Chenna Dhanavantri

Realization of Long-Period Corrugated Grating in Silica-on-Silicon-Based Channel Waveguide

Long-period corrugated grating in silica-on-silicon-based channel waveguide is realized by making periodic corrugation on top of a relatively high-indexed (contrast ap.8%) Ge-doped silica waveguide, which is sandwiched between undoped silica undercladding and boro-phospho-silicate-glass overcladding layers. Resonance wavelength of the 15-mm-long grating is found at ~1581 nm, having negligible polarization dependency at room temperature, with a grating strength of ~11 dB and 3-dB bandwidth of 7 nm. The temperature characteristic of the grating is also investigated, which is found to be similar to that of the long-period fiber grating. This device has significant potential for various integrated-optic communication and sensing applications.

Optimization of p-GaN/InGaN/n-GaN Double Heterojunction p-i-n Solar Cell for High Efficiency: Simulation Approach

We have conducted numerical simulation of p-GaN/In0.12Ga0.88N/n-GaN, p-i-n double heterojunction solar cell. The doping density, individual layer thickness, and contact pattern of the device are investigated under solar irradiance of AM1.5 for optimized performance of solar cell. The optimized solar cell characteristic parameters for cell area of 1  × 1 mm2 are open circuit voltage of 2.26 V, short circuit current density of 3.31 mA/cm2, fill factor of 84.6%, and efficiency of 6.43% with interdigitated grid pattern.

A study on the 2D simulation of Pt/InGaN/GaN/metal Schottky junction solar cell

We report on the 2D simulation of the heterojunction-based M/InxGa1-xN/GaN/M Schottky junction solar cell and studied the variations of different factors such as indium mole fraction, thickness, temperature and doping density of the n-InxGa1-xN active layer on the solar cell performance. The current–voltage characteristics have been simulated at various temperatures, in the range from 100 to 700 K. The results show that the value of all the characteristic parameters such as open-circuit voltage, fill factor and conversion efficiency, except short-circuit current density, decreases with increasing temperature. The barrier height and ideality factor of the Pt/In0.21Ga0.79N/GaN/M Schottky junction solar cell have been evaluated from current–voltage characteristics and at 300 K they are 0.53 eV and 0.39, respectively. The photovoltaic output under AM0 sunlight illumination of the optimized Schottky junction solar cell at room temperature is 0.58 V (open-circuit voltage), 5.36 mA cm−2 (short-circuit current density), 67% (fill factor) and 1.55% (conversion efficiency). The behavior of these parameters with the underlying physics is presented.

The Effect of Indium Composition on Open-Circuit Voltage of InGaN Thin-Film Solar Cell: An Analytical and Computer Simulation Study

In this work we have evaluated the open-circuit voltage developed across a metal/n-InGaN Schottky junction solar cells through both analytical and computer simulation as a function of varying indium composition. Our study includes four different systems such as Au/n-InGaN/Al, Pd/n-InGaN/Al, Ni/n-InGaN/Al and Pt/n-InGaN/Al with a variation of Indium composition. It is reported that there exists a certain value of Indium composition which decides the InGaN as a Schottky junction solar cell. This cut-off value of Indium is calculated for all the systems by analytical and simulated approach and a comparison is also made between them. The difference of 19.4% for Au, 18.91% for Pd, 20.50% for Ni and 15.15% for Pt between analytical and simulation is reported.

Improved light extraction efficiency of InGaN/GaN blue LED by patterning free surfaces

The light extraction efficiency of GaN/InGaN based blue LED is improved by using hexagonal facets on n- and p- free surfaces and on substrate interfaces. Light interaction with patterned surfaces having hexagonal facets significantly improved the light extraction efficiency. The simulated results show that the light extraction efficiency is drastically improved from 18.08% to 89.27% by patterning the free surfaces.

Tunable and wavelength selective PIN diodes

Wavelength Division Multiplexing has become the leading technology for optical transmission systems which operate at 1550 nm. One of the key components of such systems are tunable and wavelength selective receivers. In this paper we present a fibre-coupled two-chip receiver front end, which is highly wavelength selective and tunable over a wide wavelength range. The device is a bulk-micromachined Fabry-Perot pin-photodiode, which features a high finesse of more than 220 with a sufficient tuning range (> 40 nm) to cover wide wavelength region. The bandwidth (full-width half maximum) of the device is < 0.2 nm (25 GHz). The photocurrent crosstalk from an adjacent channel (100 GHz spaced apart) is below -30 dB. The wavelength tuning is achieved by a change in the resonator length, formed by the two chips. This is realized by current induced thermal heating on top of the membrane mirror suspensions, which deflects the membrane. The optical-electrical conversion takes place in the pin-photodiode. This integration reduces the need for any additional components. Fiber-coupling is achieved with a fiber-coupled lens that tailors the Gaussian beam to match with the Fabry-Perot cavity. The alignment process of the two-chip structure, forming the wavelength selective cavity, has been simplified to the point where a simple place-and-fix strategy can be applied.

Top- and Bottom-Patterned GaN/InGaN Violet Light Emitting Diode Structure for Enhanced Light Extraction

Micro-patterning is carried out on top-surface of GaN/InGaN violet LEDs grown on patterned sapphire substrates (PSS). Electro-luminescence/ light-output of hexagonal hole-type and grating-type LEDs are found 1.8/2.0 and 1.4/1.5 times higher compared to conventional LED respectively.

Theoretical analysis of blue to white down conversion for light-emitting diode light with yttrium aluminum garnet phosphor

Abstract. The down conversion of blue to white light with yttrium aluminum garnet (YAG) phosphor is analyzed theoretically for GaN/InGaN light emitting diodes. A cerium-doped YAG phosphor with particle size of ∼10  μm having peak emission wavelength of 560 nm is considered in this study. Effects of phosphor concentration, thickness of the conversion medium, excitation spectrum, and driving current are studied in terms of luminous efficacy and the quality of white light emission. It has been observed that the above parameters have a significant effect on chromaticity coordinates. Ray-tracing simulation results show that the luminous efficacy of down-converted white light is found to be 3.25 times the blue light excitation with phosphor concentration of 2.10E7  cm−3 and thickness of 30 μm for an injection current density of 10  A/cm2. A stable cool white light having correlated color temperature in a range of 5500–5600 K is achieved for the proposed optimized design for the variation of ambient temperatures from −25°C to 150°C.

Fabrication and characterization of InGaN/GaN MQWs blue light-emitting diodes on sapphire substrate

In this paper, we report successful fabrication and characterization of InGaN/GaN MQWs based blue LEDs on c-plane sapphire substrate. The epitaxial material used in the fabrication of blue LEDs was grown by metal-organic-chemical vapor deposition (MOCVD) system. The threshold voltage (Vth) of fabricated InGaN/GaN MQWs blue LED on c-plane sapphire substrate was ~ 3.1 V.

Grid contact optimization of p-i-n GaN/InGaN solar cell

In this study, we have conducted numerical simulations to design the device contact pattern for the optimized performance of InGaN p-i-n solar cells. GaN/InGaN p-i-n solar cell studied with two different contact patterns, with grid pattern and without grid pattern. Solar characteristic parameters for both geometries are simulated with 1 × 1 mm2 device areas while varying grid spacing and number of grids. An improved efficiency from 4.16 % to 6.34 % is observed with grid pattern and with optimized grid spacing of 225 microns.