Shojan P. Pavunny

Structural, electrical, and magnetic properties of chemical solution deposited BiFe1−xTixO3 and BiFe0.9Ti0.05Co0.05O3 thin films

BiFeO3 (BFO), BiFe1−xTixO3, and BiFe0.9Ti0.05Co0.05O3 thin films were deposited on Pt/TiO2/SiO2/Si substrates by chemical solution deposition. BFO film has distorted rhombohedral R3c structure and in BiFe1−xTixO3 (104)/(110) reflections broadened suggesting limited grain growth with Ti substitution. The surface roughness (rms) decreased in the case of Ti substituted BFO. Up to 5% Ti in the lattice reduces the leakage current substantially. For BiFe1−xTixO3, the leakage current qualitatively followed the same trend and the behavior resembles to space charge limited current conduction. The magnetic properties were completely lost by Ti substitution and slightly recovered upon cosubstitution with magnetically active Co. The disappearance of ferromagnetic hysteresis of BFO with Ti substitution and its reappearance with Co is suggestive of the origin of magnetic properties consequential from the BFO lattice itself and hence support it as an intrinsic property of BFO. Capacitance-voltage characteristics of BFO,...

Raman spectroscopy and field emission characterization of delafossite CuFeO2

Delafossite p-type CuFeO2 (CFO) semiconductors were synthesized by a modified solid state reaction technique and investigated by x-ray diffraction, x-ray photoemission spectroscopy (XPS), energy dispersive x-ray spectroscopy, and scanning electron microscopy, revealing the single-phase nature of CFO with 1:1 Cu/Fe atomic ratio. The valance states of CFO were examined by XPS and suggest Cu and Fe ions are in +1 and +3 valance states with high spin S=5/2. The “turn-on field” which is the macroscopic field needed to get an emission current of 9 nA, was calculated as 5.72 V/μm. Room temperature Raman spectra of CFO displayed two main Raman active modes at Eg∼351 cm−1 and Ag∼692 cm−1 in accord with other delafossite structures. Temperature dependent Raman spectra showed that both the modes shifted to lower frequency with significant decrease in intensity with increase in temperature. Frequency shift and linewidth of both phonon lines matched well with the theoretical damped harmonic oscillator model based on t...

Multilevel unipolar resistive memory switching in amorphous SmGdO3 thin film

Multilevel resistive switching was observed in random access memory device using amorphous SmGdO3 (SGO) ternary oxide thin films. Non-volatile and stable 4-level resistance states with sufficient margin of resistance ratios were observed by varying compliance current which was attributed to compliance current dependent variation in size of conducting filaments. As fabricated Pt/SGO/Pt devices exhibited excellent switching parameters such as stable resistance ratios of reset (ON) to set (OFF) states, non-overlapping switching voltages, excellent data retention, and endurance. Temperature dependent variation of resistances of ON and OFF states of the device was studied to elucidate current conduction and resistive switching mechanisms.

DyScO3 buffer layer for a performing metal-ferroelectric-insulator-semiconductor structure with multiferroic BiFeO3 thin film

Metal-ferroelectric-insulator-semiconductor structures with a BiFeO3 ferroelectric layer and DyScO3 insulating buffer layer were fabricated and characterized. BiFeO3 film was polycrystalline with rhombohedral structure and DyScO3 film was amorphous. The size of the capacitance-voltage memory window (ΔVFB) was investigated as a function of voltage sweep and frequency; ΔVFB increased to a saturation value of 1.7 V with the sweep voltage and it almost remained constant over a frequency range of 1 kHz to 1 MHz.

Dielectric anomalies due to grain boundary conduction in chemically substituted BiFeO3

We describe systematic studies on Nd and Mn co-doped BiFeO3, i.e., (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3 (BNFM) polycrystalline electroceramics. Raman spectra and X-ray diffraction patterns revealed the formation of rhombohedral crystal structure at room temperature, and ruled out structural changes in BiFeO3 (BFO) after low percentage chemical substitution. Strong dielectric dispersion and a sharp anomaly around 620 K observed near the Neel temperature ( TN ∼ 643 K of BFO) support strong magneto-dielectric coupling, verified by the exothermic peak in differential thermal data. Impedance spectroscopy disclosed the appearance of grain boundary contributions in the dielectric data in the region, and their disappearance just near the Neel temperature suggests magnetically active grain boundaries. The resistive grain boundary components of the BNFM are mainly responsible for magneto-dielectric coupling. Capacitive grain boundaries are not observed in the modulus spectra and the dielectric behavior deviates from the ...

