High external quantum efficiency (6.5%) InGaN V-defect LEDs at 600†nm on patterned sapphire substrates.

Highly efficient long-wavelength InGaN LEDs have been a research focus in nitride LEDs for their potential applications in displays and solid-state lighting. A key breakthrough has been the use of laterally injected quantum wells via naturally occurring V-defects which promote hole injection through semipolar sidewalls and help to overcome the barriers to carrier injection that plague long wavelength nitride LEDs. In this article, we study V-defect engineered LEDs on (0001) patterned sapphire substrates (PSS) and GaN on (111) Si. V-defects were formed using a 40-period InGaN/GaN superlattice and we report a packaged external quantum efficiency (EQE) of 6.5% for standard 0.1 mm2. LEDs on PSS at 600 nm. We attribute the high EQE in these LEDs to lateral injection via V-defects.

Localization Effect in Photoelectron Transport Induced by Alloy Disorder in Nitride Semiconductor Compounds.

Near-band-gap photoemission spectroscopy experiments were performed on p-GaN and p-InGaN/GaN photocathodes activated to negative electron affinity. The photoemission quantum yield of the InGaN samples with more than 5% of indium drops by more than 1 order of magnitude when the temperature is decreased while it remains constant for lower indium content. This drop is attributed to a freezing of photoelectron transport in p-InGaN due to electron localization in the fluctuating potential induced by the alloy disorder. This interpretation is supported by the disappearance at low temperature of the peak in the photoemission spectrum that corresponds to the contribution of the photoelectrons relaxed at the bottom of the InGaN conduction band.

Dependence of carrier escape lifetimes on quantum barrier thickness in InGaN/GaN multiple quantum well photodetectors.

We reported significant improvements in device speed by reducing the quantum barrier (QB) thicknesses in the InGaN/GaN multiple quantum well (MQW) photodetectors (PDs). A 3-dB bandwidth of 700 MHz was achieved with a reverse bias of -6 V. Carrier escape lifetimes due to carrier trapping in the quantum wells (QWs) were obtained from both simulation and experimental fitting, identifying carrier trapping as the major speed limiting factor in the InGaN/GaN MQW PDs.

Electrically driven, polarized, phosphor-free white semipolar (20-21) InGaN light-emitting diodes grown on semipolar bulk GaN substrate.

We demonstrate a simple method to fabricate efficient, electrically driven, polarized, and phosphor-free white semipolar (20-21) InGaN light-emitting diodes (LEDs) by adopting a top blue quantum well (QW) and a bottom yellow QW directly grown on (20-21) semipolar bulk GaN substrate. At an injection current of 20 mA, the fabricated 0.1 mm2 size regular LEDs show an output power of 0.9 mW tested on wafer without any backside roughing, a forward voltage of 3.1 V and two emission peaks located at 427 and 560 nm. A high polarization ratio of 0.40 was measured in the semipolar monolithic white LEDs, making them promising candidates for backlighting sources in liquid crystal displays (LCDs). Furthermore, a 3dB modulation bandwidth of 410 MHz in visible light communication (VLC) was obtained in the micro-size LEDs (µLEDs) with a size of 20×20 µm2 and 40×40 µm2, which could overcome the limitation of slow frequency response of yellow phosphor in commercial white LEDs combing blue LEDs and yellow phosphor.