C. Mukherjee

Effect of excess plasma on photoelectron spectra of nanoporous GaP

A comparative study of the effect of excess plasma on the photoelectron spectra (PES) of crystalline gallium phosphide (GaP) wafer and “nanoporous” GaP network samples have been carried out. Rigid shift along with large changes in the line shapes of PES of nanoporous GaP have been observed in the presence of secondary light with respect to spectra measured in its absence. In case of GaP wafer, only rigid shift of PES have been observed. The valence bands offset between “nanoporous” GaP and GaOx is found 2.30eV at 300K.

Investigation of metal nanoparticles on a Si surface using an x-ray standing wave field

An x-ray standing wave field generated under total external reflection condition is used to characterize the average vertical dimension of metal nanoparticles as well as their nature of dispersion on a flat surface. This approach is applied to characterize the distribution of Fe nanoparticles deposited on a silicon surface using a solution dip method. The atomic force microscopy results on these nanoparticles reinforce our interpretation. The authors believe that the present method has a strong utility in characterizing, over a large area, the morphology of the surfaces coated with nanoparticles. The method also provides element specific analysis for the nanoparticulate matter.

Plasmon generation in sputtered Ga-doped MgZnO thin films for solar cell applications

The crystalline, electrical, morphological, optical properties and plasmonic behaviour of Ga doped MgZnO (GMZO) thin films grown at different substrate temperatures (200–600 °C) by a dual ion beam sputtering (DIBS) system are investigated. Transmittance value of more than ∼94% in 400–1000 nm region is observed for all GMZO films. The particle plasmon features can be detected in the absorption coefficient spectra of GMZO grown at 500 and 600 °C in the form of a peak at ∼4.37 eV, which corresponds to a plasmon resonance peak of nanoclusters formed in GMZO. The presence of such plasmonic features is confirmed by ultraviolet photoelectron spectroscopy measurements. The values of particle plasmon resonance energy of various nanoclusters are in the range of solar spectrum, and these can easily be tuned and excited at the desirable wavelengths while optimizing the efficiency of solar cells (SCs) by simple alteration of DIBS growth temperature. These nanoclusters are extremely promising to enhance the optical sca...

Localized surface plasmon resonance on Au nanoparticles: tuning and exploitation for performance enhancement in ultrathin photovoltaics

We report a detailed correlation analysis of the size, shape, and distribution of Au nanoparticles (NPs) on fine-tuning of localized surface plasmon resonance and optical absorption cross-section. Experimental analysis of annealing temperature and initial Au layer thickness on NP parameters such as size, interparticle distance, surface coverage, and circularity factor has been studied. The effect of annealing on the morphological, structural, dielectric, and elemental behavior of Au NPs has been reported. Theoretically, we have analyzed the tuning of LSPR and absorption cross-section peaks by varying NP parameters, surrounding medium, and substrate. This report is critical in terms of predicting performance enhancement of ultrathin photovoltaics with varied cell architectures.

Band alignment and photon extraction studies of Na-doped MgZnO/Ga-doped ZnO heterojunction for light-emitter applications

Ultraviolet photoelectron spectroscopy is carried out to measure the energy discontinuity at the interface of p-type Na-doped MgZnO (NMZO)/n-type Ga-doped ZnO (GZO) heterojunction grown by dual ion beam sputtering. The offset values at valence band and conduction band of NMZO/GZO heterojunction are calculated to be 1.93 and −2.36 eV, respectively. The p-type conduction in NMZO film has been confirmed by Hall measurement and band structure. Moreover, the effect of Ar+ ion sputtering on the valence band onset values of NMZO and GZO thin films has been investigated. This asymmetric waveguide structure formed by the lower refractive index of GZO than that of NMZO indicates that easy extraction of photons generated in GZO through the NMZO layer into free space. The asymmetric waveguide structure has potential applications to produce ZnO-based light emitters with high extraction efficiency.

Role of Plasmons in Improved Photovoltaic Devices : Nano Clusters of Sn and SnOx in SnO2 Films

Recently, plasmonic concepts have been used to increase absorption length of incident light and seperation of excess carriers in photovoltaic devices. Doped SnO2 films are used as transparent conducting oxide (TCO) in photovoltaic devices. Sputter etched surfaces of SnO2 films have nano clusters of Sn and SnOx. Valence bulk plasmons (VBPs) of nano clusters have been studied using ultraviolet photoelectron spectroscopy (UPS) in in-situ conditions. Transmission and atomic force microscopy (AFM) are used in ex-situ conditions to study surface morphology and optical properties of sputtered SnO2 thin films.

Band alignment study and plasmon generation at dual ion-beam sputtered Ga:ZnO/ Ga:MgZnO heterojunction interface

A flat band offset at 3 atomic% Ga-doped ZnO (GZO)/1 atomic% Ga-doped Mg0.05Zn0.95O (GMZO) interface is obtained with valence and conduction band offset values of -0.045 and -0.065 eV, respectively. The materials are grown by dual ion-beam sputtering (DIBS) system, and the values of band offsets at the interface are calculated by ultraviolet photoelectron spectroscopy measurement. It is observed that the band offset can be further tuned by suitable band-gap engineering by changing the elemental composition of Mg and Ga in ZnO or by altering DIBS growth parameters. Moreover, generation of plasmons in individual GZO and GMZO films due to the formation of metal and metal oxide nanoclusters are observed. This is promising in terms of increasing the efficiency of the solar cell by increasing optical path length in the absorbing layer by light scattering and trapping mechanism.