Roland L. Van Meirhaeghe

Atomic layer deposition of TiO2 from tetrakis-dimethyl-amido titanium or Ti isopropoxide precursors and H2O

Atomic layer deposition (ALD) of TiO2 thin films using Ti isopropoxide and tetrakis-dimethyl-amido titanium (TDMAT) as two kinds of Ti precursors and water as another reactant was investigated. TiO2 films with high purity can be grown in a self-limited ALD growth mode by using either Ti isopropoxide or TDMAT as Ti precursors. Different growth behaviors as a function of deposition temperature were observed. A typical growth rate curve-increased growth rate per cycle (GPC) with increasing temperatures was observed for the TiO2 film deposited by Ti isopropoxide and H2O, while surprisingly high GPC was observed at low temperatures for the TiO2 film deposited by TDMAT and H2O. An energetic model was proposed to explain the different growth behaviors with different precursors. Density functional theory (DFT) calculation was made. The GPC in the low temperature region is determined by the reaction energy barrier. From the experimental results and DFT calculation, we found that the intermediate product stability ...

Growth Kinetics and Crystallization Behavior of TiO2 Films Prepared by Plasma Enhanced Atomic Layer Deposition

cSCK-CEN, Boeretang 200, B-2400 Mol, Belgium Atomic layer deposition ALD of TiO2 films from tetrakisdimethylamido titanium TDMAT or titanium tetraisopropoxide TTIP precursors was investigated. The growth kinetics, chemical composition, and crystallization behavior of the TiO2 films were compared for combinations of the two precursors with three different sources of oxygen thermal ALD using H2O and plasma-enhanced ALD PEALD using H2 Oo r O 2 plasma. For TDMAT, the growth rate per cycle GPC decreased with increasing temperature; while for TTIP with either water plasma or O2 plasma, a relatively constant growth rate per cycle was observed as a function of substrate temperature. It was found that the crystallization temperature of the TiO2 films depends both on film thickness and on the deposition conditions. A correlation was observed between the TiO2 crystallization temperature and the C impurity concentration in the film. The TiO2 films grown using a H2O plasma exhibit the lowest crystallization temperature and have no detectable C impurities. In situ X-ray diffraction measurements were used to test the diffusion barrier properties of the TiO2 layers and proved that all TiO2 films grown using either H2 Oo r O2 plasma are dense and continuous.

Crystallographic and luminescent properties of orthorhombic BaAl2S4:Eu powder and thin films

BaAl2S4:Eu thin films were prepared from a multilayered BaS:Eu∕Al2S3 thin-film structure, deposited with electron-beam evaporation. Depending on the deposition and postdeposition annealing temperature, europium-doped BaAl2S4 thin films can show both an orthorhombic and the more common cubic crystal structure. The lattice constants of the orthorhombic BaAl2S4 are determined from powder-diffraction data. The photoluminescent properties of europium-doped orthorhombic and cubic BaAl2S4 powders are compared. The occurrence of both phases in thin films is discussed in terms of substrate and postdeposition annealing temperature. A temperature of 600°C is sufficient to obtain the orthorhombic phase, and annealing at 900°C leads to the cubic phase. The phase formation in the multilayered thin films is investigated by studying the crystallographic, optical, and photoluminescent properties.

Effect of Moisture on Performance of SrS:Ce Thin Film Electroluminescent Devices

Although the continuing research on blue thin film electroluminescence has led to fairly stable and efficient SrS:Ce devices, there is still a lack of fundamental knowledge about the origin of the remaining instability. The purity and stability of both the SrS host semiconductor and the Ce activator have been examined, in the starting materials as well as in the evaporated thin films. It is found that the SrS host is relatively inert, but that it is imperative to choose a moisture-insensitive Ce-based activator.

Electrochemical reduction vs. vapour deposition for n-GaAs/Cu Schottky-barrier formation: a comparative study

Copper has been deposited electrochemically upon (100) n-GaAs at different electrode potentials. The height of the Schottky barriers thus formed was measured and compared to that of n-GaAs/Cu junctions prepared by vapour deposition. Whereas, initially, the barrier height, ΦB, was about the same for both types of junctions, ΦB was seen to increase with time when the electrochemically formed barriers were left in air. The morphology of the copper phase was studied by atomic force microscopy (AFM), revealing a relationship between the roughness of the copper layer and the occurrence of the ageing effect. From these data, an interpretation for the latter was proposed, based upon the growth of an interfacial oxide layer.

Point-Defect Generation in Ni-, Pd-, and Pt-Germanided Schottky Barriers on N-Type Germanium Substrates

In this paper, the creation of point defects in n-type germanium by Ni-, Pd or Pt-germanidation is investigated by means of Deep Level Transient Spectroscopy (DLTS). The germanidation is achieved by a Rapid Thermal Annealing (RTA) step between 300 and 500oC of a 30 nm sputtered metal layer. Contrasting behaviour is found between Ni, on the one hand, and Pd and Pt, on the other: in-diffusion of nickel is found starting from 400oC, while in the second case, vacancy-related deep levels have been observed at the lower RTA temperatures. Evidence will be provided that these defects are most likely formed during the sputtering of the heavy metal atoms, introducing radiation damage in the Ge substrate. Finally, the impact of these deep levels on the current-voltage (I-V) characteristics of the obtained metal-germanide Schottky barriers will be discussed.