Shruti Verma

Blue electroluminescence from Sb-ZnO/Cd-ZnO/Ga-ZnO heterojunction diode fabricated by dual ion beam sputtering

p-type Sb-doped ZnO/i-CdZnO/n-type Ga-doped ZnO was grown by dual ion beam sputtering deposition system. Current-voltage characteristics of the heterojunction showed a diode-like rectifying behavior with a turn-on voltage of ~5 V. The diode yielded blue electroluminescence emissions at around 446 nm in forward biased condition at room temperature. The emission intensity increased with the increase of the injection current. A red shifting of the emission peak position was observed with the increment of ambient temperature, indicating a change of band gap of the CdZnO active layer with temperature in low-temperature measurement.

Benzo[ghi]perylene monoimide based photosensitive lamellar Cd-doped ZnO nanohybrids

Lamellar hybrid inorganic/organic nanostructures comprising of alternating layers of benzo[ghi]perylene monoimide and Cd-doped ZnO called BPyM/CZO nanohybrids have been synthesized electrochemically on Ga-doped ZnO/Si. In order to study the effect of organic surfactant, inorganic CZO nanorods have also been electrochemically synthesized. The role of annealing and organic surfactant on morphology, structure, composition and opto-electronic properties is analyzed. The nanohybrids and nanorods are c-axis oriented preferentially with their (002) direction perpendicular to the substrate surface. Annealed BPyM/CZO nanohybrids show visible orange photoluminescence emission while unannealed nanohybrids and inorganic CZO nanorods emit white emission at room temperature. The annealed nanohybrids and inorganic nanorods tend to follow the Varshni equation with temperature variation from 80 K to 300 K. Spectroscopic ellipsometry reveals the thickness, refractive index and band gap of the nanostructures. Annealing tends to expand the band gap by 50 meV in the case of inorganic CZO nanorods, but shrinks the band gap by 20 meV for BPyM/CZO nanohybrids. Temperature dependent photosensitivity measurements reveal that BPyM/CZO nanohybrids are highly photosensitive, ∼8 fold and ∼4 fold higher than inorganic CZO nanorods at 80 K and 300 K, respectively. The studies indicate that BPyM/CZO nanohybrids hold potential as photosensors.

Effect of Growth Temperature on Properties of CdZnO Thin Films

Ternary CdZnO thin films were grown on sapphire substrate with varied growth temperature from 300 to 600 °C using dual ion-beam sputtering system. The structural, morphological and optical properties of the films were deeply studied. X-ray Diffraction (XRD) measurements indicate phase separation in the deposited CdZnO films. The photoluminescence studies indicate emission centered around 440 nm ~ 2.8 eV. The optical band gap was confirmed by UV–Vis spectrometric measurements. It was also found that band gap narrows down with the increase in growth temperature.

Investigation on Hybrid Green Light-Emitting Diode

We propose a hybrid light-emitting diode (LED) design comprising of p-GaN/ p-MgZnO/ InGaN/ n-MgZnO/ n-ZnO emanating green electroluminescence centered around 560 nm. We compare the performance of proposed LED with ZnO and GaN based green LEDs through 2-D numerical simulation. It is found that hybrid LED shows highest IQE of 93.2 % with added advantage of least efficiency droop at high injection current.

Impact of Auger recombination on hybrid green light-emitting diode

The Auger recombination is considered to be one of the reasons for the origin of efficiency droop in InGaN-based light-emitting diodes (LEDs). We discuss, through numerical simulation, the impact of Auger recombination on internal quantum efficiency (IQE), luminous power and electroluminescence intensity of hybrid green light-emitting diode. The simulation results indicate that large values of Auger recombination coefficient decreases IQE greatly. Also, electron leakage is found to be a contributing factor towards efficiency droop at high injection current.

High performance from ZnO multiple quantum-well green light emitting diode with Li-doped CdZnO active region

A comprehensive theoretical study of Cd0.4Zn0.6O/ZnO multiple quantum-well (MQW) based light emitting diode (LED) is performed using a commercial TCAD simulation software. A device internal quantum efficiency (IQE) of ~94% is achieved at room temperature from such LED that, emanates at 510 nm wavelength with a turn-on voltage of 3.1 V. The effects of thickness, doping, and alloy composition of various device constituent layers are comprehensively studied while optimizing the device performance at room temperature. It is also observed that electroluminescence (EL) intensity increased by a factor of 1.25 Li doping (doping concentration=1×1018 cm-3) of CdZnO well region, possibly due to the strain-induced piezoelectric polarization and spontaneous polarization reduction caused by Li ferroelectric dipole moment.

CIGS thin film Deposition by Dual Ion Beam Sputtering (DIBS) system for Solar cell Applications

Currently in solar cell market the cost effective Copper Indium Gallium Selenide (i.e. Cu(In,Ga)Se2 or CIGS) thin film solar cells are showing most promising result among all other thin film solar cell technology. Typically, CIGS thin films for photovoltaic devices are deposited by co-evaporation or by deposition of the metals with or followed by treatment in a selenium environment. These methods have several disadvantages and complications. In this article, we describe an alternative of the same. We described the CIGS thin films of 1 μm thickness grown onto soda lime glass substrates by Dual Ion Beam Sputtering (DIBS) system from a single quaternary target with the composition of Cu (In0.70Ga0.30)Se2 in a single step route without any additional selenization at different temperatures from 100 °C to 400 °C. These CIGS thin films are characterized for the solar cell application. The effects of the substrate temperature, on the structural and optical property of the CIGS layers were studied at room temperature using X-Ray Diffraction and UV–Vis-NIR spectrophotometer. The obtained results of the thin films includes the crystallinity, grain size, absorption coefficient and band gap energy etc. In structural property the preferred orientation of grains along highly oriented the (112) plane is observed. Crystallinity of the films improved with increasing substrate temperature as evidenced by the decrease of FWHM from 0.64 °C to 0.29 °C The strong influence of growth temperature on these properties were observed. We demonstrated that growth temperature can be varied in order to optimize the film properties and improve device performance.