anirban dhar - Academia.edu (original) (raw)
Papers by anirban dhar
Journal of Applied Physics, 1998
Radio frequency magnetron sputtered Ba0.8Sr0.2TiO3 thin films have been deposited on silicon and ... more Radio frequency magnetron sputtered Ba0.8Sr0.2TiO3 thin films have been deposited on silicon and Si/SiO2/SiN/Pt substrates. The analysis of plasma discharge has been carried out using the Langmuir probe technique. Both the pressure and power have been found to influence the ion density and self-bias of the target. Introduction of oxygen into the discharge effectively decreases the ion density. The structural and electrical properties have been investigated using x-ray diffraction, atomic force microscopy of deposited films and capacitance-voltage, conductance-voltage, and current density-electric field characteristics of fabricated capacitors. The growth and orientation of the films have been found to depend upon the type of substrates and deposition temperatures. The <100> texture in the film is promoted at a pressure 0.25 Torr with a moderately high value of ion density and low ion bombardment energy. Films deposited on Si/SiO2/SiN/Pt substrate have shown higher dielectric constant (191) and lower leakage current density (2.8×10-6 A/cm2 at 100 kV/cm) compared to that on silicon.
Journal of Applied Physics, 2007
CdS nanocomposites have been grown in a polymer ͑polyvinyl alcohol͒ matrix using a simple chemica... more CdS nanocomposites have been grown in a polymer ͑polyvinyl alcohol͒ matrix using a simple chemical bath deposition process. Transmission electron micrographs of nanocomposites grown at different solution temperatures revealed the formation of isolated as well as junctionlike structures. X-ray and selected area electron diffraction patterns show that the nanocomposites are polycrystalline with cubic CdS phase. Optical band gaps of nanocomposite films are found to decrease ͑3.26-2.86 eV͒ with the increase in bath temperature from 70 to 90°C. Photoluminescence spectra show strong green emission attributed to the Cd 2+ or Cd + ion-related recombination via moderately deep trap states. The nanocomposites show an enormous enhancement of dielectric constant in polyvinyl alcohol matrix over a frequency range of 40 Hz-10 MHz.
Physica B-condensed Matter, 2007
Journal of Physics D-applied Physics, 2010
... [1] Tang CW 1986 Appl. Phys. Lett. 48 183 [2] Shaheen SE, Brabec CJ, Sariciftci NS, Padinger ... more ... [1] Tang CW 1986 Appl. Phys. Lett. 48 183 [2] Shaheen SE, Brabec CJ, Sariciftci NS, Padinger F, Fromherz T and Hummelen JC 2001 Appl. Phys. Lett. 78 841 ... Phys. Lett. 90 253502 [14] Castro FA, Benmansour H, Graeff CFO, Nesch F, Tutis E and Hany R 2006 Chem. Mater. ...
Journal of Physics D-applied Physics, 2009
The photovoltaic properties of devices based on a new combination, pentacene/[6,6]-phenyl C61 but... more The photovoltaic properties of devices based on a new combination, pentacene/[6,6]-phenyl C61 butyric acid methyl ester (PCBM) bilayer hetero-junctions, were investigated. The crystallinity of pentacene was found to be improved by depositing a PEDOT : PSS layer on an indium tin oxide substrate, which in turn doubled the power conversion efficiency of the device. The PCBM layer showed a significant contribution to the device photocurrent, which originated mainly due to the dissociation of excitons at the pentacene/PCBM interface. By optimizing the thickness of the pentacene and PCBM layers, a broader photo-response was obtained in the external quantum efficiency spectra indicating efficient light harvesting throughout the visible region of the solar spectrum.
Journal of Applied Physics, 2007
Polycrystalline Ba1-xSrxTiO3 (BST) thin films with three different compositions have been deposit... more Polycrystalline Ba1-xSrxTiO3 (BST) thin films with three different compositions have been deposited by radio-frequency magnetron sputtering technique on platinum coated silicon substrates. Samples with buffer and barrier layers for different film thicknesses and processing temperatures have been studied. Crystallite size of BST films has been found to increase with increasing substrate temperature. Thickness dependent dielectric constant has been studied and discussed in the light of an interfacial dead layer and the finite screening length of the electrode. Ferroelectric properties of the films have also been studied for various deposition conditions. The electrical resistivity of the films measured at different temperatures shows a positive temperature coefficient of resistance under a constant bias voltage.
