Kyu Hwan Shim

Structural properties of nickel silicided Si1−xGex(001) layers

We have investigated the interfacial reactions of Ni films on Si1−xGex (x = 0.0–0.2) epitaxial (001) layers as a function of the annealing temperature between 300 and 800 °C. It is shown that the Ni-silicided Si1−xGex layers have a higher sheet resistance and poorer surface and interface morphologies, compared to the Ni-silicided Si layer. As the annealing temperature is increased, the silicide layers become irregular with thermal grooving and, consequently, become agglomerated. This is more severe in the sample with a higher Ge content. Glancing angle x-ray diffraction results show that, unlike the Ni-silicided Si sample, for the Si1−xGex (x = 0.1 and 0.2) samples, no phase transition from Ni germanosilicide (Ni(Si1−mGem)) to Ni(Si1−nGen)2 occurs throughout the annealing temperature domain. Transmission electron microscopy and energy dispersive spectroscopy results show that Ge atoms outdiffuse from the Ni germanosilicide as the annealing temperature increases. The outdiffused Ge atoms are segregated at the Ni germanosilicide/Si1−xGex interfaces and at the surface regions between the agglomerated germanosilicide. A simple model is given to describe the Ge segregation and silicide islanding behaviours.

Improvement of the morphological stability of Ni-silicided Si0.8Ge0.2 layers by using a molybdenum interlayer

We have investigated the effect of a Mo interlayer on the structural and electrical properties of Ni-silicided Si0.8Ge0.2 samples. It is shown that the samples with the interlayers give lower sheet resistances than the samples without the interlayers when annealed at temperatures in the range of 450–800 °C. Glancing angle x-ray diffraction results show that regardless of the interlayers, only the Ni germanosilicide phase is formed across the whole temperature range. Scanning electron microscopy results show that the samples with the interlayers remain stable without serious surface degradation up to 600 °C. It is further shown that the samples without the interlayers experience abnormal oxidation at a fairly low temperature of 500 °C, while the interlayered samples remain stable without significant oxidation up to 800 °C. The Mo interlayer is found to move toward the surface region, when annealed at temperatures in excess of 450 °C. It is shown that the addition of the Mo interlayer effectively improves t...

Depth-Resolved Cathodoluminescence of III–V Nitride Films Grown by Plasma-Assisted Molecular Beam Epitaxy

The luminescence properties of III–V nitride films (an undoped GaN, an undoped GaN/Al0.2Ga0.8N multiquantum well, and a p-type Mg-doped GaN films) were investigated using the depth-resolved cathodoluminescence (CL) spectroscopy. From the low- and room-temperature CL of the undoped GaN and GaN/AlGaN MQW films, an emission at 2.9 eV was found with the longer penetration depth and is attributed to the higher density of dislocations at the interface between the film and the substrate. In order to explain the depth-resolved CL of the Mg-doped GaN film, the configuration coordinate model is proposed on the basis of the local strain near the Mg impurities. This model demonstrates that local strain may play a crucial role in controlling the radiative efficiency, line width, and peak position of the luminescence from the film.