Electrical, spectral and optical performance of yellow–green and amber micro-pixelated InGaN light-emitting diodes

Abstract

Micro-pixelated InGaN LED arrays operating at 560 and 600 nm, respectively, are demonstrated for what the authors believe to be the first time. Such devices offer applications in areas including bioinstrumentation, visible light communications and optoelectronic tweezers. The devices reported are based on new epitaxial structures, retaining conventional (0 0 0 1) orientation, but incorporating electron reservoir layers which enhance the efficiency of radiative combination in the active regions. A measured output optical power density up to 8 W cm −2 (4.4 W cm −2 ) has been achieved from a representative pixel of the yellow-green (amber) LED array, substantially higher than that from conventional broad-area reference LEDs fabricated from the same wafer material. Furthermore, these micro-LEDs can sustain a high current density, up to 4.5 kA cm −2 , before thermal rollover. A significant blueshift of the emission wavelength with increasing injection current is observed, however. This blueshift saturates at 45 nm (50 nm) for the yellow-green (amber) LED array, and numerical simulations have been used to gain insight into the responsible mechanisms in this microstructured format of device. In the relatively low-current-density regime (<3.5 kA cm −2 ) the blueshift is attributable to both the screening of the piezoelectric field by the injected carriers and the band-filling effect, whereas in the high-current regime, it is mainly due to band-filling. Further development of the epitaxial wafer material is expected to improve the current-dependent spectral stability.

Directly color-tunable smart display based on a CMOS-controlled micro-LED array

“…1] is observed as the injection current is increased. Both the screening of the quantum-confined Stark effect in polar QWs and the band-filling effect can lead to this blueshift, and a detailed investigation of the relevant physics along with the numerical stimulation results has been reported [1]. Fig.…”

“…To implement the micro-display system, we fabricate a dedicated micro-pixel LED array from this InGaN structure, interface it to a CMOS driver array and show direct display performance and color tuning under the CMOS control. Our InGaN material contains high (0.4) indium mole-fraction quantum wells, and we have recently reported the physics of color tuning in this material [1]. Further measurement shows that the modulation bandwidth of these integrated micro-LED/CMOS tunable pixels reaches 100 MHz, thus also providing a wavelength-agile source for high speed visible light communications.…”

“…The µLED device used for the micro-display demonstration was fabricated by using a similar process, and with similar high-In quantum well material, to that previously reported [1]. It consists of a 16×16 array of individually addressable micro-disk LED pixels with a diameter of 72 µm on a 100 µm center-to-center pitch.…”

Spectral competition of chirped dual-wavelength emission in monolithic InGaN multiple-quantum well light-emitting diodes

“…15 Gong et al experimentally and numerically demonstrated the electrical, spectral, and optical performances of yellow-green and amber micro-pixelated InGaN LEDs to gain insight into the responsible mechanisms of dualwavelength emission. [16][17][18] Based on these researches, the properties of light-emission and dynamics of carrier transportation in the dual-wavelength InGaN/GaN MQW LEDs were further clarified. In addition to the important issues of color rendering index (CRI), carrier localization due to the indium-rich nanostructures, and difficulty in growth of high indium-content alloys, there are some other significant problems which need to be solved toward the commercial realization of dual-wavelength monolithic InGaN MQW LEDs.…”

“…26 Moreover, a broad-band LED with a shallow first well, which plays the role of prestrain layer or electron reservoir layer, is also explored and compared. [16][17][18]24 For the exploration of spectral competition between the green and violet emissions, the spontaneous emission rates as a function of wavelength for the four LEDs under study at 20, 100, 180, and 260 mA are depicted in Fig. 2.…”