Molecular beam epitaxy growth of Al-rich AlGaN nanowires for deep ultraviolet optoelectronics
TL;DR: In this paper, a new growth paradigm was proposed, wherein a precise control on the optical bandgap of ternary AlGaN nanowires can be achieved by varying the substrate temperature.
Abstract: Self-organized AlGaN nanowires by molecular beam epitaxy have attracted significant attention for deep ultraviolet optoelectronics. However, due to the strong compositional modulations under conventional nitrogen rich growth conditions, emission wavelengths less than 250 nm have remained inaccessible. Here we show that Al-rich AlGaN nanowires with much improved compositional uniformity can be achieved in a new growth paradigm, wherein a precise control on the optical bandgap of ternary AlGaN nanowires can be achieved by varying the substrate temperature. AlGaN nanowire LEDs, with emission wavelengths spanning from 236 to 280 nm, are also demonstrated.
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TL;DR: The way in which several innovative synthesis methods constitute the basis for the realization of highly controlled nanowires is reviewed, and one of how the different families ofnanowires can contribute to applications is combined.
Abstract: Low-dimensional semiconductor materials structures, where nanowires are needle-like one-dimensional examples, have developed into one of the most intensely studied fields of science and technology. The subarea described in this review is compound semiconductor nanowires, with the materials covered limited to III-V materials (like GaAs, InAs, GaP, InP,...) and III-nitride materials (GaN, InGaN, AlGaN,...). We review the way in which several innovative synthesis methods constitute the basis for the realization of highly controlled nanowires, and we combine this perspective with one of how the different families of nanowires can contribute to applications. One reason for the very intense research in this field is motivated by what they can offer to main-stream semiconductors, by which ultrahigh performing electronic (e.g., transistors) and photonic (e.g., photovoltaics, photodetectors or LEDs) technologies can be merged with silicon and CMOS. Other important aspects, also covered in the review, deals with synthesis methods that can lead to dramatic reduction of cost of fabrication and opportunities for up-scaling to mass production methods.
173 citations
TL;DR: It is demonstrated that critical issues can be potentially addressed by using nearly defect-free AlGaN tunnel junction core-shell nanowire heterostructures, which exhibit high photoluminescence efficiency in the UV-C band at room temperature and nearly one order of magnitude reduction in the device resistance.
Abstract: To date, semiconductor light emitting diodes (LEDs) operating in the deep ultraviolet (UV) spectral range exhibit very low efficiency due to the presence of large densities of defects and extremely inefficient p-type conduction of conventional AlGaN quantum well heterostructures. We have demonstrated that such critical issues can be potentially addressed by using nearly defect-free AlGaN tunnel junction core–shell nanowire heterostructures. The core–shell nanowire arrays exhibit high photoluminescence efficiency (∼80%) in the UV–C band at room temperature. With the incorporation of an epitaxial Al tunnel junction, the p-(Al)GaN contact-free nanowire deep UV LEDs showed nearly one order of magnitude reduction in the device resistance, compared to the conventional nanowire p-i-n device. The unpackaged Al tunnel junction deep UV LEDs exhibit an output power >8 mW and a peak external quantum efficiency ∼0.4%, which are nearly one to two orders of magnitude higher than previously reported AlGaN nanowire device...
120 citations
TL;DR: In this article, an electrically injected AlGaN nanowire laser operating at 239 nm at room temperature was demonstrated and the spontaneous emission coupling factor was derived to be around 0.012.
Abstract: In this work, we report on the demonstration of an electrically injected AlGaN nanowire laser operating at 239 nm at room temperature. Vertically aligned Al-rich AlGaN nanowires are grown on Si substrate by plasma-assisted molecular beam epitaxy. It is observed that the randomly distributed AlGaN nanowires can strongly confine photons in the deep ultraviolet wavelength range, due to the recurrent multiple scattering of light and the inversely tapered nanowire geometry. The laser exhibits a very low threshold current of 0.35 mA at room temperature. From the detailed rate equation analysis, the spontaneous emission coupling factor is derived to be around 0.012.
68 citations
TL;DR: In this article, the authors reported that with the use of the n+-GaN/Al/p+-AlGaN tunnel junction (TJ), the device resistance was reduced by one order of magnitude, and the light output power was increased by two orders of magnitude.
Abstract: We report AlGaN nanowire light emitting diodes (LEDs) operating in the ultraviolet-C band. The LED structures are grown by molecular beam epitaxy on Si substrate. It is found that with the use of the n+-GaN/Al/p+-AlGaN tunnel junction (TJ), the device resistance is reduced by one order of magnitude, and the light output power is increased by two orders of magnitude, compared to AlGaN nanowire LEDs without TJ. For unpackaged TJ ultraviolet LEDs emitting at 242 nm, a maximum output power of 0.37 mW is measured, with a peak external quantum efficiency up to 0.012%.
62 citations
TL;DR: The nitride-based UV nanowires light-emitting diodes (NWs-LEDs) grown on low cost and scalable metal/silicon template substrate, offers a scalable, environment friendly and low cost solution for numerous applications, such as solid-state lighting, spectroscopy, medical science and security.
