S. Majumdar

Temperature dependent electrical transport in p-ZnO/n-Si heterojunction formed by pulsed laser deposition

ZnO film, with urea as nitrogen source to dope its p-type, is deposited by pulsed laser on n-type (100) Si substrate to fabricate p-ZnO/n-Si heterojunctions. The current-voltage (I-V) characteristics of the heterojunction have been studied in the temperature range 140–300 K. The turn on voltage decreased with increasing temperature while the breakdown voltage is increased slightly. The forward current is greatly increased with increasing temperature, while the reverse current is increased nominally. Both the decrease in barrier height and the increase in ideality factor with decrease in temperature are indicative of deviation from the pure thermionic emission-diffusion mechanism. The ln(I0) versus 1/kT plot exhibits the linear portion corresponding to an activation energy of 0.07 eV. Temperature-dependent forward current measurements suggest that trap-assisted multistep tunneling is the dominant carrier transport mechanism in this heterojunction. C-V analysis indicates an abrupt interface and band bending...

Effect of Al concentration in grain and grain boundary region of Al-doped ZnO films: a dielectric approach

Aluminium-doped zinc oxide (ZnO : Al) films have been deposited by RF magnetron sputtering on Pyrex glass substrates. The structural, electrical and optical properties of films as a function of Al concentration have been studied. Al-doped films exhibit high optical transparency and a reduction of resistivity with increasing Al concentration. The minimum resistivity value is found to be ρ = 2.2 × 10−3 Ω cm as compared with ~104 Ω cm, for undoped ZnO. The optical band gap is observed to follow a Burstein–Moss shift with the increase in the concentration of Al doping and shows the maximum band gap of 3.53 eV. Relative variation of the grain and grain boundary scattering with doping concentration has been investigated with impedance spectroscopy.

Evolution of strain and composition of Ge islands on Si (001) grown by molecular beam epitaxy during postgrowth annealing

Self-assembled Ge islands have been grown using a Stranski–Krastanov growth mechanism on Si (001) substrates by solid source molecular beam epitaxy. We performed time varying annealing experiments at a representative temperature of 650 ° C to study the shape and size evolution of islands for a relatively high Ge coverage. Islands are found to coarsen due to heat treatment via structural and compositional changes through continuous strain relaxation. Different island morphologies, namely, “pyramids,” “transitional domes,” and “domes” are found during the annealing sequence. The dominant coarsening mechanisms for the temporal evolution of islands of as-grown and annealed samples are explained by the comprehensive analysis of Rutherford back scattering, Raman spectroscopy, high-resolution x-ray diffraction, and atomic force microscopy. A correlation of the morphological evolution with the composition and strain relaxation of grown islands is presented.

Magnetic semiconducting diode of p-Ge1−xMnx/n-Ge layers on silicon substrate

We have synthesized Ge-based magnetic diode composed of a Mn-doped Ge film grown on lightly As-doped Ge on silicon substrate. p-Ge1−xMnx/n-Ge heterostructure behaves like a conventional diode under forward and reverse biases and works like a spin valve below Curie temperature (∼50 K) under zero (B=0) and nonzero (B=300 mT) magnetic fields at forward bias (+2 V). A hysteretic behavior of p-n junction current with small coercive magnetic field implies the nonvolatility of the diode. Thus, a single element of p-Ge1−xMnx/n-Ge on silicon substrate deserves nonvolatility, rectification, and spin-valve-like functionality.

Hopping conduction in nitrogen doped ZnO in the temperature range 10–300 K

Electrical transport mechanism in as-prepared and nitrogen (N) doped zinc oxide (ZnO) thin films has been investigated in the temperature range 10–300 K. The samples were grown by pulsed laser deposition in oxygen (O) ambience. The doped films show p-type conductivity at room temperature. It is found that there exist three distinct temperature regimes of the conduction in both as-prepared and N-doped ZnO in the said temperature range, viz., in the temperature range 10–50 K, variable range hopping is the dominant conduction mechanism whereas in the regime 50–210 K, the conduction is dominated by thermally activated hopping, whereas above 230 K, the transport is governed by the thermally activated carriers. However, a stable phase with no change in conductivity is observed in temperature range 210–230 K for N-doped ZnO. N-induced defects in ZnO lattice behave as localized hopping center, which does not have enough activation energy for conduction in this temperature regime.

Realization of biferroic properties in La0.6Sr0.4MnO3∕0.7Pb(Mg1∕3Nb2∕3)O3–0.3(PbTiO3) epitaxial superlattices

A set of symmetric and asymmetric superlattices with ferromagnetic

Synthesis and temperature dependent photoluminescence properties of Mn doped Ge nanowires

La_{0.6}Sr_{0.4}MnO_3

Investigation of strain in self-assembled multilayer InAs/GaAs quantum dot heterostructures

(LSMO) and ferroelectric

Electrical characterization of p-ZnO/p-Si heterojunction

0.7Pb(Mg_{1/3}Nb_{2/3})O_3–0.3(PbTiO_3)

Effect of Li incorporation on the structural and optical properties of ZnO

as the constituting layers was fabricated on