Periodic Reporting for period 2 - ReSensE (Reversed-polarity III-nitride Sensors for Enhanced UV-detection)
Reporting period: 2022-07-01 to 2023-06-30
The Action “ReSensE” (Reversed-polarity III-nitride Sensors for Enhanced UV-detection) aims at developing a new type of semiconductor material, and at its use for enabling more efficient sensors of ultraviolet light.
III-nitride materials (GaN, InN, AlN and their alloys) constitute a very well-known semiconductor system, with tremendous industrial applications from energy-saving LED bulbs and lasers, to the next generation of high-frequency transistors for wireless telecommunication.
To make these devices available to the benefit of the general public, though, scientists need first to be able to synthesize the materials from their atomic constituents. This is done through a process called epitaxy, in which the atoms that form the materials are stacked, layer by layer, in a controlled way, using specially designed reactors at very high temperatures. In theory, the atom stacking sequence of these materials can be done in two possible ways (or polarities), but one of them is much easier to control and almost always used.
However, III-nitride materials grown with the standard polarity have internal electric fields oriented in a direction that is very detrimental to the operation of most devices. For this reason, ReSensE wants to develop new epitaxial techniques for growing III-nitride materials with reversed polarity (the so-called nitrogen-polarity). In addition to that, ReSensE investigates the use of these new materials in highly-efficient UV sensors, which could be used in flame detection systems for fire prevention, as well as in many other applications such as control of industrial processes, diagnostic equipment, and space explorations.
III-nitride materials (GaN, InN, AlN and their alloys) constitute a very well-known semiconductor system, with tremendous industrial applications from energy-saving LED bulbs and lasers, to the next generation of high-frequency transistors for wireless telecommunication.
To make these devices available to the benefit of the general public, though, scientists need first to be able to synthesize the materials from their atomic constituents. This is done through a process called epitaxy, in which the atoms that form the materials are stacked, layer by layer, in a controlled way, using specially designed reactors at very high temperatures. In theory, the atom stacking sequence of these materials can be done in two possible ways (or polarities), but one of them is much easier to control and almost always used.
However, III-nitride materials grown with the standard polarity have internal electric fields oriented in a direction that is very detrimental to the operation of most devices. For this reason, ReSensE wants to develop new epitaxial techniques for growing III-nitride materials with reversed polarity (the so-called nitrogen-polarity). In addition to that, ReSensE investigates the use of these new materials in highly-efficient UV sensors, which could be used in flame detection systems for fire prevention, as well as in many other applications such as control of industrial processes, diagnostic equipment, and space explorations.
During the Outgoing Phase of ReSensE, which has been carried out at Nagoya University in Japan, high quality nitrogen polar GaN and AlN templates have been successfully demonstrated.
In addition to that, a significant amount of work has been done to gain a deeper understanding of the physical mechanisms behind the epitaxy of nitrogen polar III-nitride materials. Thanks to these insights, the growth of nitrogen polar III-nitride materials can be controlled more efficiently, fine tuned, and transferred to different reactors. The new epitaxial techniques developed during the Outgoing Phase have been successfully adapted and replicated with the MOVPE reactor available at Tyndall National Institute in Cork, Ireland, during the Return Phase.
A new hybrid strategy for the reduction of threading dislocations in nitrogen-polar heterostructures has bee developed. This approach consists in a specially-designed microscale patterning of the initial epilayer, and subsequent epitaxial lateral overgrowth to form a smooth planar layer of improved crystal quality.
The above described technical achievements enable the realization of a novel, cost-effective, solar-blind UV-detector based on AlGaN/AlGaN heterostructure on sapphire. The development of a strategy for the commercialization of this novel device has also been part of the Action.
In addition to that, a significant amount of work has been done to gain a deeper understanding of the physical mechanisms behind the epitaxy of nitrogen polar III-nitride materials. Thanks to these insights, the growth of nitrogen polar III-nitride materials can be controlled more efficiently, fine tuned, and transferred to different reactors. The new epitaxial techniques developed during the Outgoing Phase have been successfully adapted and replicated with the MOVPE reactor available at Tyndall National Institute in Cork, Ireland, during the Return Phase.
A new hybrid strategy for the reduction of threading dislocations in nitrogen-polar heterostructures has bee developed. This approach consists in a specially-designed microscale patterning of the initial epilayer, and subsequent epitaxial lateral overgrowth to form a smooth planar layer of improved crystal quality.
The above described technical achievements enable the realization of a novel, cost-effective, solar-blind UV-detector based on AlGaN/AlGaN heterostructure on sapphire. The development of a strategy for the commercialization of this novel device has also been part of the Action.
While nitrogen polar GaN is a relatively well-established material, work is still needed to fully understand how to control its epitaxy and further improve its quality. On the other hand, nitrogen polar AlN is still at its infancy and very few groups have been able to demonstrate smooth and high-quality epitaxy, and, to the best of our knowledge, we are one of the only two who have achieved it on sapphire substrates. The contribution of ReSensE to the development of this new technological approach is hence significant.
One of the main factors that has so far hindered the application of nitrogen-polar III-nitride materials to optoelectronic devices (as opposed to electronic devices where they are already well established) is the difficulty in achieving sufficient crystal quality. With the new technique developed for the reduction of threading dislocations in nitrogen-polar heterostructures, the Action "ReSensE" has enabled the demonstration of nitrogen-polar GaN templates with the best crystal quality ever reported for epilayers grown on sapphire.
One of the main factors that has so far hindered the application of nitrogen-polar III-nitride materials to optoelectronic devices (as opposed to electronic devices where they are already well established) is the difficulty in achieving sufficient crystal quality. With the new technique developed for the reduction of threading dislocations in nitrogen-polar heterostructures, the Action "ReSensE" has enabled the demonstration of nitrogen-polar GaN templates with the best crystal quality ever reported for epilayers grown on sapphire.