| Photonic Materials Technology Section (PMTS) |
Photonic Materials Technology Section (PMTS)
Nano-Electronic Materials and Devices Laboratory
Other technologically important materials
LaB6 nanostrutures for field emission: LaB6 (Lanthanum hexaboride) films have been deposited on verity of substrates such as tungsten and Rhenium flats and pointed tips by pulsed laser deposition technique. The field emission studies on have been performed in the conventional field emission geometry. In case of LaB6/tungsten tip, the Fowler-Nordheim plot obtained from the current-voltage characteristic was found to be linear in accordance with the quantum mechanical tunneling phenomenon. A current density of 1.2×104 A/cm2 was drawn from the deposited tip. The field enhancement factor was calculated to be 5537cm−1, indicating that the field emission was from nanoscale protrusions present on emitter surface. The emission current-time plots showed very good stability of the emitter.
CMR materials: Epitaxial thin films of Colossal Magneto-resistance (CMR) material La0.5Pr0.2Ba0.3MnO3 were deposited on LaAlO3 single-crystal substrates using pulsed laser deposition (PLD) technique with different growth parameters. Structural, surface morphological, electrical, and magnetotransport measurements on these films revealed that unoptimized growth parameters during the deposition using the third harmonic of a Q-switched Nd: YAG laser yielded structurally inhomogeneous epitaxial films having a columnar morphology, while the optimized growth parameters using an excimer laser during the PLD resulted in homogeneous epitaxial films with a smooth morphology. Interestingly, at a temperature of 5 K, the films with unoptimized growth parameters showed a large high-field magnetoresistance (MR) of ~90% while the films with optimized growth parameters showed a high-field MR of only ~15%. It is contemplated that this exceptionally large MR in the un-optimized films might be due to the phase separation and coexistence of metallic and insulating phases.
Si Nanoparticles: We have grown particulate free multilayer structure of Al2O3 capped Si quantum dots of different mean sizes ranging from 1 nm to 3 nm as confirmed by TEM analysis by using a off-axis pulsed laser deposition scheme. A monotonic blueshift in the band-gap of Si nanoparticles with decreasing particle size as observed in photoabsorption spectra of Si nanoparticles was in line with the putative quantum confinement effects. Room temperature photoluminescence from Si quantum dots grown for different times showed features without any apparent size dependent spectral shift which, albeit has earlier been explained by others originating from the defect levels at the interface of Si and SiO2 shells surrounding the nanoparticles but still have certain mysteries attached.
Laser Induced Oxidation of Si surface to grow of ultra-thin SiO2: Downscaling of device dimensions is essential for the development of new generation ultra large scale integrated (ULSI) circuits based on complementary metal oxide semiconductor field effect transistors (CMOSFET). However, because of continuous downscaling, the thickness of SiO2 gate dielectric has already reduced to a few mono-layers. Further thinning of SiO2 poses several challenges, including control of growth and uniformity of ultra-thin SiO2. We have very recently reported a novel technique based on pulsed laser heating to grow ultra-thin SiO2 with thickness less than 4 nm on the surface of Si substrate kept at room temperature [329]. Third harmonic laser pulse of a Q-switched Nd:YAG laser (355 nm) with a repetition rate of 10 Hz and pulse width of 6 ns was used to heat the silicon wafer in O2 ambient pressure to grow SiO2 in a very controlled manner. The laser fluence on the substrate was maintained at ~ 75 mJ/cm2. SiO2 was grown for different durations in the range of 30 to 180 sec in an oxygen pressure of ~ 10-2 Torr. The leakage current density against applied gate voltage (J–V) characteristics of the MOS devices using controlled pulsed laser heating revealed the low leakage current density and the breakdown field strength >10 MV/cm, signifying the excellent quality of the laser induced oxide.
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