Final Report Summary - SNB09 (Substrate nanopatterning by e-beam lithography to growth-ordered arrays of III-nitride nanodetectors: application to IR detectors, emitters, and new solar cells)
Within this project we developed new technologies to growth-ordered arrays of nitride nanosized columns. These nanosized columns find many applications in high-efficiency nano-optoelectronic devices such as photodetectors, light-emitting diodes (LEDs) and solar cells. This 'ordered' growth, where the nanocolumns nucleate and grow in pre-determined surface sites, gives the benefit of having arrays of nanocolumns perfectly distributed in a controlled way, all with the same diameter and height. All these features were demonstrated, on the one hand, to significantly improve the optical and electrical properties of crystalline GaN / InGaN nano-heterostructures. On the other hand, homogeneous heights favoured the top merging of the nanocolumns both to create a flat pseudo-substrate with low defect density, and to further process the ensemble into a real device.
Different types of nitride nano-heterostructures of different size and shape have been obtained. These ordered arrays of nanorods were used to demonstrate novel photonic devices, which go beyond the state of the art. These devices are interband and intersubband nanophotodetectors based on GaN / InGaN nanorods containing QDiscs. The spectral range of interest extends from near infrared (NIR) to visible and ultraviolet (UV). We took profit of the excellent transport and optical properties of defect-free nitride nanorods for fabricating efficient nanodevices in the form of single-wire detectors or ordered arrays of nanodetectors. Another two achievements of the project are the development of efficient red, green, and blue light emitters, and eventually of white light emitters for general lighting. Also, we have developed ordered arrays of InGaN / GaN / Si p-i-n nanodiodes that have important applications in the solar cell industry. All these applications used the same building blocks, that is, arrays of nanorod heterostructures grown in an ordered, controlled fashion.
Within the framework of this project we developed new technologies in terms of controlled growth of III-nitride heterostructure nanorods by plasma-assisted molecular beam epitaxy (PA-MBE) and processing of nanodevices arrays. The single-rod photoconductive devices along with their emitter counterparts offered prospects for novel photonic architectures of great interest for on-chip optical data communication systems. From a fundamental point of view, we could get access to the unique interband and intersubband properties of single Qdisc heterostructures by probing the photocurrent in a single nanorod. In turn, ordered arrays of nanophotodetectors pave the way for efficient devices, which will benefit both from the excellent photoconductive properties of single defect-free nanorods as well as from an enhanced light coupling efficiency through grating effects. The photodetector arrays can also be used for focal plane imagers in the UV (solar-blind cameras) and NIR (IR cameras). The underlying technology offers prospects to realise many other nanodevices such as organised arrays of LEDs or nanolasers, as well as very efficient solar cells. In that respect, one of the major issues that rely on the ordered growth is the use of nanostructured compound semiconductors, i.e. Ga(In)N, for low-cost, power-efficient light sources for the general lighting market. To master this highly inter-disciplinary task, the field of nanorod emitters grown on cheap Si substrates is just appearing at the horizon. Thus reaching device efficiencies that demonstrated the high potential of this approach provides a tremendous step forward.
From the photovoltaic point of view, the InGaN material system was investigated to achieve high efficiency solar cells, using arrays of nanocells based on InGaN p-i-n (QW) nanorod heterostructures grown by MBE on conductive substrates (Si and GaN templates), and processed into mesa devices. This approach offers the advantages of defect-free, high quality material, and a much larger surface for light absorption. Although processing into real devices is still ongoing, from single p-i-n nanocolumns data we could see a tremendous efficiency improvement with respect to compact layers and self-assembled nanocolumns. The outcome of this project is very innovative and original in all aspects, from the control of localised growth by MBE of nanorod heterostructures, and the quite new nature of such columnar heterostructures (including QDiscs, QDots), to the applications in well-known fields but following disruptive strategies. The results of this project not only are highly innovative, and aiming to fill technological and scientific gaps in photonics and optoelectronics areas, but they also propose very new solutions as devices (demonstrators) that go well beyond the state of the art. It is worth to mention again that the use of ordered arrays of nanodevices is beyond the frontier of the actual knowledge and technological achievements.
In order to reach the project objectives, novel concepts, approaches and methods were employed. Among them, new materials and nanostructures, new growth mechanisms and strategies (localised growth), and new concepts materialised in brand new devices whose structure and very promising performance were tested for the first time. Due to their innovation, the contributions of this project, both in terms of scientific / technological achievements, and the social / economic impact, are outstanding. The proposed areas for applications are extremely useful and prone to mass production: optical communications, general lighting purposes, and energy conversion. All three will have a tremendous impact on people's daily needs and lives. In addition, it is worth to say that the very nature of the materials used, the III-nitrides, being non pollutant and harmless to human health (no phosphorous, mercury, arsenic, etc.) are most adequate for the purpose of widespread public applications.
