO 2 ͑ϳ1.2 nm͒/Al 2 O 3 ͑ϳ0.8 nm͒ nanolaminate layers with five periods were grown by ALD. Then, a blocking oxide ͑high-Al 2 O 3 ͒ with a thickness of ϳ10 nm was deposited by ALD. A pure Al 2 O 3 film with a thickness of ϳ20 nm was also deposited on SiO 2 ͑3 nm͒/p-Si substrate by ALD for comparison. The precursor temperatures were 185°C for hafnium tetrachloride ͑HfCl 4 ͒ and 23°C for trimethylaluminium ͓Al͑CH 3 ͒ 3 ͔. The oxidant gas for the Hf and Al...

No abstract