Degradation mechanisms of 275-nm-band AlxGa1-xN multiple quantum well deep-ultraviolet light-emitting diodes fabricated on a (0001) sapphire substrate were investigated under hard operation conditions with the current of 350 mA and the junction temperature of 105 °C. The optical output power (Po) initially decreased by about 20% within the operating time less than 102 h and then gradually decreased to about 60% by 484 h. For elucidating the causes for the initial and subsequent degradations, complementary electrical, time-resolved photoluminescence (TRPL), and impurity characterizations were carried out making a connection with the energy band profiles. Because the degradation of the wells was less significant than the Po reduction, the initial degradation is attributed essentially to the decrease in carrier injection efficiency (ηinjection), not in internal quantum efficiency of the wells, most likely due to depassivation of initially H-passivated preexisting nonradiative recombination centers (NRCs) in a Mg-doped p-type Al0.85Ga0.15N electron blocking layer. The principal cause for the subsequent Po reduction until 484 h is attributed to further decrease in ηinjection due to the appearance of certain current bypasses in addition to continuous depassivation of the NRCs in p-type AlxGa1-xN layers. According to our database on the species of vacancy-type defects acting as NRCs in GaN and AlN, which have been identified using the combination of positron annihilation and TRPL measurements, vacancy clusters comprised of a cation vacancy (VIII) and nitrogen vacancies (VN), such as VIIIVN2∼4, are the most suspicious origins of the NRCs in Mg-doped p-type AlxGa1-xN layers.
Abstract This study aimed to investigate and analyze the impurity doping characteristics in tunnel junctions (TJs) grown on core–shell structures, comprising GaInN/GaN multiple-quantum-shells (MQSs) and GaN nanowires. To this end, the impurity, structural, and electrical properties of the samples were characterized by scanning electron microscopy, scanning transmission electron microscopy, atom probe tomography (APT), nanoscale secondary ion mass spectrometry (NanoSIMS), and electroluminescence of the device which was fabricated for a prototype laser device to demonstrate an electrical operation of the MQSs layer. From the experimental results of NanoSIMS and APT, we demonstrated that the Mg-related problems in the TJ, such as the diffusion to the n ++ -GaN layer from the p + -GaN layer and formation of clusters in p + -GaN, are critical. Consequently, they cause a high operating voltage and dot-like spot emission of the light-emitting device. Based on the analysis, we suggested remedies and strategies to further improve the TJs that work well.
The fabrication of a blue m-plane GaInN light emitting diode (LED) grown on an m-plane GaN layer grown on a 3-in. patterned sapphire substrate is reported. The output power of the LED was approximately 3 mW at the wavelength of 461 nm, a driving current of 20 mA, and a forward voltage of 3.5 V. This is the first report of nonpolar or semipolar blue LEDs grown on hetero-substrates with milliwatt scale output power.
Abstract InGaN-based monolithic full-color LEDs, such as augmented reality and virtual reality, are candidates for displays with highly integrated pixels. We demonstrated a monolithic micro-LED display with green- and blue-emitting active layers separated by an n-type interlayer. The interlayer plays an important role in individually emitting green and blue light. The monolithic LED display was fabricated by mesa formation reaching the interlayer and the regrowth of the p-type layer, resulting in horizontally integrated green and blue LEDs. The display measuring 0.64 mm 2 with 20 rows and 20 columns had 40 μ m × 40 μ m pixels comprising 20 μ m × 40 μ m sub-pixels with an emitting area of 8 μ m × 23 μ m and was driven by a passive matrix circuit. Images of the monolithic micro-LED display were successfully obtained by individually controlling the green- and blue-emitting micro-LEDs. These results will enhance the commercialization of micro-LED displays.
GaInN/GaN multiple quantum shells (MQS) nanowires and p-GaN shells were embedded with n-GaN layers through tunnel junction (TJ) shells using metalorganic chemical vapor deposition (MOCVD) method. The MQS nanowires were selectively grown on n-GaN/sapphire or GaN substrates. The fabrication process of laser structures with different resonators of 600500, 750, 1000 μm, and cavity widths of 7, 12, and 17 μm were investigated with insulating layer on the sidewalls of the ridge. The structures of the fabricated devices were characterized by scanning electron microscope (SEM) and current-voltage-light output characteristics were evaluated. Two different methods for mirror formation, etching and cleavage, were developed for the laser devices. During the investigation, a superior mirror formation suffered from the difference in etching rate between GaInN and GaN, generating concaves in the MQS region. Bluegreen light emission was observed from the entire ridge surface of the MQS index-guided laser structures. A maximum current density of emission at 17.9 kA/cm2 has been confirmed in the devices. The electroluminescence and cathodoluminescence measurements demonstrated that the r-plane and c-plane at the top of the MQS are dominant at low current densities, and the m-plane emission becomes stronger as the current density increases.
Abstract We demonstrate a monolithic InGaN light-emitting diode (LED) that emits red, green, and blue (RGB) light. The proposed LED has a simple structure with stacking RGB light-emitting layers on n-GaN, wherein unnecessary layers were removed based on the desired emission color and stacking p-GaN layer. The electroluminescence characteristics of the LED indicated that the peak wavelengths at 20 mA are R : 632.9 nm, G : 519.0 nm, and B : 449.5 nm, and the external quantum efficiencies are R : 0.28%, G : 8.3%, and B : 0.84%. This structure can be manufactured using only semiconductor processes, thus rendering smaller and higher-resolution microdisplays possible.
