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

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

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

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

Room-temperature InAsSbP/InAs light emitting diodes by liquid phase epitaxy for midinfrared (3–5 mkm) dynamic scene projection

The InAsSbP/InAs light emitting diodes LEDs grown by liquid phase epitaxy and tuned at several wavelengths inside the 3–5 mkm band were tested. Light pattern, radiation apparent temperature Ta, thermal resistance, and self-heating details were characterized at T=300 K in microscale by calibrated infrared cameras operating in the 3–5 and 8–12 mkm bands. The authors show that LEDs dynamically simulate very hot Ta=750 K targets as well as cold objects and low observable. They resume that low cost LEDs enable a platform for photonic scene projection devices able to compete with thermal microemitter technology. Proposals on how to further increase LEDs performance are given