21st century light source
Light emitting diodes technology is a fast-paced field of research. Since the first compound LEDs were developed in the 50’s, efficiency and output power of the diodes improved rapidly. Howewer, as color ranges over yellow to green were available on a phosphor and aluminium basis, blue and white color LEDs were not in sight until nitride thin films got their breakthrough in the early 90’s.
LEDs on a nitride basis completed the range of primary colors and provided the first white semiconductor diodes. GaN LEDs and their alloys are currently used for specialised illumination such as stage and street lighting, displays, traffic lights or signaling.
Modern LEDs beat traditional light bulbs and fluorescent lamps by magnitudes in terms of durability and efficiency. With high power diodes available in all colours, general illumination in future will increasingly rely on these devices until traditional lighting technology will be almost completely replaced by modern LEDs.
Solving the global drinking water problem
Purification of water is one of the global challenges of the 21st century. UV LEDs on a nitride basis such as AlGaN are shown to kill bacteria and they are becoming applicable in modern purification modules. As they are more efficient than conventional mercury lamps, nitride-based LEDs will greatly enhance the performance of these devices.
While germ destruction is already shown to be satisfying at low water flow-through, the main challenge is to further increase efficiency and output power of UV LEDs to increase the purified water per minute.
A big market
The LED market is certainly the most auspicious field for nitrides. Since the first commercial GaN LEDs were shipped in 1995, the market of nitride substates has grown at an average annual rate of about 50% and it is expected to even speed up its rapid hike. The market is driven by increasing demand for blue-violet lasers and ultraviolet LEDs. As new applications become available such as blu-ray and HD DVD technology, nitride-based diodes are becoming inreasingly important – they are predicted to comprise more than one-half of the LED market at 2010 (Strategies Unlimited).
A highly versatile material
Nitride – the new silicon?
Apart from optoelectronics, gallium nitride are causing a stir in the electronics department. First GaN transistors are shown to be magnitudes more powerful than transistors based on silicon and gallium arsenide. Because of their large band gap, more voltage can be applied while yielding a high current.
Whether gallium nitride are unlikely to replace silicon in computational devices, they aim for applications where high power/high frequency is needed, e.g. in mobile phones. More power leads to higher frequency and thus, increased transmission speed. And transmission speed is in high demand – the first live-streaming mobile phones are on the road.
Modern solar cells
Indium gallium nitride cover a wide energy range of radiation. They are considered to provide alternatives to multijunction solar cells as they can be tuned to cover almost the full spectrum of sunlight. Multijunction cells currently rely on different materials to achieve this range. Howewer, composing these materials is hindered by their lattice mismatch. A big advantage of Indium gallium nitrides is their high tolerance towards lattice mismatching. In theory, efficiencies up to 70% could be achieved by composing many layers of indium gallium nitrides tuned to a range of bandgaps.
Apart from detectors in the range of blue-ultraviolet as a sideline to LED development, nitride will be used in chemical detection. Due to their piezoelectric character, gallium nitride and alloys sense differences in chemical composition of a gas or liquid by responding to the surface charge induced by polar molecules at contact.
Their ability to tolerate high temperatures and pressures makes them suitable for electronic devices such as gas detectors which can be used in rough environments, e.g. oil filled equipment.
Chemical detection is increasingly applied in medicine. First GaN sensors are used to detect changes in chemical properties of small (nanolitre) samples such as concentration or cell activity. One of the main advantages of these transistor-based devices are the great tunability. The sensors can be adjusted to respond to a certain type of substrate by modifying the transistors gate area.