InGaN nanowires for Electroluminescents Diodes – FIDEL

With a worldwide electric power consumption close to 20% for general lighting, the set up of low consumption light sources is a one of possible answer to the greenhouse effect problem. From OIDA (Optoelectronic Industry Development Association) point of view, the transition from incandescent light bulbs to light emitting diodes (LEDs) based systems would allow an economy of around 50% of the consumed annual electric power consumption. However a dramatic cost reduction and performance increase is still needed to observe LED penetration in general lighting.
The aim of the FIDEL project is to study the use of nanowires as starting structures for LEDs. The use of nanowire type structures would allow overcoming different technological obstacles for efficient LED realization compatible with general lighting market requirements in term of cost and performances:

1. The high specific surface of nanowires would allow an efficient stress relaxation:
a. nanowires can be grown on large size silicon substrates
b. the In content inside the the nanowire could be higher than for planar layers; the use of nanowires would allow to fulfil what is usually called the “green gap”, i.e. the absence of high brightness LEDs emitting in the green range.
2. Their three dimensional structure would allow to increase the emitting surface and thus the light emitted for a given surface chip.
3. Unlike sapphire used in actual technologies, silicon is an excellent electrical and thermal conductor.
4. Nanowires have a good crystalline quality.
5. Nanowires used in core/shell structure (heterostructures along m plane) will eliminate what is called “Quantum confined Stark effect” which decreases radiative efficiency by spatial separation of electron and hole wave functions.
6. Realization of native or monolithic white LEDs, i.e. without phosphors:
a. Cost reduction
b. Higher performances by conversion efficiency elimination
c. Better device reliability

The implementation of this technological breakthrough would accelerate the cost reduction and improve LED energetic efficiency. Within the framework of this project, we will address mainly the green gap problematic by studying innovative nanowire architecture. The main goal of this project is to establish the luminous emission efficiency variation as function of wavelength increase in the green, yellow, or red range.

At the beginning, this project will lean on experience acquired since several years within CEA on growth, characterization and technological process of nanoLEDs based on III-nitride materials with, particularly, light emitting device realization at the state of the art. Different epitaxial techniques will be tested, namely molecular beam epitaxy, metal organic vapour phase epitaxy, and finally in a more exploratory way, hydrides vapour phase epitaxy. Several tools for structural, electrical and optical characterization, and particulary specific techniques for nanowires allowing determining single nanowire properties (transmission electronic microscopy, micro-photoluminescence, lithography by electronic beams, cathodoluminescence, electron beam induced current, …) are already available within the consortium.
The implementation of these two platforms -growth and characterization- is one of the key for the success of this project. We will have access within the consortium to all necessary means to realize growths, and to characterize them. In addition, result promotion is planned through a start-up, HelioDEL which is in now in process in CEA. The goal of this company is the realization and the commercialization of nanoLEDs for general lighting.