DUV-LEDs with a single EBL, graded EBL, and graded superlattice EBL were demonstrated using the high-temperature metal organic chemical vapor deposition system. A DUV-LED with a GSL-EBL showed improved carrier injection into the multi-quantum well region.

We report deep ultraviolet (UVC) emitting core-shell-type AlGaN/AlN multiple quantum wells (MQWs) on the AlN nanorods which are prepared by catalyst/lithography free process. The MQWs are grown on AlN nanorods on a sapphire substrate by polarity-selective epitaxy and etching (PSEE) using hightemperature metal organic chemical vapor deposition. The AlN nanorods prepared through PSEE have a low dislocation density because edge dislocations are bent toward neighboring N-polar AlN domains. The core-shell-type MQWs grown on AlN nanorods have three crystallographic orientations, and the final shape of the grown structure is explained by a ball-and-stick model. The photoluminescence (PL) intensity of MQWs grown on AlN nanorods is approximately 40 times higher than that of MQWs simultaneously grown on a planar structure. This result can be explained by increased internal quantum efficiency, large active volume, and increase in light extraction efficiency based on the examination in this study. Among those effects, the increase of active volume on AlN nanorods is considered to be the main reason for the enhancement of the PL intensity.Aluminum nitride (AlN) based devices operating in the deep ultraviolet (UVC) regime (200-280 nm) have attracted considerable attention owing to their wide range of potential applications such as medical therapy, UV curing, biochemical sensing, water or air purification, and disinfection 1-3 . However, AlN based UVC devices still suffer from low quantum efficiency and output power. Although the external quantum efficiency of UVC light-emitting diodes (LEDs) has increased dramatically lately, most of the reported efficiency values remain at a few percent of the commercially required level. The low internal quantum efficiency due to a high dislocation density 4,5 and polarization coefficient 6,7 is the bottleneck for high-performance UVC applications.Such critical obstacles can be surmounted by introducing three-dimensional (3D) nanostructures because of their high stress relaxation, low dislocation density, increased active volume, and high extraction efficiency 8,9 . However, AlN based nanostructures for UVC light emitters have seldom been investigated because of the difficulty of using patterned masks. Selective area growth is strongly inhibited because Al atoms have very high sticking coefficient. Zhao et al. recently reported that these difficulties can be addressed by employing nitrogen (N)-polar Al(Ga)N nanowires grown on a Si substrate using a lithography-free process 10 . They developed self-organized AlN nanowire LEDs operating at 210 nm, the shortest wavelength ever reported for a nanostructure, and also reported an AlN nanowire laser diode fabricated by radio-frequency plasma-assisted molecular beam epitaxy (MBE) 9,11 . However, AlN or sapphire substrates are preferable for devices operating in the UVC regime because they are transparent to UVC emission. The polarity of the AlN layer can be controlled by varying the preflow conditions before AlN growth and the annealing temperature...

In this paper, a gradient electron blocking layer (GEBL) is introduced to improve efficiency of deep‐ultraviolet light‐emitting diodes (DUV‐LEDs). Various structures of DUV‐LEDs are simulated to determine the energy band diagram variation and carrier injection mechanism resulting from the insertion of the GEBL. The simulation results show the improved electron and hole transport behavior in AlGaN multi quantum wells (MQWs). Especially, the injection efficiency of holes is improved with the increasing number of GEBL steps, which lead to the enhancement of internal quantum efficiency (IQE). The DUV‐LED structures with GEBL are grown in a high‐temperature metal‐organic chemical vapor deposition (HT‐MOCVD) system. Electroluminescence (EL) spectra show that the emission intensity at a wavelength of 280 nm from a DUV‐LED with a 12‐steps EBL is about 2.3 times that from a DUV‐LED with a single EBL.

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The present study investigated the Mg doping effect in the gallium nitride (GaN) buffer layers (BLs) of AlGaN/GaN high-electron-mobility transistor (HEMT) structures grown on semi-insulating 4H-SiC substrates by metal organic chemical vapor deposition. When the Mg concentration was increased from 3 × 1017 to 8 × 1018 cm−3, the crystal quality slightly deteriorated, whereas electrical properties were significantly changed. The buffer leakage increased approximately 50 times from 0.77 to 39.2 nA at −50 V with the Mg doping concentration. The Mg-compensation effect and electron trapping effect were observed at Mg concentration of 3 × 1017 and 8 × 1018 cm−3, respectively, which were confirmed by an isolation leakage current test and low-temperature photoluminescence. When the BL was compensated, the two-dimensional electron gas (2DEG) mobility and sheet carrier concentration of the HEMTs were 1560 cm2 V−1 s−1 and 5.06 × 1012 cm−2, respectively. As a result, Mg-doped GaN BLs were demonstrated as a candidates of semi-insulating BLs for AlGaN/GaN HEMT.

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Large area deep ultraviolet (DUV) light is generated by carbon nanotube (CNT) cold cathode electron beam (C-beam) irradiation on Al0.47Ga0.53N/Al0.56Ga0.44N multi quantum wells (MQWs) anode. We developed areal electron beam (EB) with CNT cold cathode emitters. The CNT emitters on silicon wafer were deposited with an area of 188 mm2, and these were vertically aligned and had conical structures. We optimized the C-beam irradiation conditions to effectively excite AlGaN MQWs. When AlGaN MQWs were excited using an anode voltage of 3 kV and an anode current of 0.8 mA, DUV with a wavelength of 278.7 nm was generated in a large area of 303 mm2. This DUV area is more than 11 times larger than the light emitting area of conventional EB pumped light sources and UV-LEDs.

Herein, the effect of crystal quality of AlN buffer layer on AlGaN/GaN/AlN double‐heterostructure high‐electron‐mobility transistor (DH‐HEMT) is investigated. The material quality of the GaN channel and the AlGaN barriers, such as the dislocation density and the interface roughness, deteriorates, and the 2D electron gas (2DEG) mobility decreases as the threading dislocation density (TDD) of the AlN buffer increases. It is also revealed that the thickness and the Al mole fraction of the AlGaN barrier are affected by the strain variation of the GaN channel depending on the TDD of the AlN buffer. The variation of the compressive strain of the GaN channel is responsible for the 2DEG density change by affecting the barrier condition and the piezoelectric polarization charge. Low‐temperature Hall effect measurement reveals that the interface roughness scattering is a dominant factor for the mobility of the DH‐HEMT, which is ≈2–6 × 103 cm2 (V s)−1.