Kankat Ghosh

Epitaxial Gd2O3 on strained Si1−xGex layers for next generation complementary metal oxide semiconductor device application

Strained Si1−xGex (x = 0.1–0.4) layers were grown on Si(111) and Si(001) substrates using molecular beam epitaxy followed by the growth of epitaxial Gd2O3 thin films on Si1−xGex layers using same technique. Pt/Gd2O3/Si1−xGex/Si stacks fabricated by several in situ process steps exhibit excellent electrical properties. Surface and microstructural analysis of both Si1−xGex and Gd2O3 layers carried out by different in situ and ex situ tools reveal a relaxed epi-Gd2O3 layer on a strained Si1−xGex layer on both Si(111) and Si(001) substrates with sharp interfaces between the oxide and the SiGe layer. Standard electrical measurements, such as capacitance-voltage and leakage current analysis, demonstrate promising electrical properties for such metal oxide semiconductor capacitors. A capacitance equivalent thickness as low as 1.20 nm with associated leakage current density of 2.0 mA/cm2 was obtained for devices with 4.5 nm thin oxide films where the density of interface trap (Dit) was only ∼1011 cm−2 eV−1.

Superconductivity in epitaxial InN thin films with large critical fields

We report superconductivity in Chemical Vapor Deposition (CVD) and Plasma-Assisted Molecular Beam Epitaxy (PA-MBE) grown epitaxial InN films having carrier density ∼ 1019 − 1020cm-3. The superconducting phase transition starts at temperatures around Tc,onset∼3 K and the resistance goes to zero completely at Tc0 ∼ 1.6 K. The temperature dependence of the critical field HC2(T) does not obey a two fluid Casimir-Gorter (C-G) model rather it is well explained by the 2-D Tinkham model. The extrapolated value of the zero-temperature perpendicular critical field HC2(0) is found to be between 0.25 − 0.9 T, which is ten times greater than that of Indium metal. It may indicate the intrinsic nature of superconductivity in InN films. The angle dependence of critical field is well described by Lawrence-Doniach (L-D) model, which suggest the existence of quasi-2D superconducting layers.We report superconductivity in Chemical Vapor Deposition (CVD) and Plasma-Assisted Molecular Beam Epitaxy (PA-MBE) grown epitaxial InN films having carrier density ∼ 1019 − 1020cm-3. The superconducting phase transition starts at temperatures around Tc,onset∼3 K and the resistance goes to zero completely at Tc0 ∼ 1.6 K. The temperature dependence of the critical field HC2(T) does not obey a two fluid Casimir-Gorter (C-G) model rather it is well explained by the 2-D Tinkham model. The extrapolated value of the zero-temperature perpendicular critical field HC2(0) is found to be between 0.25 − 0.9 T, which is ten times greater than that of Indium metal. It may indicate the intrinsic nature of superconductivity in InN films. The angle dependence of critical field is well described by Lawrence-Doniach (L-D) model, which suggest the existence of quasi-2D superconducting layers.

Impact of GaN buffer layer thickness on structural and optical properties of AlGaN/GaN based high electron mobility transistor structure grown on Si(111) substrate by plasma assisted molecular beam epitaxy technique

AlGaN/GaN based double heterosturcture high electron mobility transistor (HEMT) structures were grown on GaN buffer/Si(111) substrate by plasma assisted molecular beam epitaxy (PAMBE) technique. The thickness of GaN buffer layer was varied to find out the optimum GaN buffer layer for a crack free heterostructure, exhibiting appreciable structural and optical results. Full width at half maximum (FWHM) of GaN (0002) x-ray diffraction (XRD) peak and that of top AlGaN layer was estimated to be as low as 576 arcsec and 396 arcsec respectively. Near band edge photoluminescence (PL) peak for GaN also showed a FWHM of only 21 meV. These studies show that AlGaN/GaN heterostructures epitaxially grown on Si(111) substrate with suitable GaN buffer layer using PAMBE technique are promising for HEMT application.