Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN∕GaN quantum wells. Auger losses are found to be negligible in contrast to recent speculations on their importance for the experimentally observed efficiency droop. Good agreement with experimentally measured threshold losses is demonstrated. The results show no significant dependence on details of the well alloy profile.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-003310.pdf

On the importance of radiative and Auger losses in GaN-based quantum wells

Light emitting diodes (LEDs) based on In(x)Gal(1-x)N (x = 0.15-0.2)/GaN multiple-quantum wells ( MQWs) have been grown on sapphire substrates. Their wavelength emission can be tuned from blue to orange by increasing the QW thickness. This opens the way for monolithic white LEDs by combining several QWs of various thicknesses, i.e., \"colors\", inside the GaN p-n junction. This is demonstrated by the realization of white (blue + yellow) dual color LEDs. The coordinates in the CIE 1931 chromaticity diagram of the EL spectrum are (x = 0.29, y = 0.31) and correspond to a color temperature of 8000 K. The expected performances of the monolithic white LEDs are compared to hybrid technologies such as blue LEDs pumping yellow phosphors.

Monolithic White Light Emitting Diodes Based on InGaN/GaN Multiple-Quantum Wells : Semiconductors

A modified ABC model in InGaN MQW LED using compositionally step graded Alternating Barrier for efficiency improvement

In this paper, we designed and simulated a silicon carbide (SiC) technology, InGaN multiple quantum well (MQW) light-emitting diode (LED) using a compositionally step graded (CSG) InGaN barrier in the active region. The optical power, internal quantum efficiency (IQE), and carrier distribution profile in the device are theoretically studied by Sentaurus TCAD simulation. The CSG InGaN barrier LED shows substantial improvement in IQE when comparing the structures with conventional GaN barrier or InGaN barrier. This improvement is mainly due to the enhanced hole transportation/injection and modified band bending by polarization effect. The results show an excellent agreement with the experimental data. Moreover, the lattice-matched SiC substrate technology increases the radiative recombination rate in the InGaN MQW LEDs. The optical output and peak IQE obtained is 62 mW and 76.5%, respectively, for the proposed LED emitting at 450 nm wavelength at an injection current of 200 mA. This enhanced performance of the SiC technology makes it a good alternative for sapphire substrate in commercial lighting applications.

Efficiency Enhancement of InGaN MQW LED Using Compositionally Step Graded InGaN Barrier on SiC Substrate

InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with the step stage MQW structure have been investigated numerically LEDs exhibit enhanced light output power and reduced turn-on voltage with the step stage MQW Simulated results show that the improvement is mainly due to the modified band bending which is related to the polarization effect Although the good crystalline quality can reduce the nonradiative recombination, it seems that the impact is small and non-dominant in the performance improvement

Effect of Polarization Field and Nonradiative Recombination Lifetime on the Performance Improvement of Step Stage InGaN/GaN Multiple Quantum Well LEDs

In this paper, we study the characteristics of blue InGaN light-emitting diodes (LEDs) with n-AlGaN electron blocking layer (EBL) and n-AlGaN space layer (SL). The output power, internal quantum efficiency (IQE), energy band diagrams, carrier concentrations, radiative recombination and spontaneous emission rate are investigated by advanced physical model of semiconductor device (APSYS). The simulation results indicate that the LED with n-AlGaN SL shows an improvement of output power and radiative recombination than that of the LED with n-AlGaN EBL. The efficiency droop has been alleviated due to the better carrier injection and the enhancement of the overlap for the electrons and holes wave-function.

Study of Blue InGaN/GaN Light-Emitting Diodes With n-AlGaN Layer as Space Layer and Without the P-AlGaN Electron Blocking Layer

Investigation of the dual-wavelength light-emitting diodes with AlInGaN spectral adjustment layer based on the Al/In ratios

The invention discloses an LED rain and fog detector based on the Internet of Things, and a detection method and a lighting system of the LED rain and fog detector. The LED rain and fog detection method includes the following steps: S1. a double-inclined plane rain and fog collector and a microcomputer module for receiving a signal are arranged, the double-inclined plane rain and fog collector comprises a first inclined plane block and a second inclined plane block, the first inclined plane block is internally provided with an array type LED, the second inclined plane block is internally provided with an array type photoelectric receiver, and the LED and the photoelectric receiver are in one-to-one correspondence; S2. a constant current driving power supply is arranged to supply power for the array type LED; S3. the photoelectric receiver receives light from the LED, and performs signal processing on received light and then transmits to the microcomputer module to judge whether rain and fog conditions exist; and S4. the microcomputer module is provided with a rain and fog information processing module which judges the magnitude of rain and fog and measures rain and fog signal numerical values according to a received signal. Through the LED rain and fog detector based on the Internet of Things, rain and fog conditions can be known and a roadway lighting requirement can be satisfied.

LED rain and fog detector based on Internet of Things, and detection method and lighting system of the LED rain and fog detector

The invention discloses an LED multi-side lighting planer light source which comprises an LED array, an optical lens array, a condensing, diffusing and transmitting board and a transparent integral support plate. The LED array consists of multiple LEDs in arrangement. Each non-imaging secondary optical lens comprises an upper concave lens portion, a lower concave lens portion, four angles of refraction and reflection, four edges of refraction and reflection and four internal vertical sides; the four angles of the refraction and reflection of the optical lens are in rectangular arrangement, the four edges of refraction and reflection of the optical lens are arranged on four sides of the rectangle, the four internal vertical sides and the concave lens consisting of the upper concave lens portion and the lower concave lens are disposed in the middle of the rectangle, and the LEDs are disposed in the lower portion of the space formed by the four internal vertical sides of the optical lens. The LED multi-side lighting planer light source has the advantages of simple structure, small size, capability of reflecting a little light to the back, and good light intensity and uniformity within the total lighting area.

LED multi-side lighting planer light source

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