No abstract

A high-performance, electrically driven, single-pyramid, micro light-emitting diode (micro-LED) was demonstrated. An insulated SiO2 layer, which served as a leakage current confinement layer (LCC layer), was deposited at the lower part of the pyramid, before the deposition of the transparent conducting layer. The micro-LED with the LCC layer demonstrated a decrease in reverse leakage current by two orders of magnitude and a 190% increase in light output at 500 µA compared to a micro-LED without an LCC layer. The small leakage current enables the micro-LED to operate with an ultra-low injection current (<1 µA). The improved performance of the micro-LED is attributed to the presence of the LCC layer, which blocks the direct pathway of the leakage current via threading dislocations distributed at the lower part of pyramid and causes carriers to be injected more effectively into the active layers at the nearly defect-free apex of the pyramidal LED.

In this study, crack-free InGaN/GaN multiple quantum well (MQW) LEDs with five-pair AlN/GaN distributed Bragg reflectors (DBRs) were grown on a Si(111) substrate using a linear compositionally graded AlGaN layer to compensate for tensile stresses. DBR-based LEDs exhibited higher light efficiency and better crystalline quality than non-DBR-based LEDs. Vertical-conducting DBR-based LEDs were realized using through-hole structure. Through-holes were formed from the n-GaN layer to the Si substrate and filled with metals, which connected the n-GaN layer and the Si substrate. Insulating AlN, high-resistivity AlGaN layers, and the large band offset at the AlN/Si interface were all shorted by the metal filled into the through-holes. Compared to DBR-based LED without through-holes, DBR-based LEDs with through-holes exhibited significantly better electrical and optical properties.

Electrically driven single-pyramid InGaN/GaN micro light-emitting diode ( -LED) on silicon substrate has been fabricated and investigated. The -LED exhibits a typical p-n diode behavior with a turn-on voltage of 2.5 V and realizes an efficient electroluminescence (EL) under an ultra-small injection current (3 A). An excellent EL pattern with a high-brightness spot at apex, a hexagonal blue ring around the base of pyramid, and six bright spots at the corners of pyramid base was observed. EL wavelength centered at about 450 nm, and a slight peak shift was found as the injection current increased from 100 to 1000 A. The small magnitude of spectral shift is attributed to the growth of multiple quantum wells on semi-polar GaN pyramid side facets and its accompanied reduction of the quantum-confined Stark effect. The -LED has the promising potential for applying in micro display and electrically driven single photon emitter.

Migration characterizations of Ga and In adatoms on the dielectric surface in selective metal organic vapor phase epitaxy (MOVPE) were investigated. In the typical MOVPE environment, the selectivity of growth is preserved for GaN, and the growth rate of GaN micro-pyramids is sensitive to the period of the patterned SiO2 mask. A surface migration induced model was adopted to figure out the effective migration length of Ga adatoms on the dielectric surface. Different from the growth of GaN, the selective area growth of InGaN on the patterned template would induce the deposition of InGaN polycrystalline particles on the patterned SiO2 mask with a long period. It was demonstrated with a scanning electron microscope and energy dispersive spectroscopy that the In adatoms exhibit a shorter migration length on the dielectric surface.