Journal of Applied Physics, 1996
A simple single-source electron-beam evaporation technique has been used for the deposition of le... more A simple single-source electron-beam evaporation technique has been used for the deposition of lead-lanthanum-zirconate-titanate (PLZT) thin films for silicon-based device applications. An optimized annealing condition has been established for the formation of crystalline perovskite phases. The effect of the bottom electrodes and the barrier layer on the growth of the films has been studied. Films with good dielectric and optical
Applied Physics Letters, 2004
Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, ... more Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, sputtered SiGe layers and thermally grown tunnel oxide were fabricated on p-Si substrates. The trilayer structures were rapid thermal annealed at 1000 °C in nitrogen atmosphere for different durations. Cross-sectional transmission electron micrographs revealed the complete isolation of Ge nanocrystals in the sandwiched structure annealed for a longer duration. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. Under optimized annealing conditions, an enhancement of the charge storage capability of nanocrystals was observed in agreement with the optical emission characteristics.
Applied Physics Letters, 2003
The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surf... more The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surfaces have been investigated using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. N2O-plasma-treated films show the formation of a nitrogen-rich Zr-germano-silicate interfacial layer between the deposited ZrO2 and SiGeC films. The N-treated film has a higher accumulation capacitance (~1200 pF), lower leakage current density (7×10-9 A/cm2at-1 V), higher breakdown field (~11 MV/cm), and higher interfacial layer dielectric constant (~10) than that of the non-nitrogen-treated films. Relatively lower positive trap charge generated by a constant current stressing in N-incorporated dielectric films makes it attractive for scaled metal-oxide-semiconductor field-effect transistor applications.
Journal of Applied Physics, 2007
A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of ... more A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of Ge nanostructures on Au-coated Si (100) substrates. The formation of Ge nanodots, nanorods, and nanowires has been observed at different growth temperatures. The diameter of grown nanowires is found to be varying from 40 to 80 nm and that of nanorods from 70 to 90 nm, respectively. A comparative study has been done on three types of samples using x-ray diffraction and Raman spectroscopy. Photoluminescence spectra of grown nanostructures exhibit a broad emission band around 2.6 eV due to oxide related defect states.
Applied Physics Letters, 2003
Ultrathin ZrO2 gate dielectrics have been deposited on strain-compensated Si0.69Ge0.3C0.01 layers... more Ultrathin ZrO2 gate dielectrics have been deposited on strain-compensated Si0.69Ge0.3C0.01 layers by rf magnetron sputtering. High-resolution transmission electron microscopy along with energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy show the formation of a polycrystalline ZrO2 and an amorphous Zr-germano-silicate interfacial layer between the deposited oxide and SiGeC films. A dielectric constant of 17.5 for ZrO2 and 7.0 for an interfacial-silicate layer have been calculated from the high-frequency capacitance-voltage measurements. These dielectrics show an equivalent oxide thickness as low as 1.9 nm for ZrO2 and 2.0 nm for the interfacial silicate layer. An extremely low leakage current density of ~9×10-8 A/cm2 at a gate voltage of -1.0 V, breakdown field of 7 MV/cm and moderate interface state density of 6×1011 cm-2 eV-1 have been obtained for the fabricated capacitors.
Journal of Physics D-applied Physics, 2008
Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sp... more Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO2 insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO2 buffer layer. The electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO2 layer. The MFIS structure exhibits a maximum clockwise C-V memory window of 1.60 V when the thickness of the HfO2 layer was 12 nm with a lower leakage current density of 6.20 × 10-7 A cm-2 at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer-ferroelectric interface is studied by the voltage stress method. Capacitance-voltage (C-V) and leakage current density (J-V) characteristics of the Al/SBT/HfO2/Si(1 0 0) capacitor indicate that the introduction of the HfO2 buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO2/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure is ideally suitable for high performance ferroelectric memories.
Journal of Physics D-applied Physics, 2007
Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have ... more Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have been analysed using impedance spectroscopy (100 Hz-20 MHz) and dc-current versus voltage measurements. Conduction mechanisms match well with the space charge limited current model with exponential trap charge distributions. Impedance studies reveal the Schottky behaviour for both the devices. The differences between p-Si/pentacene/Al and ITO/pentacene/Al devices have been explained by modelling equivalent circuits, with one and two RC elements, respectively. The switch-over field from ohmic conduction to space charge limited conduction, charge concentration as a function of voltage and bias dependent series resistance have been estimated for both the cases.
