Performance Of InGaN Light-emitting Diodes Research Articles

Effects of high-dose 80 MeV proton irradiation on the electroluminescent and electrical performance of InGaN light-emitting diodes

The paper reports on the degradation of InGaN/GaN Blue LED submitted to proton irradiation at 80 MeV and various fluences (4×1013 p cm−2 and 1×1014 p cm−2). After irradiation, we found a decrease in light output power and the external quantum efficiency with fluence. Photoluminescence (PL) measurements exhibited that the peak position at 400, 447 and 568 nm remained unchanged, only the peak intensity decreased. The intensity of the blue emission reduced by 75%, indicating that the active region degraded seriously; the intensity from In x Ga1-x N (x = 0.11) reduced more than two times in comparison with the blue emission, implying that proton irradiation affected In x Ga1-x N more seriously than InGaN/GaN MQWs. The degradation of LED is ascribed to the increase in the defect-related Shockley–Read–Hall recombination after 80 MeV proton irradiation with higher fluence.

Performance improvement of InGaN LEDs by using strain compensated last quantum barrier and electron blocking layer

The influence of u-AlGaN/InGaN superlattices (SLs) last quantum barrier (LQB) and p-AlGaN/InGaN SLs electron blocking layer (EBL) on the performance of InGaN light-emitting diodes (LEDs) are analyzed experimentally and theoretically. Research results indicated that LED C with u-AlGaN/InGaN SLs LQB and p-AlGaN/InGaN SLs EBL exhibit the highest output power among the three groups of LED samples. At 200 mA, the output power of LED C is enhanced by 27.5% as compared with that of reference LED A with u-GaN LQB and p-AlGaN/GaN SLs EBL. The efficiency droop of LED C has also been suppressed effectively. At 200 mA, the efficiency droop of LED C was 28.5%, which was smaller than that of LED A 34%. By analyzing the distribution of electron/hole concentration in multiple quantum wells, it is indicated that the leakage of electrons from the active layer can be effectively reduced and the injection efficiency of holes into the active layer can be dramatically enhanced by using strain compensated AlGaN/InGaN SLs LQB and EBL. The reason is that the potential energy barriers for electrons and holes could be effectively regulated by using the strain compensated LQB and EBL, which is consistent with simulation results of energy band diagram.

Efficiency enhancement of an InGaN light-emitting diode with a u-InGaN/AlInGaN superlattice last quantum barrier

In this study, a new design on last quantum barrier (LQB) is investigated numerically with the purpose of improving the optical performance of InGaN light-emitting diodes (LEDs). Through the analysis of the energy band diagrams, electrostatic fields, carrier concentrations, carrier current densities, and radiative recombination rates, we have got the simulation results that the proposed undoped-InGaN/AlInGaN superlattice (SL) LQB can significantly improve the output power and internal quantum efficiency, which is mainly attributed to the successful improvement in hole injection efficiency and suppression of electron current leakage. Moreover, the efficiency droop of the LEDs is improved slightly by using u-InGaN/AlInGaN SL as last barrier.

Effect of n-type barrier doping on steady and dynamic performance of InGaN light-emitting diodes

The steady and dynamic properties are comparatively investigated for the n-doped and non-doped InGaN LEDs. The simulated results show that the n-doped LED exhibits the superior luminescence and modulation performance, which is mainly attributed to the higher carrier radiative rate of n-doped LED. The results can explain the reported experimental results perfectly.

Enhanced performance of InGaN light-emitting diodes with InGaN and composition-graded InGaN interlayers

The effects of InGaN light-emitting diodes (LEDs) with InGaN and composition-graded InGaN interlayers in the space of multiple quantum wells and electron blocking layer are studied numerically. The electrostatic field, energy band diagrams, carrier concentrations, light–current–voltage performances, and internal quantum efficiency (IQE) are investigated. Simulation results show that the light output power and IQE are both largely improved over the conventional LED structure due to the improvement in hole injection efficiency and electron blocking capability, especially for the LED with composition-graded InGaN interlayer.

Performance of InGaN Light-Emitting Diodes Fabricated on Patterned Sapphire Substrates with Modified Top-Tip Cone Shapes

InGaN light-emitting diodes (LEDs) were fabricated on cone-shaped patterned sapphire substrates (PSSs) by using low-pressure metalorganic chemical vapor deposition. To enhance the crystal quality of the GaN epilayer and the optoelectronic performance of the LED device, the top-tip cone shapes of the PSSs were further modified using wet etching. Through the wet etching treatment, some dry-etched induced damage on the substrate surface formed in the PSS fabrication process can be removed to achieve a high epilayer quality. In comparison to the LEDs prepared on the conventional sapphire substrate (CSS) and cone-shaped PSS without wet etching, the LED grown on the cone-shaped PSS by performing wet etching for 3 min exhibited 55% and 10% improvements in the light output power (at 350 mA), respectively. This implies that the modification of cone-shaped PSSs possesses high potential for LED applications.

Improved performance of InGaN light-emitting diodes with a novel sawtooth-shaped electron blocking layer

A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes (LEDs). The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the electron leakage, and the internal quantum efficiency are systematically studied. The simulation results show that the LED with a sawtooth-shaped electron blocking layer possesses higher output power and a smaller efficiency droop than the LED with a conventional AlGaN electron blocking layer, which is because the electron confinement is enhanced and the hole injection efficiency is improved by the appropriately modified electron blocking layer energy band.

High performance of InGaN light-emitting diodes by air-gap/GaN distributed Bragg reflectors

The effect of air-gap/GaN DBR structure, fabricated by selective lateral wet-etching, on InGaN light-emitting diodes (LEDs) is investigated. The air-gap/GaN DBR structures in LED acts as a light reflector, and thereby improve the light output power due to the redirection of light into escape cones on both front and back sides of the LED. At an injection current of 20 mA, the enhancement in the radiometric power as high as 1.91 times as compared to a conventional LED having no DBR structure and a far-field angle as low as 128.2° are realized with air-gap/GaN DBR structures.

Improving the optical performance of InGaN light-emitting diodes by altering light reflection and refraction with triangular air prism arrays

The effect of triangular air prism (TAP) arrays with different distance-to-width (d/w) ratios on the enhancement of light extraction efficiency (LEE) of InGaN light-emitting diodes (LEDs) is investigated. The TAP arrays embedded at the sapphire/GaN interface act as light reflectors and refractors, and thereby improve the light output power due to the redirection of light into escape cones on both the front and back sides of the LED. Enhancement in radiometric power as high as 117% and far-field angle as low as 129° are realized with a compact arrangement of TAP arrays compared with that of a conventional LED made without TAP arrays under an injection current of 20 mA.

Effects of high-dose 40MeV proton irradiation on the electroluminescent and electrical performance of InGaN light-emitting diodes

InGaN multi-quantum-well light-emitting diodes (LEDs) in the form of unpackaged die with emission wavelengths from 410 to 525nm were irradiated with 40MeV protons to doses of 5×109–5×1010cm−2. The highest dose is equivalent to more than 100 years in low-earth orbit. The projected range of these protons is >50μm in GaN and thus they traverse the entire active region. The electroluminescent intensity from the LEDs decreased by only 15%–25% even for the highest doses and the reverse breakdown voltage increased by 1–2V from their control values of ∼21–29V. The percentage change in breakdown voltage and electroluminescence intensity was independent of the initial emission wavelength over the range investigated, within experimental error. The GaN LEDs exhibit extremely good stability to these high-energy proton irradiations with no measurable change in contact resistance or contact morphology.