Structural, electrical, and magnetic properties of chemical solution deposited Bi(Fe0.95Cr0.05)O3 thin films on platinized silicon substrates

Polycrystalline BiFeO3 and Bi(Fe0.95Cr0.05)O3 thin films were deposited on Pt/TiO2/SiO2/Si substrates by chemical solution deposition. Their structural, electrical, and magnetic properties were measured and compared. The prominent splitting around 2θ∼32° for the 104/110 reflections and the resemblance of Raman spectra with BiFeO3 suggests structural invariance upon Cr substitution (≤5%). The surface morphology of the films showed uniform granular grains; roughness and the grain sizes reduced considerably with Cr substitution. In the case of Bi(Fe0.95Cr0.05)O3 thin films, all Raman active modes disappeared at 700 °C suggesting a structural phase transition with the reduced transition temperature compared to pure BFO. The dielectric constant of pure BiFeO3 film is approximately 50 at 1 MHz and it increased to 66 with 5% Cr substitution. The leakage current reduced in Bi(Fe0.95Cr0.05)O3 thin films and the current conduction was due to Poole–Frenkel mechanism compared to the space charge limited current condu...

Photovoltaic properties of Aurivillius phase Bi5FeTi3O15 thin films grown by pulsed laser deposition

We report a remarkable photovoltaic effect in pulsed laser deposited multiferroic aurivillius phase Bi5FeTi3O15 (BFTO) thin films sandwiched between ZnO:Al transparent conductive oxide top electrode and SrRuO3 bottom electrode fabricated on amorphous fused silica substrates. The structural and micro structural properties of these films were analysed by X-ray diffraction and atomic force microscopy techniques. The films were showing a photo sensitive ferroelectric behaviour with a notable apparent polarization in the range of 10–15 μC/cm2. These films also exhibited a switchable photo-response and this parameter was observed to be sensitive to polarisation field and the polarization direction. The device shows a large ON/OFF photo current ratio with an open circuit voltage of 0.14 V. The photo response at zero bias of this BFTO based heterostructures showed rapid increase to a saturation value of 6 μA at zero bias.

Ferroelectric photovoltaic properties in doubly substituted (Bi0.9La0.1)(Fe0.97Ta0.03)O3 thin films

Doubly substituted [Bi0.9La0.1][Fe0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. The ferroelectric photovoltaic properties of ZnO:Al/BLFTO/Pt thin film capacitor structures were evaluated under white light illumination. The open circuit voltage and short circuit current density were observed to be ∼0.20 V and ∼1.35 mA/cm2, respectively. The band gap of the films was determined to be ∼2.66 eV, slightly less than that of pure BiFeO3 (2.67 eV). The PV properties of BLFTO thin films were also studied for various pairs of planar electrodes in different directions in polycrystalline thin films.

Dielectric properties and electrical conduction of high-k LaGdO3 ceramics

The temperature and frequency dependent dielectric properties and leakage conduction mechanism in LaGdO3 (LGO) ceramics have been studied, and this material has been identified as a potential high-k candidate for the future complementary metal-oxide-semiconductor (CMOS) and dynamic random access memory (DRAM) technology nodes. The dielectric constant and the loss tangent at 100 kHz were ∼21.5 and ∼0.003, respectively, at ambient conditions without any significant temperature and voltage dependence. The ac conductivity shows the typical features of universal dynamic response (UDR) and obey the double power law σac=σdc+Aωn1+Bωn2 with three types of temperature dependent conduction processes involved; (i) a dc plateau (< 3 kHz) due to long range translational hopping, (ii) a mid frequency region due to the short range hopping (3–100 kHz), and (iii) a high frequency region due to localized or reorientational hopping (100–1000 kHz). The temperature dependent dc conductivity follows the Arrhenius relation with ...

Optical properties of amorphous high-k LaGdO3 films and its band alignment with Si

Optical properties of pulsed laser ablated amorphous high-k LaGdO3 (LGO) thin films on quartz (0001) substrates and its conduction/valance band offset with Si were studied. Complex refractive index and bandgap were extracted from the transmission spectra. An increase in the bandgap with decreasing film thickness was observed. The degree of structural disorder frozen in the network was estimated using Urbach model and found that the amorphousness increased with decreasing thickness. The analysis of refractive index dispersion with wavelength confirmed the single-effective-oscillator model for the direct inter-band transition. The calculated conduction and valance band offset of LGO with silicon were 2.57 ± 0.15 eV and 1.91 ± 0.15 eV, respectively, and are high enough to suppress the electron or hole injection into the conduction and valence band of LGO from the Si substrate, hence, can be of use as new high-k dielectric for the Si based CMOS technology.