Microstructure and phonon behavior in W/Si periodic multilayer structures

The crystallinity of the tungsten (W) phase was improved with an increase in the thickness of this layer in the periodic W/Si multilayer structure. Both the α- and β- W phases were grown simultaneously and the contribution of these phases has modified upon a change in the thickness of the W layers. For thinner W layers, the thermodynamically metastable β- W phase was dominated, and with an increase in thickness, this phase has suppressed, and the stable α- W phase became prominent. The crystallite size of these phases was almost linearly proportional to the thickness of the W layers in the multilayers. With the increase in thickness of Si layers in multilayers, Raman scattering showed a decrease in bond-angle deviation of Si-Si bonding in the amorphous Si phase. The study revealed, ordering of Si-Si bonding in the amorphous phase of Si with an increase in thickness of these layers in periodic W/Si multilayers.

SiSn mediated formation of polycrystalline SiGeSn

Si1-xSnx and Si1-x-yGexSny polycrystalline thin layers were grown using Sn nanodots as crystal nuclei. Si1-xSnx crystallization occurred around Sn nanodots, and the substitutional Sn content was estimated as high as 1.5%. In the case of the poly-Si1-x-yGexSny, Ge and Si were deposited simultaneously on the Sn nanodots, however, Ge was preferentially incorporated into the Sn nanodots, resulting in the formation of the poly-Si1-x-yGexSny with amorphous Si residue. It was found that the poly-Si1-xSnx formed by the Sn nanodots mediated formation can be used as the new virtual substrate to be alloyed with Ge, namely the 2step formation process consisting of poly-Si1-xSnx crystallization and Ge alloying with the Si1-xSnx is the effective formation process for the poly-Si1-x-yGexSny formation. This non-equilibrium process with achieving crystallization resulted in the substitutional Si and Sn content in the as-grown poly-Si1-x-yGexSny as high as 19.4% and 3.4%, respectively.

Noise Improvement of a-Si Microbolometers by the Post-Metal Annealing Process

To realize high-resolution thermal images with high quality, it is essential to improve the noise characteristics of the widely adopted uncooled microbolometers. In this work, we applied the post-metal annealing (PMA) process under the condition of deuterium forming gas, at 10 atm and 300 °C for 30 min, to reduce the noise level of amorphous-Si microbolometers. Here, the DC and temperature coefficient of resistance (TCR) measurements of the devices as well as 1/f noise analysis were performed before and after the PMA treatment, while changing the width of the resistance layer of the microbolometers with 35 μm or 12 μm pixel. As a result, the microbolometers treated by the PMA process show the decrease in resistance by about 60% and the increase in TCR value up to 48.2% at 10 Hz, as compared to the reference device. Moreover, it is observed that the noise characteristics are improved in inverse proportion to the width of the resistance layer. This improvement is attributed to the cured poly-silicon grain boundary through the hydrogen passivation by heat and deuterium atoms applied during the PMA, which leads to the uniform current path inside the pixel.

Maximum Achievable N Content in Atom-by-Atom Growth of Amorphous Si-B-C-N Materials

Amorphous Si-B-C-N alloys can combine exceptional oxidation resistance up to 1500 °C with high-temperature stability of superior functional properties. Because some of these characteristics require as high N content as possible, the maximum achievable N content in amorphous Si-B-C-N is examined by combining extensive ab initio molecular dynamics simulations with experimental data. The N content is limited by the formation of unbonded N2 molecules, which depends on the composition (most intensive in C rich materials, medium in B rich materials, least intensive in Si-rich materials) and on the density (increasing N2 formation with decreasing packing factor when the latter is below 0.28, at a higher slope of this increase at lower B content). The maximum content of N bonded in amorphous Si-B-C-N networks of lowest-energy densities is in the range from 34% to 57% (materials which can be grown without unbonded N2) or at most from 42% to 57% (at a cost of affecting materials characteristics by unbonded N2). The results are important for understanding the experimentally reported nitrogen contents, design of stable amorphous nitrides with optimized properties and pathways for their preparation, and identification of what is or is not possible to achieve in this field.