Improved light extraction of GaN-based LEDs with nano-roughened p-GaN surfaces

p-GaN surfaces are nano-roughened by plasma etching to improve the optical performance of GaN-based light emitting diodes (LEDs). The nano-roughened GaN present a relaxation of stress. The light extraction of the LEDs with nano-roughened surfaces is greatly improved when compared with that of the conventional LEDs without nano-roughening. PL-mapping intensities of the nano-roughened LED epi-wafers for different roughening times present two to ten orders of enhancement. The light output powers are also higher for the nano-roughened LED devices. This improvement is attributed to that nano-roughened surfaces can provide photons multiple chances to escape from the LED surfaces.

Fabrication and optical characterization of GaN-based nanopillar light emitting diodes

InGaN/GaN-multiple-quantum-well-based light emitting diode ( LED) nanopillar arrays with a diameter of approximately 200nm and a height of 700nm are fabricated by inductively coupled plasma etching using Ni self-assembled nanodots as etching mask. In comparison to the as-grown LED sample an enhancement by a factor of four of photoluminescence ( PL) intensity is achieved after the fabrication of nanopillars, and a blue shift and a decrease of full width at half maximum of the PL peak are observed. The method of additional wet etching with different chemical solutions is used to remove the etch-induced damage. The result shows that the dilute HCl ( HCl:H2O=1:1) treatment is the most effective. The PL intensity of nanopillar LEDs after such a treatment is about 3.5 times stronger than that before treatment.

A GaN photodetector integrated structure for wavelength characterization of ultraviolet light

An interesting GaN photodetector structure, which can be used for characterizing the wavelength of incident ultraviolet light, is proposed. It is composed of two back-to-back integrated diodes, i.e. p-n and p-i-n GaN ultraviolet photodiodes with different spectral response. The wavelength of monochromatic ultraviolet light could be identified by measuring the photocurrent ratio value through a simple electronic circuit.

The performance enhancement in organic light-emitting diode using a semicrystalline composite for hole injection

A semicrystalline composite, 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) doped N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), has been fabricated and characterized. An organic light-emitting diode using such a composite in hole injection exhibits the improved performance as compared with the reference device using neat NPB in hole injection. For example, at a luminance of 2000 cd/m(2), the former device gives a current efficiency of 2.0cd/A, higher than 1.6cd/A obtained from the latter device. Furthermore, the semicrystalline composite has been shown thermally to be more stable than the neat NPB thin film, which is useful for making organic light emitting diodes with a prolonged lifetime.

Realization of extremely broadband quantum-dot superluminescent light-emitting diodes by rapid thermal-annealing process

The first demonstration, to our knowledge, of the creation of ultrabroadband superluminescent light-emitting diodes using multiple quantum-dot layer structure by rapid thermal-annealing process is reported. The device exhibits a 3 dB emission bandwidth of 146 nm centered at 984 mm with cw output power as high as 15 mW at room temperature corresponding to an extremely small coherence length of 6.6 mu m. (C) 2008 Optical Society of America.

Enhanced modulation bandwidth of a Fabry-Perot semiconductor laser subject to light injection from another Fabry-Perot laser

Variations in optical spectrum and modulation band-width of a modulated Fabry-Perot (FP) semiconductor laser subject to the external light injection from another FP Laser is investigated in this paper. Optimal wavelength matching conditions for two FP lasers are discussed. A series of experiments show that two FP lasers should have a central wavelength overlapping and a mode spacing difference of several gigahertz. Under these conditions both the magnitude and phase frequency responses can be improved significantly.

Organic light emitting diodes using magnesium doped organic acceptor as electron injection layer and silver as cathode

Organic light emitting diodes employing magnesium doped electron acceptor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (Mg: PTCDA) as electron injection layer and silver as cathode were demonstrated. As compared to Mg: Ag cathode, the combination of the Mg: PTCDA layer and silver provided enhanced electron injection into tris (8-quinolinolato) aluminium. The device with 1: 2 Mg: PTCDA and Ag showed an increase of about 12% in the maximum current efficiency, mainly due to the improved hole-electron balance, and an increase of about 28% in the maximum power efficiency, as compared to the control device using Mg: Ag cathode. The properties of Mg: PTCDA composites were studied as well.

Long-wavelength light emission from self-assembled heterojunction quantum dots

The authors report the optical characteristics of GaSb/InAs/GaAs self-assembled heterojunction quantum dots (QDs). With increasing GaSb deposition, the room temperature emission wavelength can be extended to 1.56 mu m. The photoluminescence mechanism is considered to be a type-II transition with electrons confined in InAs and holes in GaSb.(C) 2008 American Institute of Physics.