Papers by Author: Ola Nilsen

Abstract: ZnO/n-Si and ZnO/p-Si heterostructures were prepared by Atomic layer deposition (ALD) and the electronic properties have been investigated by Current-Voltage (I-V), Capacitance-Voltage (C-V) and Deep level transient spectroscopy (DLTS) measurements. DLTS measurements show two dominants electron traps at the interface of the ZnO/n-Si junction with energy position at 0.07 eV and 0.15 eV below the conduction band edge, labelled E(0.07) and E(0.15), respectively, and no electrically active defects at the interface of the ZnO/p-Si junction. E(0.07) is reduced by annealing up to 400°C while E(0.15) is created at 500°C. The best heterostructure is found after heat treatment at 400°C with a substantial improvement of the current rectification for ZnO/n-Si and the formation of Ohmic contact on ZnO/p-Si. A reduction of the interface defects correlates with an improvement of the crystal structure of the ZnO film with a preferred orientation along the c-axis.

Abstract: Using impedance spectroscopy (IS) for characterization of the electrical properties and gas sensing characteristics of Al2O3/4H-SiC (MOS) structures, insight on the capacitive and resistive contributions in the interfacial region of the MOS structures is obtained. Applying DC bias voltages between accumulation and depletion (corresponding to the interfacial region) allows investigation of the voltage shift of the capacitance versus voltage (CV) curve at different temperatures and atmospheres. This voltage shift forms the basis to use the MOS structure as a gas sensor. The MOS capacitance, as extracted from IS data, is different from the one obtained using CV measurements, due to the ability of distinguishing the resistive contribution (using IS). Voltage shifts between 1 and 2 V are clearly revealed during exposure to hydrogen and oxygen, and this shift exhibits a long-term stability of operation at temperatures up to 500°C. Hence, Al2O3 exhibits great promise as a gate dielectric in MOS-based gas detecting devices for use at elevated temperatures.

Abstract: Al2O3 grown by Atomic Layer Chemical Vapour Deposition (ALCVD) on n-type 4H-SiC with a nominal thickness of 100nm has been characterized by Grazing Incidence X-Ray Diffraction (GIXD) and Specular X-Ray Reflectivity (SXR) measurements. After post-deposition, the samples were annealed at different temperatures and durations in argon atmosphere. The GIXD results reveal crystallization at temperatures above 900°C, most likely in the form of θ-Al2O3 or γ-Al2O3. However, the formation of a new, non-stoichiometric Al2O3 phase cannot be excluded. The crystalline domain size, evaluated from the peak FWHMs after subtraction of the instrumental broadening, is found to be almost equal (18±1nm), independent of T in the range 900°C≤T≤1100°C and time in the range 1h≤t≤3h. From SXR, mass density profiles are derived. Whereas the as grown film exhibits the lowest mass density, at 800°C a low-density interface layer forms. At the same time, it appears that the initial crystallization starts at the surface. At 900°C, the density increases sharply (this process involves film crystallization) and the film thickness correspondingly reduces. Whereas the density increase and thickness reduction still continue for T>900°C (tendency to the density α-Al2O3), the density of the interfacial layer has a minimum at 900°C and gradually increases for higher temperatures. From Atomic Force Microscopy (AFM) investigations it could be revealed that the starting of the crystallization at 900°C is accompanied with a substantial surface roughening. For annealing at higher temperatures, the surface roughness is in the range of the one of the as-grown sample (about 6Å).

Abstract: Al2O3 has been grown by Atomic Layer Chemical Vapour Deposition (ALCVD) on ntype 4H-SiC using O3 as an oxidant and tri-methyl-aluminum (TMA) as a precursor. After deposition, annealing at 1000°C during 3h in different atmospheres (Ar, N2 and O2) was performed. Interface properties were studied by Capacitance-Voltage (CV) and Thermal Dielectric Relaxation Current (TDRC) measurements. The highest near-interface trap density (Nit) was deduced to be 4x1012 eV-1cm-2 between 0.36 eV and 0.5 eV below the conduction band, Ec, for O2 annealed samples, 2.8x1012 eV-1cm-2 between 0.42 eV and 0.56 eV below Ec for Ar annealed samples and 2.2x1012 eV-1cm-2 between 0.4 eV and 0.6 eV below Ec for N2 annealed samples. Only samples annealed in Ar exhibit a nearly trap free region close to Ec. Annealing in N2 is found to decrease Nit between 0.3 and 0.7 eV but shows a slightly higher Nit close the conduction band compared to the Ar case.

Abstract: Al2O3 has been grown by Atomic Layer Chemical Vapour Deposition (ALCVD) on ntype 4H-SiC using O3 as an oxidant. After post-deposition, annealing at high temperature (1000°C) in Argon atmosphere for different time periods (1h, 2h, 3h) was performed. Bulk and interface properties of the as-grown as well as the annealed films were studied by electrical measurements (CV, IV, DLTS) and Secondary Ion Mass Spectrometry (SIMS) measurements. The electrical measurements show a decreasing shift of the flatband voltage indicating a diminution of the negative oxide charges with increasing annealing time. After annealing at 1000°C for 3h, the flatband voltage shift has decreased to 6V. The SIMS measurements indicate a double interface with a SiOx (x ≤ 2) interlayer in the as-grown samples while only one interface is observed after annealing, leading to improved electrical behavior of the Metal-Oxide-Semiconductor devices.

Abstract: In this study, electrical properties of Al2O3 deposited by Atomic Layer Deposition (ALCVD) on n-type 4H-SiC were investigated. Metal-Oxide-Semiconductor (MOS) capacitors were characterized by various electrical techniques such as Capacitance-Voltage (CV), Current- Voltage (IV) and Deep Level Transient Spectroscopy (DLTS) measurements. Two different oxidants, H2O and O3, have been used for the oxide deposition. After deposition, the flat-band voltage shift is much less using O3 than H2O (~ 7V versus ~ 20V). Annealing treatment has been carried out at different temperatures in Ar atmosphere up to 700°C. Whereas the flat-band voltage shift can be reduced by annealing, the leakage current remains rather high.