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Schematic illustration of a nitride-based MIS UV LED structure.
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Strong room-temperature electroluminescence at 365 nm has been demonstrated from simple Au/AlN/n-GaN metal-insulator-semiconductor (MIS) light emitting diodes (LEDs), which do not contain p-doped material. Current-voltage (IV) and electroluminescence (EL) data indicate that an AlN insulating layer thickness of 10 nm results in optimised diode behav...
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... by the poorly optimised doping and the low epitaxial quality of the films. Therefore, this study aims to develop an efficient nitride-based resonant tunnelling light emitting diode using high-quality material, and investigate the efficiencies and operating mechanisms of resonant tunnelling MIS LEDs based on an Au/AlN/n-GaN heterostructure. Fig. 1 shows a schematic of the MIS UV LED device structure, with a 0.45 mm 2 mesa. An active layer comprising a 2 m n-type Si-doped GaN (carrier concentration: 6×10 18 cm -3 ) was grown by metal-organic chemical vapour deposition (MOCVD) on a 3 m unintentionally- doped GaN buffer layer with a low dislocation density of 1 × 10 8 cm -2 , ...
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... Notable among these is a report by Lin et al. on GaN MIS emitters operating via a resonant tunneling mechanism. 7) The shortest wavelength reported in their work was limited to approximately 360 nm. Another recent report on the III-nitride MIS structure is that of Taniyasu et al., whose MIS diode emitted at 210 nm. 2) In their implementation of the concept, AlN served as the semiconductor layer. ...
Al-rich III–nitride-based deep-ultraviolet (UV) (275–320 nm) light-emitting diodes are plagued with a low emission efficiency and high turn-on voltages. We report Al-rich (Al,Ga)N metal–insulator–semiconductor UV light-emitting Schottky diodes with low turn-on voltages of <3 V, which are about half those of typical (Al,Ga)N p–i–n diodes. Our devices use a thin AlN film as the insulator and an n-type Al0.58Ga0.42N film as the semiconductor. To improve the efficiency, we inserted a GaN quantum-well structure between the AlN insulator and the n-type Al xGa1− xN semiconductor. The benefits of the quantum-well structure include the potential to tune the emission wavelength and the capability to confine carriers for more efficient radiative recombination.
... 12,14,15 However, as reinforced in this paper, it is also possible to use unipolar RTDs for this purpose, such as purely n-doped RTDs, where, e.g., impact ionization triggered holes are created 16 or via direct tunnelling of carriers from the valence band. 17 In this case, understanding the process of light generation and its correlation with the way the carriers are transported and scattered becomes a relevant topic to tackle. Yet, the nature of these effects is scarcely investigated since externally tunable parameters with large impact in the system response, such as the position of the resonant voltage, are usually lacking. ...
We study the electroluminescence (EL) emission of purely n-doped resonant tunneling diodes in a wide temperature range. The paper demonstrates that the EL originates from impact ionization and radiative recombination in the extended collector region of the tunneling device. Bistable current-voltage response and EL are detected and their respective high and low states are tuned under varying temperature. The bistability of the EL intensity can be switched from direct to inverted with respect to the tunneling current and the optical on/off ratio can be enhanced with increasing temperature. One order of magnitude amplification of the optical on/off ratio can be attained compared to the electrical one. Our observation can be explained by an interplay of moderate peak-to-valley current ratios, large resonance voltages, and electron energy loss mechanisms, and thus, could be applied as an alternative route towards optoelectronic applications of tunneling devices.
Aluminum nitride (AlN) film has a wide range of applications optoelectronic devices. In this paper, AlN thin films were prepared by magnetron sputtering method, the influence of substrate temperature and nitrogen-argon ratio on the structure, morphology and optical properties of AlN films were evaluated by X-ray diffractometer, scanning electron microscope and ultraviolet–visible spectrophotometer. The analysis showed that the AlN film exhibited better crystallization quality under the substrate temperature of 350 °C with a nitrogen-argon ratio of 5:40. In addition, an Au/i-AlN/n-GaN metal–insulator-semiconductor (MIS) structure device was fabricated based on high-quality AlN films. The current–voltage and electroluminescence characteristics of the device under different temperatures were studied in detail. The results showed that the device exhibited excellent rectification behavior at all operating temperatures, producing an intense UV emission (∼372 nm). This paper proposes a hole generation model and a carrier transport and recombination mechanism. The research results provide a new reference for the practical application of AlN films.
Residual stress is generated in GaN epitaxial layers due to the mismatch during GaN epitaxy on sapphire using the traditional method. Therefore, the use of graphene to reduce residual stress and dislocation densities in GaN epitaxy has become an important research direction. However, growing a stress-free GaN film on graphene substrate remains challenge. In this work, we directly grew graphene on sapphire via plasma enhanced chemical vapor deposition (PECVD) to obtain an epitaxial graphene with characteristic orientation, and ultra-low stress GaN films can then be obtained through metal organic chemical vapor deposition (MOCVD) assisted with the sputtering AlN buffer layer. Through this method, we successfully obtained continuous and flat GaN films with ultra-low biaxial compressive stress (0.023 GPa) without the complicated stress engineering during epitaxial growth. First principle calculation was employed to confirm that the characteristic orientation of epitaxial graphene is crucial to release the stress in GaN. The obtained GaN films can also be easily transferred because of small van der Waals force on graphene. The transferred GaN heterojunction was directly fabricated into a metal-insulator-semiconductor (MIS) device from which typical electrical properties can be obtained. Our work reveals the stress-releasing mechanism and excellent stress-releasing effect of graphene and provides a new epitaxial strategy to guide crystallographic epitaxy.
Negative Differential Resistance (NDR) is obtained at room temperature for Metal-Insulator-Insulator-Insulator-Semiconductor (MIIIS) diodes after band offset engineering. After post-metallization annealing (PMA), this characteristic is lost due to an inner diffusion of elements. The MIIIS diodes (as-prepared and PMA) were fabricated using a gate stack of atomic-layer deposited ultra-thin (2 nm/1 nm/2 nm) high-k oxides (Al2O3/HfO2/Al2O3) and their I-V, C-V and I-V-T characteristics were studied. A quantum well of 1.3 eV is obtained in the intermediate oxide for the as-prepared sample, promoting quantization of energy levels and resulting in three NDR zones at 0.1, 0.28 and 0.5 V due to the effects of resonant tunneling (RT). These zones are non-existent in the PMA diode. RT was found to be dominant at low voltages due to the discrete energy levels at the conduction band of the HfO2 oxide. After RT, the main conduction mechanism for both diodes is Poole-Frenkel.
