Mid-infrared LEDs versus thermal emitters in IR dynamic scene simulation devices

In a radical departure from conventional thermal emitter-based dynamic IR scene simulation devices, we have tested InAsSbP/InAs LEDs grown by liquid phase epitaxy and tuned at several peak-emitting wavelengths inside the mid-IR band. Light uniformity, radiation apparent temperature (Ta), thermal resistance, and self heating details were characterized at T=300 K in the microscale by calibrated infrared cameras in the 3-5 mm (light pattern) and 8-12 μm (heat pattern) bands. We show that LEDs are capable of simulating very hot (Ta ³740 K) targets as well as cold objects and low observable with respect to a particular background. We resume that cost effective LEDs enable a platform for photonic scene projection devices able to compete with thermal microemitter MEMS technology in testing and stimulating very high-speed infrared sensors used for military and commercial applications. Proposals on how to further increase LEDs performance are given

Efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with nonuniform current spreading

We demonstrate that the efficiency droop phenomenon in multiple quantum well InGaN/GaN light-emitting diodes (LEDs) may be connected to the current crowding effect. A numerical model of internal quantum efficiency calculation is presented that takes into account nonuniform lateral carrier injection in the active region. Based on this model, we examine the effect of current crowding on the efficiency droop using comparison of simulated internal quantum efficiency of InGaN LEDs with low and high uniformity of current spreading. The results of simulations and measurements show that the devices with low uniformity of current spreading exhibit higher efficiency droop and lower roll-off current value

Bandgap dependence of current crowding effect in 3–5 μm InAsSb/InAs planar light emitting devices

Electroluminescence power profiles and 2D micropatterns have been obtained from InAsSb/InAs planar LEDs tuned at several wavelengths within the 3–5 μm band. Light confined to a small region around the top opaque contact was observed (cw mode, I > 10 mA, T = 300 K). A computer simulation showed that the reason behind the decrease of the emitting area is the current crowding that ensures non-uniform injection into the active region. The effect becomes more apparent in longer wavelength devices (emitting areas of 3.4 and 4.2 μm emitting devices are related as >10 : 1), providing direct evidence that the current crowding is affected by the bandgap energy of an active layer

Technique and setup for diagnostics of p-n junction–package thermal resistance in high-power gallium nitride LEDs

We present a setup and procedure of studying p-n junction–package thermal resistance in high-power light-emitting diodes (LEDs) from their thermal relaxation. A set of LEDs mounted on a metal-core printed circuit board (MCPCB) were studied. The contributions to the total thermal resistance from a heavy heat sink, MCPCB, heat slug and LED chip are separated

Remote temperature mapping of high-power InGaN/GaN MQW flip-chip design LEDs

We report on the study of heat 2D-distribution in InGaN LEDs with the stress made on local device overheating and temperature gradients inside the structure. The MQW InGaN/GaN/sapphire blue LEDs are designed as bottom emitting devices where light escapes the structure through the transparent GaN current spreading layer and sapphire substrate, whereas the LED structure with high-reflectivity Ni/Ag p-contact is bonded to the thermally conductive Si submount by a flip-chip method. The measurements are performed with an IR microscope operating in a time-resolved mode (3-5 μm spectral range, <20 μm spatial and 10 μs temporal resolution), while scanning a heat emission map through a transparent sapphire substrate. We show how current crowding (which is difficult to avoid) causes a local hot region near the n-contact pads and affects the performance of the device at a high injection level

The Effect of Current Crowding on the Internal Quantum Efficiency of InAsSb/InAs Light-Emitting Diodes

The effect of current crowding on the internal quantum efficiency (IQE) of InAsSb/InAs light- emitting diodes (LEDs) operating in the middle�infrared (mid�IR) range (λ = 3–5 μm) has been studied. Calculations based on a modified model of recombination coefficients show that current crowding leads to a significant decrease in the IQE of LEDs, which is especially pronounced in longer�wavelength devices (23% at λ = 3.4 μm versus 39% at λ = 4.2 μm). The obtained results indicate that the effect of current crowding should be taken into consideration as an additional nonthermal mechanism of IQE decrease in mid-IR LEDs

Temperature-dependent efficiency droop in InGaN-based light-emitting diodes induced by current crowding

Temperature-dependent internal quantum efficiency (IQE) of multiple quantum well InGaN/GaN light-emitting diodes (LEDs) has been investigated. IQE versus current relation is analysed using the modified rate equation model that takes into account the current crowding effect at different temperatures. The results of calculations are consistent with the fact that droop in IQE at higher currents originates from Auger recombination increased by current crowding. It is shown that unusual experimentally observed temperature dependence of the efficiency droop can be explained by stronger lateral nonuniformity of carrier injection at low temperatures without any assumptions about carrier delocalization from In-rich regions in quantum wells

Alloy-assisted Auger recombination in InGaN

Чисельно досліджено ефект атомної невпоряднованості на швидкість ожерекомбінації в сполуках n-InGaN типу вюрцит

The effect of current crowding on the heat and light pattern in high-power AlGaAs light emitting diodes

The results of the light and temperature micromapping in AlGaAs light emitting diodes grown by liquid phase epitaxy as double heterostructures and emitting at ��0.87 �m are presented. At a driving current well above the safe operating limit ��300 mA�, the nonuniform light pattern and local self-heating �with temperature gradient of about 950 °C/cm� followed by catastrophic degradation of a device were detected with the charge coupled device and infrared microscopes operating in a pulsed mode. These were shown to result from the current crowding effect in the active and contact areas of a device. Good agreement between the theory and experiment was foun