Journal of Applied Physics, 1998
Radio frequency magnetron sputtered Ba0.8Sr0.2TiO3 thin films have been deposited on silicon and ... more Radio frequency magnetron sputtered Ba0.8Sr0.2TiO3 thin films have been deposited on silicon and Si/SiO2/SiN/Pt substrates. The analysis of plasma discharge has been carried out using the Langmuir probe technique. Both the pressure and power have been found to influence the ion density and self-bias of the target. Introduction of oxygen into the discharge effectively decreases the ion density. The structural and electrical properties have been investigated using x-ray diffraction, atomic force microscopy of deposited films and capacitance-voltage, conductance-voltage, and current density-electric field characteristics of fabricated capacitors. The growth and orientation of the films have been found to depend upon the type of substrates and deposition temperatures. The <100> texture in the film is promoted at a pressure 0.25 Torr with a moderately high value of ion density and low ion bombardment energy. Films deposited on Si/SiO2/SiN/Pt substrate have shown higher dielectric constant (191) and lower leakage current density (2.8×10-6 A/cm2 at 100 kV/cm) compared to that on silicon.
Journal of Applied Physics, 2007
CdS nanocomposites have been grown in a polymer ͑polyvinyl alcohol͒ matrix using a simple chemica... more CdS nanocomposites have been grown in a polymer ͑polyvinyl alcohol͒ matrix using a simple chemical bath deposition process. Transmission electron micrographs of nanocomposites grown at different solution temperatures revealed the formation of isolated as well as junctionlike structures. X-ray and selected area electron diffraction patterns show that the nanocomposites are polycrystalline with cubic CdS phase. Optical band gaps of nanocomposite films are found to decrease ͑3.26-2.86 eV͒ with the increase in bath temperature from 70 to 90°C. Photoluminescence spectra show strong green emission attributed to the Cd 2+ or Cd + ion-related recombination via moderately deep trap states. The nanocomposites show an enormous enhancement of dielectric constant in polyvinyl alcohol matrix over a frequency range of 40 Hz-10 MHz.
Physica B-condensed Matter, 2007
Journal of Physics D-applied Physics, 2010
... [1] Tang CW 1986 Appl. Phys. Lett. 48 183 [2] Shaheen SE, Brabec CJ, Sariciftci NS, Padinger ... more ... [1] Tang CW 1986 Appl. Phys. Lett. 48 183 [2] Shaheen SE, Brabec CJ, Sariciftci NS, Padinger F, Fromherz T and Hummelen JC 2001 Appl. Phys. Lett. 78 841 ... Phys. Lett. 90 253502 [14] Castro FA, Benmansour H, Graeff CFO, Nesch F, Tutis E and Hany R 2006 Chem. Mater. ...
Journal of Physics D-applied Physics, 2009
The photovoltaic properties of devices based on a new combination, pentacene/[6,6]-phenyl C61 but... more The photovoltaic properties of devices based on a new combination, pentacene/[6,6]-phenyl C61 butyric acid methyl ester (PCBM) bilayer hetero-junctions, were investigated. The crystallinity of pentacene was found to be improved by depositing a PEDOT : PSS layer on an indium tin oxide substrate, which in turn doubled the power conversion efficiency of the device. The PCBM layer showed a significant contribution to the device photocurrent, which originated mainly due to the dissociation of excitons at the pentacene/PCBM interface. By optimizing the thickness of the pentacene and PCBM layers, a broader photo-response was obtained in the external quantum efficiency spectra indicating efficient light harvesting throughout the visible region of the solar spectrum.
Journal of Applied Physics, 2007
Polycrystalline Ba1-xSrxTiO3 (BST) thin films with three different compositions have been deposit... more Polycrystalline Ba1-xSrxTiO3 (BST) thin films with three different compositions have been deposited by radio-frequency magnetron sputtering technique on platinum coated silicon substrates. Samples with buffer and barrier layers for different film thicknesses and processing temperatures have been studied. Crystallite size of BST films has been found to increase with increasing substrate temperature. Thickness dependent dielectric constant has been studied and discussed in the light of an interfacial dead layer and the finite screening length of the electrode. Ferroelectric properties of the films have also been studied for various deposition conditions. The electrical resistivity of the films measured at different temperatures shows a positive temperature coefficient of resistance under a constant bias voltage.
