E.K. Evangelou

Electrical and structural characteristics of yttrium oxide films deposited by rf-magnetron sputtering on n-Si

Yttrium oxide dielectric films were grown by rf-magnetron sputtering on n-Si(100) substrates and annealed in vacuum at temperatures ranging from 400 to 600u200a°C. The main aim of this work was the investigation of the interface between the dielectric film and silicon. Both structural (x-ray diffraction and transmission electron microscopy) and electrical characterization were used for this purpose. No structural change was observed on the interfacial native oxide layer after annealing at 600u200a°C for 1 h. Metal–oxide–semiconductor structures defined by the evaporation of Al electrodes show low leakage currents, moderate dielectric constant (around 14), and high densities of positive charges trapped in the oxide. Hysteresis effects in capacitance–voltage (C–V) curves reduce with the annealing temperature. Another interesting observation is the parallel shift of the C–V curves along the voltage axis with frequency. An insulator trap model is proposed to explain this behavior.

Electrical characterization of the SiON/Si interface for applications on optical and MOS devices

An investigation of the electrical properties of the SiON/n-Si interface is presented for applications in MOS and/or optical devices. The SiON films were deposited onto n-type Si substrates by CVD using different [O]/[N] ratios. Subsequent metallization led to the creation of metal-oxide-semiconductor (MOS) devices and electrical characterization took place in order to identify their electrical properties. Electrical measurements included current–voltage, capacitance–conductance–voltage (C–G–V) measurements and admittance spectroscopy, allowing the determination of the interface state density, the traps time constant and their distribution. Post-deposition annealing was also used and the annealed samples were subjected to the same investigation. The interface state density was found to lie between 1.74 × 1012 eV−1 cm2 and 1.72 × 1011 eV−1 cm−2 and the post-deposition annealing reduced these values.

Dielectric properties of CVD grown SiON thin films on Si for MOS microelectronic devices

The bulk properties of SiON films grown on n-Si substrates by CVD are examined by means of electrical measurements and Rutherford backscattering spectroscopy (RBS). The main aim of this project was to investigate the performance of the films in order to test their suitability for the construction of CMOS devices with SiON being the gate insulator. The CVD technique was used to produce the films and subsequent metallization leads to the creation of MOS devices. Rutherford backscattering spectroscopy (RBS) was used to verify the film bulk properties. Electrical measurements including current–voltage, capacitance–conductance–voltage (C–G–V) measurements and admittance spectroscopy were performed allowing determination of the bulk trapped charges and the dielectric constant of the films. These charges were calculated to have values between 0.76 nCb and 2.54 nCb, while the dielectric constant of the films was found to be quite high, with values greater than 5 and as high as 34. The RBS concluded that the films were uniform, and the nitrogen concentration was not higher than 10%.

Absolute efficiency of rare earth oxysulphide screens in reflection mode observation

The absolute efficiency of X-ray phosphor screens was studied in reflection mode observation for two phosphor materials widely used in X-ray applications, namely Y2O2S:Tb and Gd2O2S:Tb. The efficiency proved to depend on the tube voltage and on the screen thickness. Comparisons are given between the efficiency of the same screens in reflection and transmission mode observation. Theoretical calculations based on a uniform screen model give results that are in very good agreement with the experimental data.

Post deposition annealing studies of lanthanum aluminate and ceria high-k dielectrics on germanium.

Abstract Germanium MOS transistors with high- k gates are good alternatives for the replacement of SiO 2 in order to improve the performance of modern devices. Especially rare-earth oxides on germanium deposited by molecular beam deposition (MBD) have shown improved electrical properties compared to previous used HfO 2 with a germanium oxynitride (GeON) interfacial layer. In this work we report on the influence of ex situ post-annealing treatment with forming gas on the electrical characteristics of LaAlO 3 /Al 2 O 3 /nGe and CeO 2 /nGe MIS capacitors. We have observed an improvement of the electrical characteristics after forming gas anneal (FGA) for LaAlO 3 /Al 2 O 3 /nGe in contrast to CeO 2 /nGe which shows no clear trend regarding the influence of FGA.

