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Due to the high refractive index of nitrides, encapsulation is necessary to improve the light extraction efficiency for GaN-based light-emitting diodes (LEDs). Traditional thermal-curing encapsulant needs to be heated for several minutes to form a dome-shaped lens, which is time-consuming. In this paper, we have developed a novel kind of silicon-based ultraviolet (UV)-curing encapsulant, for which only 20 s of near-UV (NUV) light radiation at room temperature is needed. The composition of the encapsulants is optimized to enhance light extraction ability. For 392-nm NUV LEDs packaged by this UV-curing encapsulant, the light output power is enhanced by 10.0%. Moreover, the LEDs packaged by UV-curing and thermal-curing encapsulant presented similar stability and reliability after 480 h of the aging test under a high driving current of 200 mA. This paper demonstrates the potential of silicon-based UV-curing encapsulants for the package of NUV, blue and white LEDs, which is time- and cost-effective for the LED industry. [ABSTRACT FROM AUTHOR]

We designed and fabricated AlGaN-based near-ultraviolet light-emitting diodes (LEDs) operating at 368 nm with high output power using Ta2O5/SiO2 hybrid distributed Bragg reflectors (DBRs). The output powers of LEDs with eight-pair DBR and hybrid-DBR configurations were increased by 18% and 25% when compared with that of an LED without any DBR. The reflectance of the eight-pair DBR and hybrid-DBR were as high as 99%. In addition, the reflectance of the fabricated hybrid-DBR showed a slight dependence on the incident light wavelength and the angle of incidence. In comparison to the eight-pair DBR, the bandwidth of the hybrid-DBR’s reflectance band was broadened by up to 74 nm. Under current injection at 350 mA, output powers of 88, 104, and 110 mW were measured for LEDs without any DBR reflector, with the eight-pair DBR, and with the hybrid-DBR, respectively. [ABSTRACT FROM PUBLISHER]

A nonvolatile memory (NVM) based on an amorphous-indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) with defect-engineered gate insulator was demonstrated. The gate insulator was a blocking alumina/storage alumina/tunneling alumina stack structure, which was simply assembled in a single atomic layer deposition step. The memory device showed a positive shift of threshold voltage as large as 14.4 V after +20 V, 1 s programming. In contrast, the memory erasing was not sensitive to negative gate voltage in the dark. Once programmed, the memory can only be light erased. Furthermore, the light combined with a negative bias improved the erasing speed effectively. In addition, a 10-year memory window as large as 7.5 V was extrapolated at room temperature with a charge loss of 34.7%. Based on the observation of blisters in the storage alumina layer after high temperature annealing, Fourier transform infrared spectroscopy measurement and first-principles calculations, the high electron storage capacity can be attributed to the deep defect levels in the storage alumina layer, which were originated from hydrogen impurity. This a-IGZO TFT charge trapping NVM with high performance and simple process is a candidate device for the application of fully functional transparent system on panel. [ABSTRACT FROM AUTHOR]

In this study, we have systematically investigated the effect of Si doping level in the n-cladding layer on the performance of InGaN/GaN-based light-emitting diodes (LEDs). Detailed structural, optical and electrical properties of the sample with different Si doping level were studied. Based on these investigations, it was found that with a low level of Si doping (0.738 nmol/min, \sim \5.4\times \10^17\ \cm^3), the subsequent multiple-quantum-well (MQW) structure showed superior crystalline quality with low-density threading dislocations (TDs); however, the operation voltage of the LED chips became unbearable. On the other hand, the highly-doped (14.40 nmol/min, \sim \1.1\times \10^19\ \cm^3) samples showed a substantially lower operation voltage, but the MQW quality deteriorated with much higher TD density. Finally, the effect of inserting a 100-nm-thick undoped spacer GaN layer between the n-cladding layer and active layers was also investigated. The electrical and emission properties both deteriorated while the crystalline quality improved for LEDs with this structure, proving the importance of electron injection on the performance of LEDs. [ABSTRACT FROM PUBLISHER]

We report the observation of electroluminescence from the first to fourth quantum wells (QWs) from the p-GaN layer in InGaN/GaN multiple-QW light-emitting diodes (LEDs) with various indium contents (4%–16%) in each QW. The investigated LED sample showed a lower turn-on voltage and ideality factor as well as a reduction of etching pit density compared with the reference sample. Also, the X-ray reciprocal space maps revealed a partial strain relaxation in the active region. The enhanced hole injection efficiency was attributed to the weakening of strain-induced polarization field in the QWs and the good crystalline quality. [ABSTRACT FROM PUBLISHER]

The lateral current spreading (CS) effect on the efficiency droop in GaN-based LEDs has been studied in terms of the CS distance (LCS) using a designed pattern with the 2-D current spreading profile. The correlations of CS effect with the electrical, luminescent and electric-thermal properties of the LEDs have been discussed. LEDs with the LCS longer than the theoretically calculated effective CS length (Leff) suffer from more serious efficiency droop and the degradation of luminescent properties. However, the influence of CS effect on the ideality factors of LEDs is not obvious. Higher chip temperature caused by poor CS was observed and may further enlarge the efficiency droop. [ABSTRACT FROM PUBLISHER]

The performance of InGaN/GaN multiple quantum wells (MQWs) blue light-emitting diodes (LEDs) was improved by inserting a thin Mg-delta-doped hole injection layer at the end of the MQWs. The forward- and reverse-leakage currents were significantly reduced compared with those of the LEDs without the inserting layer. The light output power was enhanced by 13% at a 350 mA injection current. The improved performance could be ascribed to the dislocation suppression and hole concentration enhancement in the p-type GaN by inserting the Mg-delta-doped structure. [ABSTRACT FROM PUBLISHER]

In this letter, InGaN/GaN multiquantum well LEDs were fabricated with aluminum-doped zinc oxide (AZO) transparent conductive layer (TCL) grown by metal organic chemical vapor deposition (MOCVD) on n+-InGaN contact layer. Ultralow forward voltage ( V\!f ) of 2.86 V at 20 mA was obtained, attributing to the epitaxial-like excellent interface between AZO/n+-InGaN contact layer confirmed by high-resolution transmission electron microscopy. The most worthy is that the V\!f uniformity can be demonstrated on a 2-in wafer with a standard deviation of 0.02 V. Combined with the excellent light extraction, the MOCVD grown AZO-TCL is expected to be an alternative of tin-doped indium oxide in GaN-based LEDs for mass production. [ABSTRACT FROM AUTHOR]