Abstract: Currently the AlGaN-based ultraviolet (UV) solid-state lighting research suffers from numerous challenges. In particular, low internal quantum efficiency, low extraction efficiency, inefficient doping, large polarization fields, and high dislocation density epitaxy constitute bottlenecks in realizing high power devices. Despite the clear advantage of quantum-confinement nanostructure, it has not been widely utilized in AlGaN-based nanowires. Here we utilize the self-assembled nanowires (NWs) with embedding quantum-disks (Qdisks) to mitigate these issues, and achieve UV emission of 337 nm at 32 A/cm2 (80 mA in 0.5 × 0.5 mm2 device), a turn-on voltage of ~5.5 V and droop-free behavior up to 120 A/cm2 of injection current. The device was grown on a titanium-coated n-type silicon substrate, to improve current injection and heat dissipation. A narrow linewidth of 11.7 nm in the electroluminescence spectrum and a strong wavefunctions overlap factor of 42% confirm strong quantum confinement within uniformly formed AlGaN/AlGaN Qdisks, verified using transmission electron microscopy (TEM). The nitride-based UV nanowires light-emitting diodes (NWs-LEDs) grown on low cost and scalable metal/silicon template substrate, offers a scalable, environment friendly and low cost solution for numerous applications, such as solid-state lighting, spectroscopy, medical science and security.
60 citations
References
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TL;DR: An AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED, represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.
Abstract: The development of a compact, solid-state light-emitting diode (LED) that emits at 210 nanometres — the shortest wavelength yet achieved for any type of LED — represents an important step towards achieving exciton-related light-emitting devices and replacing inefficient gas light sources with solid-state light sources. Compact high-efficiency ultraviolet solid-state light sources1—such as light-emitting diodes (LEDs) and laser diodes—are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond2 and III–V nitride semiconductors (GaN, AlGaN and AlN; refs 3–10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride (AlN), which has a very wide direct bandgap11 of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.
1,562 citations
TL;DR: In this paper, a light-emitting diodes with emission wavelengths less than 400 nm have been developed using the AlInGaN material system, where alloy compositions with a greater aluminium content are required.
Abstract: Light-emitting diodes with emission wavelengths less than 400 nm have been developed using the AlInGaN material system. For devices operating at shorter wavelengths, alloy compositions with a greater aluminium content are required. The material properties of these materials lie on the border between conventional semiconductors and insulators, which adds a degree of complexity to the development of efficient light-emitting devices. A number of technical developments have enabled the fabrication of LEDs based on group three nitrides (III-nitrides) that emit in the UV part of the spectrum, providing useful tools for a wealth of applications in optoelectronic systems.
872 citations
TL;DR: The field of AlGaInN ultraviolet UV light-emitting diodes (LEDs) is reviewed, with a summary of the state-of-the-art in device performance and enumeration of applications.
Abstract: The field of AlGaInN ultraviolet UV light-emitting diodes (LEDs) is reviewed, with a summary of the state-of-the-art in device performance and enumeration of applications. Performance-limiting factors for high-efficiency UV LEDs are identified and recent advances in the development of deep UV emitters are presented.
644 citations
TL;DR: In this article, a transparent p-AlGaN contact layer was proposed to improve the light extraction efficiency (LEE) of DUV LEDs, and the maximum external quantum efficiency (EQE) obtained was 7% for a 279 nm DUV LED.
Abstract: In this paper, recent advances in AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) are demonstrated. 220–350-nm-band DUV LEDs have been realized by developing crystal growth techniques for wide-bandgap AlN and AlGaN semiconductors. Significant increases in internal quantum efficiency (IQE) have been achieved for AlGaN DUV emissions by developing low-threading-dislocation-density (TDD) AlN buffer layers grown on sapphire substrates. The electron injection efficiency (EIE) of the LEDs was also significantly increased by introducing a multiquantum barrier (MQB). We also discuss light extraction efficiency (LEE), which is the most important parameter for achieving high-efficiency DUV LEDs. We succeeded in improving LEE by developing a transparent p-AlGaN contact layer. The maximum external quantum efficiency (EQE) obtained was 7% for a 279 nm DUV LED. EQE could be increased by up to several tens of percent through the improvement of LEE by utilizing transparent contact layers and photonic nanostructures in the near future.
456 citations
TL;DR: In this paper, the authors used low threading dislocation density (TDD) AlN template to achieve the maximum output power of 1.1 mW and 4.0 mW for the AlGaN-QW LEDs with wavelengths of 241 nm, 256 nm, and 256 nm under room temperature (RT) CW operations.
Abstract: We demonstrate 222–282 nm AlGaN and InAlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) fabricated on low threading dislocation density (TDD) AlN template. Low TDD AlN templates were realized by using ammonia (NH3) pulse-flow multilayer (ML) growth technique. The edge- and screw-type dislocation densities of AlN layer were reduced to 7.5 × 108 and 3.8 × 107, respectively. Single-peaked electroluminescence (EL) were obtained for 222– 273 nm AlGaN multi quantum well (MQW) DUV-LEDs. We obtained the maximum output power of 1.1 mW and 4.0 mW for the AlGaN-QW LEDs with wavelengths of 241 nm, 256 nm, respectively, under room temperature (RT) CW operations. The maximum output power of 227 nm and 222 nm AlGaN-QW were 0.15 mW and 0.014 mW, respectively, under RT pulsed operation. The maximum external quantum efficiency (EQE) of the 227 nm and 250 nm AlGaN LEDs were 0.2% and 0.43%, respectively. We also fabricated 280 nm band quaternary InAlGaN-MQW DUV-LEDs with n-type and p-type InAlGaN layers on ML-AlN templates. We demonstrated extremely high internal quantum efficiency (IQE) of 284 nm InAlGaN-QW emission, which was confirmed by the fact that the ratio of the integrated intensity of the RT-PL against the 77 K-PL was 86%. The maximum output power and EQE of the 282 nm InAlGaN LED were 10.6 mW and 1.2%, respectively, under RT CW operation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
396 citations