The project was presented when the development of the main targeted objectives was brand new and emerging. In addition, the search for environmental safe, non-pollutant devices to cover energy conversion, lighting and communication areas is of very high relevance. As mentioned before, the material system used was free of common harmful chemicals, like arsenic, phosphorous and mercury. In a moment where the energy saving protocols are more and more demanding, the development of white emitters with extremely low consumption and long life, or the design and fabrication of new solar cells with efficiencies well beyond the state of the art, are of great relevance and interest. The benefit of undertaking this project within the Community was twofold: first, new breakthrough technologies were developed, that promoted industrial development, and second, a huge gain in scientific knowledge and competitiveness towards the United States of America (USA) and Japan, very active countries in the areas exposed, was reached. Moreover, the device demonstrators linked the project to industrial processes and interests.
Different types of nitride nano-heterostructures of different size and shape have been obtained. These ordered arrays of nanorods were used to demonstrate novel photonic devices, which go beyond the state of the art. These devices are interband and intersubband nanophotodetectors based on GaN / InGaN nanorods containing QDiscs. The spectral range of interest extends from near infrared (NIR) to visible and ultraviolet (UV). We took profit of the excellent transport and optical properties of defect-free nitride nanorods for fabricating efficient nanodevices in the form of single-wire detectors or ordered arrays of nanodetectors. Another two achievements of the project are the development of efficient red, green, and blue light emitters, and eventually of white light emitters for general lighting. Also, we have developed ordered arrays of InGaN / GaN / Si p-i-n nanodiodes that have important applications in the solar cell industry. All these applications used the same building blocks, that is, arrays of nanorod heterostructures grown in an ordered, controlled fashion.
Within the framework of this project we developed new technologies in terms of controlled growth of III-nitride heterostructure nanorods by plasma-assisted molecular beam epitaxy (PA-MBE) and processing of nanodevices arrays. The single-rod photoconductive devices along with their emitter counterparts offered prospects for novel photonic architectures of great interest for on-chip optical data communication systems. From a fundamental point of view, we could get access to the unique interband and intersubband properties of single Qdisc heterostructures by probing the photocurrent in a single nanorod. In turn, ordered arrays of nanophotodetectors pave the way for efficient devices, which will benefit both from the excellent photoconductive properties of single defect-free nanorods as well as from an enhanced light coupling efficiency through grating effects. The photodetector arrays can also be used for focal plane imagers in the UV (solar-blind cameras) and NIR (IR cameras). The underlying technology offers prospects to realise many other nanodevices such as organised arrays of LEDs or nanolasers, as well as very efficient solar cells. In that respect, one of the major issues that rely on the ordered growth is the use of nanostructured compound semiconductors, i.e. Ga(In)N, for low-cost, power-efficient light sources for the general lighting market. To master this highly inter-disciplinary task, the field of nanorod emitters grown on cheap Si substrates is just appearing at the horizon. Thus reaching device efficiencies that demonstrated the high potential of this approach provides a tremendous step forward.
From the photovoltaic point of view, the InGaN material system was investigated to achieve high efficiency solar cells, using arrays of nanocells based on InGaN p-i-n (QW) nanorod heterostructures grown by MBE on conductive substrates (Si and GaN templates), and processed into mesa devices. This approach offers the advantages of defect-free, high quality material, and a much larger surface for light absorption. Although processing into real devices is still ongoing, from single p-i-n nanocolumns data we could see a tremendous efficiency improvement with respect to compact layers and self-assembled nanocolumns. The outcome of this project is very innovative and original in all aspects, from the control of localised growth by MBE of nanorod heterostructures, and the quite new nature of such columnar heterostructures (including QDiscs, QDots), to the applications in well-known fields but following disruptive strategies. The results of this project not only are highly innovative, and aiming to fill technological and scientific gaps in photonics and optoelectronics areas, but they also propose very new solutions as devices (demonstrators) that go well beyond the state of the art. It is worth to mention again that the use of ordered arrays of nanodevices is beyond the frontier of the actual knowledge and technological achievements.
In order to reach the project objectives, novel concepts, approaches and methods were employed. Among them, new materials and nanostructures, new growth mechanisms and strategies (localised growth), and new concepts materialised in brand new devices whose structure and very promising performance were tested for the first time. Due to their innovation, the contributions of this project, both in terms of scientific / technological achievements, and the social / economic impact, are outstanding. The proposed areas for applications are extremely useful and prone to mass production: optical communications, general lighting purposes, and energy conversion. All three will have a tremendous impact on people's daily needs and lives. In addition, it is worth to say that the very nature of the materials used, the III-nitrides, being non pollutant and harmless to human health (no phosphorous, mercury, arsenic, etc.) are most adequate for the purpose of widespread public applications.
The project was presented when the development of the main targeted objectives was brand new and emerging. In addition, the search for environmental safe, non-pollutant devices to cover energy conversion, lighting and communication areas is of very high relevance. As mentioned before, the material system used was free of common harmful chemicals, like arsenic, phosphorous and mercury. In a moment where the energy saving protocols are more and more demanding, the development of white emitters with extremely low consumption and long life, or the design and fabrication of new solar cells with efficiencies well beyond the state of the art, are of great relevance and interest. The benefit of undertaking this project within the Community was twofold: first, new breakthrough technologies were developed, that promoted industrial development, and second, a huge gain in scientific knowledge and competitiveness towards the United States of America (USA) and Japan, very active countries in the areas exposed, was reached. Moreover, the device demonstrators linked the project to industrial processes and interests.