Fabrication of (In)GaN nanopillar arrays for solar water splitting and hydrogen generation applications (GaNPEC)

Research summary

The production of hydrogen by solar energy is an attractive technique to realize global renewable energy supply. The photoinduced water splitting into hydrogen and oxygen by the direct use of sunlight is an ideal, renewable method of hydrogen production that integrates solar energy collection and water electrolysis into a single photoelectrode. Although the concept is attractive to produce sustainable fuel, the suitable electrode material (performance, stability and low cost) is yet to be found.

Description

To address this challenge, we will use III-nitride semiconductor nanostructures. III-nitride semiconductors have emerged as a new class of materials for photoelectrochemical water splitting and hydrogen production. The energy band gap of these nitride semiconductors can be tuned to cover nearly the entire solar spectrum. Moreover the band edge potentials of these nitride semiconductors straddle the redox potentials of water over a large composition range. On the other hand, the nanopillar (NP) structures, the energy conversion can be improved by high surface to volume ratio, low defect density and enhanced charge separation. The goal of proposed project is to dramatically increase the efficiency of photoelectrochemical cell by 1) finding the ideal composition and crystal direction of III-N semiconductors to absorb a significant portion of the solar spectrum and to conduct charge efficiently, 2) identifying the III-N nanostructure geometry optimal for the application of water splitting 3) developing fabrication methods, and theoretical models needed to manufacture and optimize devices and exhibiting long-term stability in an aqueous solution.

The nanostructures are fabricated in Finland. IIT, India is concentrating on the performance of GaN and InGaN nanopillar based Photo Electric cells.
First the epitaxial layers of GaN and InGaN were grown on sapphire substrates using MOVPE technique. The InxGa1-xN layer having different In contents (from 10% to 50%) were grown and the nanopillar arrays will be fabricated using the nanomasking and RIE techniques. The nanomasking was done using Ni nanoparticle formation. After this reactive ion etching (RIE) is used to etch down GaN and InGaN nanopillar arrays. The entire process for nanomasking and etching was optimized. The most critical issue in real applications of GaN nanopillar by Ni nanomask technique is typically the RIE etching process. The RIE etching process causes damage to the sidewall of the GaN nanopillars. We have investigated the effect of rf power, chamber pressure and gas flow rates in order to avoid the plasma-induced damage in GaN nanopillars. After the fabrication of nanopillar arrays, detailed characterization of these samples was carried out using techniques such as XRD, SEM/TEM, Raman, photoluminescence. Using these techniques we have obtained information about the morphology, surface damage/defects, stress, and surface composition.
The good quality GaN and InGaN nanopillar arrays is utilized as anode in the photoelectrochemical (PEC) cell for the water splitting application. Presently, We try to increase the photocurrent density and solar-to-hydrogen efficiency of the PEC cell. Moreover, the stability of these nanopillar arrays in acidic/alkaline solutions will be checked using long term photocurrent generation experiments. The comparison of the PEC cell performance using GaN and InGaN in planar as well as in nanopillar geometry will be carried out in order to see the effect of enhanced surface-to-volume ratio in the latter case.

We have made our joint publication. We have studied the temperatre dependent electrical properties of GaN diode. The paper is accepted and in press now.

Research info

Research title
Fabrication of (In)GaN nanopillar arrays for solar water splitting and hydrogen generation applications (GaNPEC)

Research timeline
1.2.2014 - 1.11.2016

Keywords
Hydrogen generation nanotechnology Photoelectro chemical cell

Region
Asia

Countries
Finland, India

Institution
Aalto University
Department of Micro and Nanosciences
ESPOO, Finland

Funding instrument
Other

Project budget
0 - 200,000 euros

Head of research
Nagarajan Subramaniyam

Research team
Nagarajan Subramaniyam (Finland), Markku Sopanen (Finland), Rajendra singh (India), Ashutosh Kumar (India)

Partners
Indian Institute of Technology, Delhi, India

Contact information
Prof. Rajendra Singh
91-11-2659 6495
rsingh@physics.iitd.ac.in

Record last updated
31.8.2015