Journal of Applied Physics, 1996
A simple single-source electron-beam evaporation technique has been used for the deposition of le... more A simple single-source electron-beam evaporation technique has been used for the deposition of lead-lanthanum-zirconate-titanate (PLZT) thin films for silicon-based device applications. An optimized annealing condition has been established for the formation of crystalline perovskite phases. The effect of the bottom electrodes and the barrier layer on the growth of the films has been studied. Films with good dielectric and optical
Applied Physics Letters, 2004
Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, ... more Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, sputtered SiGe layers and thermally grown tunnel oxide were fabricated on p-Si substrates. The trilayer structures were rapid thermal annealed at 1000 °C in nitrogen atmosphere for different durations. Cross-sectional transmission electron micrographs revealed the complete isolation of Ge nanocrystals in the sandwiched structure annealed for a longer duration. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. Under optimized annealing conditions, an enhancement of the charge storage capability of nanocrystals was observed in agreement with the optical emission characteristics.
Applied Physics Letters, 2003
The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surf... more The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surfaces have been investigated using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. N2O-plasma-treated films show the formation of a nitrogen-rich Zr-germano-silicate interfacial layer between the deposited ZrO2 and SiGeC films. The N-treated film has a higher accumulation capacitance (~1200 pF), lower leakage current density (7×10-9 A/cm2at-1 V), higher breakdown field (~11 MV/cm), and higher interfacial layer dielectric constant (~10) than that of the non-nitrogen-treated films. Relatively lower positive trap charge generated by a constant current stressing in N-incorporated dielectric films makes it attractive for scaled metal-oxide-semiconductor field-effect transistor applications.
Journal of Applied Physics, 2007
A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of ... more A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of Ge nanostructures on Au-coated Si (100) substrates. The formation of Ge nanodots, nanorods, and nanowires has been observed at different growth temperatures. The diameter of grown nanowires is found to be varying from 40 to 80 nm and that of nanorods from 70 to 90 nm, respectively. A comparative study has been done on three types of samples using x-ray diffraction and Raman spectroscopy. Photoluminescence spectra of grown nanostructures exhibit a broad emission band around 2.6 eV due to oxide related defect states.
Applied Physics Letters, 2003
Ultrathin ZrO2 gate dielectrics have been deposited on strain-compensated Si0.69Ge0.3C0.01 layers... more Ultrathin ZrO2 gate dielectrics have been deposited on strain-compensated Si0.69Ge0.3C0.01 layers by rf magnetron sputtering. High-resolution transmission electron microscopy along with energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy show the formation of a polycrystalline ZrO2 and an amorphous Zr-germano-silicate interfacial layer between the deposited oxide and SiGeC films. A dielectric constant of 17.5 for ZrO2 and 7.0 for an interfacial-silicate layer have been calculated from the high-frequency capacitance-voltage measurements. These dielectrics show an equivalent oxide thickness as low as 1.9 nm for ZrO2 and 2.0 nm for the interfacial silicate layer. An extremely low leakage current density of ~9×10-8 A/cm2 at a gate voltage of -1.0 V, breakdown field of 7 MV/cm and moderate interface state density of 6×1011 cm-2 eV-1 have been obtained for the fabricated capacitors.
Journal of Physics D-applied Physics, 2008
Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sp... more Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO2 insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO2 buffer layer. The electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO2 layer. The MFIS structure exhibits a maximum clockwise C-V memory window of 1.60 V when the thickness of the HfO2 layer was 12 nm with a lower leakage current density of 6.20 × 10-7 A cm-2 at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer-ferroelectric interface is studied by the voltage stress method. Capacitance-voltage (C-V) and leakage current density (J-V) characteristics of the Al/SBT/HfO2/Si(1 0 0) capacitor indicate that the introduction of the HfO2 buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO2/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure is ideally suitable for high performance ferroelectric memories.
Journal of Physics D-applied Physics, 2007
Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have ... more Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have been analysed using impedance spectroscopy (100 Hz-20 MHz) and dc-current versus voltage measurements. Conduction mechanisms match well with the space charge limited current model with exponential trap charge distributions. Impedance studies reveal the Schottky behaviour for both the devices. The differences between p-Si/pentacene/Al and ITO/pentacene/Al devices have been explained by modelling equivalent circuits, with one and two RC elements, respectively. The switch-over field from ohmic conduction to space charge limited conduction, charge concentration as a function of voltage and bias dependent series resistance have been estimated for both the cases.