Device characterization for amorphous diamond-like carbon–silicon heterojunctions

We report here on the electrical characterization of Al/a-C:H/n-Si devices, where the a-C:H films were ion implanted with boron. The current–voltage characteristics versus temperature demonstrated the creation of p-n heterojunctions and Schottky diodes. Maximum current outputs were reached faster for higher temperatures. Lower doses of boron implants produced Schottky diode characteristics, with a current saturation in the forward region due to the existing barrier. The values of the output currents increased with temperature and implanted dose.

Electrical behaviour of metal/a-C/Si and metal/CN/Si devices

Abstract Electrical characterisation of metal/carbon/Si devices was performed. Amorphous carbon films rich in sp3 bonds were grown onto n-type Si substrates by RF magnetron sputtering at room temperature. Different deposition conditions were used to create different sp3 and sp2 configurations in order to examine their influence on the performance of electronic devices. Suitable metalisation was used to fabricate devices, which were then characterised electrically. Electrical characterisation using I–V, C–G–V and G–ω techniques showed temperature dependent currents through the devices which increase rapidly when forward bias is applied. This behaviour was found to be dependent on the sp3–sp2 contents of the films. The devices behaved like metal–insulator–semiconductor diodes with a defect insulator resulting in creating thermally activated currents through the devices. The effect of nitrogen introduced in the growth process to produce carbon nitride films was also examined. Different amounts of nitrogen were used and the same characterisation process has been used for a variety of samples. The films were nearly perfect insulators and the corresponding devices showed a clear MIS behaviour. Thus, the room temperature magnetron sputtering technique produced films, with electronic properties dependent on the C–C bonding configuration. Moreover it is shown that the nitrogenated films made under certain conditions can be used as insulators in devices.

EFFECT OF THE LAYERED STRUCTURE ON THE ELECTRONIC PROPERTIES OF AMORPHOUS CARBON FILMS ON N-SI

Amorphous carbon (a-C) films rich in sp3 bonds were grown onto n-type (100) silicon substrates by rf magnetron sputtering. The electrical defects created in the bulk of the carbon films as well as those at the a-C/Si interface during the deposition of the films were characterized electrically. Devices having the metal–insulator–semiconductor structure were fabricated and investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) profiling and admittance spectroscopy. The construction of the films and in particular the presence of layered and bilayer structures was shown to affect the device characteristics. This behavior was attributed to Ar+ ions trapped inside the carbon bulk as well as to charge deficiencies due to the specific growth conditions of the amorphous carbon layers. The density of the interface states was found to depend considerably on the film construction, ranging from 1011 to 1013u2002eV−1u2009cm−2. The dynamic behavior of the states was expressed by the relevant time constant,...

The effects of interface and bulk defects on the electrical performance of amorphous carbon/silicon heterojunctions

Abstract Amorphous diamond-like carbon (DLC)–silicon heterojunctions developed by rf magnetron sputtering from a carbon target on n-type Si(100) substrates at room temperature (RT) with TiN as a metal contact showed a high rectification ratio and asymmetric p–n junction characteristics. Classical current–voltage (I–V) measurements at various temperatures allowed to derive the conduction mechanisms which are directly related to the number of defects in the bulk of the material or at the interface between the Si and the amorphous carbon. Low frequency noise measurements at RT provided the concentration of states or traps that create the fluctuation of the current through the device and was used to clarify their role as far as the electrical properties of the material are concerned. Low temperature admittance spectroscopy was also used to measure the density of interface traps and the results were found to agree with those of the noise measurements. In particular, the density of states was found to be of the order of 1012 eV−1xa0cm−2 and their time constant of the order of 10−4 s. All of the above were suitably used and used in order to explain the defects contribution on the conduction mechanisms and the device behaviour.

Avalanche-induced excess noise in polycrystalline silicon thin-film transistors

The low-frequency noise behavior of polycrystalline silicon thin-film transistors, operated in the avalanche multiplication region of the output characteristics, is investigated. The avalanche-induced current noise, originating from generation-recombination processes in the depletion region of the drain junction, can be described by the carrier number fluctuation model. Using a model for the excess noise in silicon-on-insulator metal-oxide-semiconductor field-effect transistors operated in the kink regime, an analytical expression for the avalanche-induced current noise is derived taking into account an exponential distribution of the gap states. Comparison of the experimental noise data with the theoretical model indicates that, in addition to the avalanche multiplication, hot-carrier effects contribute significantly to the current increase in the avalanche regime.