M. Senthil Kumar

Investigations on Al/BaTiO3/GaN MFS structures

Abstract A metal–insulator–semiconductor (MIS) device structure has been established on GaN by using BaTiO 3 , a ferroelectric material, as an insulating layer. The composition of the deposited ferroelectric layers was studied using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) analysis. Fabricated Al/BaTiO 3 /GaN metal–ferroelectric–semiconductor (MFS) structures have been characterised through capacitance–voltage ( C – V ) measurements. Improved C – V characteristics have been observed in comparison to other traditional oxide insulators. An inversion of GaN MFS structures has been attained just for the applied voltage of 5 V due to the high dielectric constant and large polarisation field of the gate ferroelectric layer. The bias stress measurements indicate a high stability of the ferroelectric material over a period of 10 4 s.

Electrical and optical isolation of GaN by high energy ion irradiation

Unintentionally doped n-type gallium nitride (GaN) epitaxial layers grown by MOCVD technique on sapphire substrates have been subjected to 70 MeV nitrogen ion irradiation for various fluences. The sheet resistivity of GaN layer increases by 7 orders of magnitude for high fluence irradiation while its mobility and carrier concentration decrease as a function of ion fluence. The increase in sheet resistivity of GaN layer is explained with grain boundary controlled transport mechanism and the mobility degradation due to radiation induced charged scattering centers. Using deep level transient spectroscopy technique, a new deep level trap at 0.135 eV below the conduction band has been identified as a result of nitrogen ion irradiation. The photoluminescence emission of GaN layer decreases with increase in ion fluence and is completely quenched for high fluence irradiation.

Investigations on the CdS passivated anodic oxide–InP interface for MOS structures

Abstract Thin layers of cadmium sulfide have been deposited on 〈111〉 n-InP using the chemical bath deposition technique at room temperature. X-ray photoelectron spectroscopy (XPS) results show that sulfur in CdS removes native oxide present on the InP surface and forms a chemically stable surface. Anodic oxidation was carried out on the CdS passivated InP surface. XPS results of oxides show the formation of highly stable P2O5. Improved C–V characteristics have been observed on CdS treated MOS diodes. Delay time measurements and bias stress measurements demonstrate the high stability of CdS passivated MOS diodes. NSS values as low as 3×1010 cm−2 eV−1 were obtained for CdS treated MOS diodes.

Raman scattering studies on hydrogen ion-implanted GaN

Abstract The metal organic chemical vapour deposition (MOCVD) grown unintentionally doped n-type GaN epitaxial layers on sapphire substrates have been implanted with H+ for various doses from 1014 to 10 16 cm −2 with multiple energies ranging from 40 to 120 keV. Raman spectra have been recorded on as-grown, H+-implanted GaN samples and on virgin sapphire substrate. E2 (high) and A1(LO) Raman modes of GaN layer have been observed and analysed. The behaviour of Raman shift, FWHM and area of GaN modes with H+ dose are explained on the basis of hydrogen substituting nitrogen atom, implantation-induced lattice damage and light attenuation by lattice damage in GaN layer.

Deep Level Transient Spectroscopic Analysis on Au/SiO2/InP MOS Structures

Deep Level Transient Spectroscopy (DLTS) studies have been carried out on Au/SiO 2 /InP Metal-Oxide-Semiconductor (MOS) diodes. Majority and minority carrier traps have been observed for the room temperature SiO 2 deposited samples, The effect of substrate temperature during SiO 2 deposition has been analysed using DLTS. It has been observed that the minority carrier trap is removed while SiO 2 deposition is carried out at an elevated temperature. The detected traps have been analysed under different reverse bias values to distinguish between the bulk and interface traps.

Growth and characterizations of various GaN nanostructures on C-plane sapphire using laser MBE

We have grown various GaN nanostructures such as three-dimensional islands, nanowalls and nanocolumns on c-plane sapphire substrates using laser assisted molecular beam epitaxy (LMBE) system. The shape of the GaN nanostructures was controlled by using different nucleation surfaces such as bare and nitridated sapphire with GaN or AlN buffer layers. The structural and surface morphological properties of grown GaN nanostructures were characterized by ex-situ high resolution x-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. The symmetric x-ray rocking curve along GaN (0002) plane shows that the GaN grown on pre-nitridated sapphire with GaN or AlN buffer layer possesses good crystalline quality compared to sapphire without nitridation. The Raman spectroscopy measurements revealed the wurtzite phase for all the GaN nanostructures grown on c-sapphire.

Low temperature laser molecular beam epitaxy and characterization of AlGaN epitaxial layers

We have grown AlGaN (0001) epitaxial layers on sapphire (0001) by using laser molecular beam epitaxy (LMBE) technique. The growth was carried out using laser ablation of AlxGa1-x liquid metal alloy under r.f. nitrogen plasma ambient. Before epilayer growth, the sapphire nitradation was performed at 700 °C using r.f nitrogen plasma followed by AlGaN layer growth. The in-situ reflection high energy electron diffraction (RHEED) was employed to monitor the substrate nitridation and AlGaN epitaxial growth. High resolution x-ray diffraction showed wurtzite hexagonal growth of AlGaN layer along c-axis. An absorption bandgap of 3.97 eV is obtained for the grown AlGaN layer indicating an Al composition of more than 20 %. Using ellipsometry, a refractive index (n) value of about 2.19 is obtained in the visible region.

Crystal and molecular structure of 3-benzoylpropionic acid

C10H10O3, monoclinic,P21/c,a=15·071(10),b=5·435(9),c=16·058(10) Å, β=129·57 (10)o,V=1013·7Å3,Z=4,Dm=1·17 gm/cm3,Dc=1·16 gm/cm3, λ (CuKα)=1·5418Å, μ=6·8 cm−1,Mr=178·2. The structure was refined toR=0·10 for 637 observed reflections. The intensity data were estimated visually by the equi-inclination multiple film Weissenberg technique withb as the rotation axis using Ni-filtered CuKα radiation. The interplanar angle between the carboxyl group and the benzene ring is 81(1)o. The molecules are linked in dimers around a centre of symmetry by O−H…O hydrogen bonds (2·76Å).