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By exploring spatially (μm-scale) and temporarily (ms-scale) resolved light and 8-12 μm thermal imaging analyses, we demonstrate how current crowding alternates the thermal parameters of light emitting diodes (LEDs) operating in dimming/flashing mode. For example, in AlGaInP/GaAs high-current (I ≥ 1A) large-area (≥1 mm2) LEDs, we measured the thermal time constant (2.5 ms), heat diffusion length (110 μm), current crowding length (≥75 μm), thermal diffusivity (0.08 cm2/s) of GaAs substrate, and current-dependent thermal patterns taken from the front and sidewall facet of chips. We discovered that even at I = 100 mA emitting ships are already divided by two regions with different temperatures, small area high-temperature central regions (effective volumes) with high current density and larger area lower-temperature peripheral regions with much lower current density. The experiments evidence that the simplified computer simulations of dimming mode based on mean chip temperature, mean thermal resistance, and average current density, as well as temperature- independent ABC-modeling must be regarded with skepticism. [ABSTRACT FROM AUTHOR]

We report on the radiative cooling of an indirect band gap semiconductor through its absorption of interband incoherent light and subsequent spontaneous emission of multiple longer-wavelength photons (optical down-conversion) in conditions when the energy deficit of the process is covered by the thermal energy. The 10×10×5 mm3 Si slab kept at 473 K in an evacuated up to 10-3 torr chamber was cooled by 3.8 K when pumped with light of 1.06 μm wavelength. First-principles estimates and several advantages of the down-conversion approach over possible cooling of direct band gap semiconductors through the optical upconversion and negative luminescence are discussed. [ABSTRACT FROM AUTHOR]

Silicon light emitting diode arrays made by industrial planar technology and operating at T>300 K in the double injection mode have been shown to be an efficient emitters of the infrared (IR) radiation in the 3–12 μm spectral band. We show that due to free carrier injection in an optically thin base, which makes its emissivity to increase at the wavelengths of the free carrier absorption, the devices have thermal emission output power of 2–3 mW and local power density up to 1 mW/mm2 at T=473 K. The 0.5-mm-thick 6×6 mm2 emitting pixel of an array demonstrates the power conversion efficiency of 13%, a time response of 300 μs, and an apparent temperature of the IR radiation of 400 K, which make the device practical for use in IR dynamic scene simulation techniques. [ABSTRACT FROM AUTHOR]

The results of the light and temperature micromapping in AlGaAs light emitting diodes grown by liquid phase epitaxy as double heterostructures and emitting at λ∼0.87 μm 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 found. [ABSTRACT FROM AUTHOR]

The article explains the development and the applications of the planar silicon light emitting arrays, which are used for the emission of the infrared radiation in the 3-12 [mu]m spectral band. The device is shown to be widely used for numerous IR dynamic sense simulation applications.

We report on the heat distribution inside a p[sup +]-InAsSb(Zn)/n-InAsSbP/n-InAs planar structure, emitting at 4.3 μm at 300 K. The experimental setup consists of both an infrared scanning microscope and a fiber tip as remote heat sensors (spatial resolution of some μm) operating in a time-resolved (10 μs temporal resolution) manner in the 3–5 μm spectral range. By comparing light and heat maps, we show that current crowding generates local hot regions (somewhat like heat traps) and remarkable temperature gradients (up to 3000 °C/cm) inside the emitting structure. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The InAsSbP/InAs light emitting diodes (LEDs) grown by liquid phase epitaxy and tuned at several wavelengths inside the 3–5 μm 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 μm 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. [ABSTRACT FROM AUTHOR]

The design and parameters are presented for 16-element infrared (IR, 3–12 μm) emitting arrays based on Si p+in+ structures and above-room-temperature (300 K≤T≤480 K) operated by the contact double injection. The device principle is in modulation of thermal emission beyond the fundamental absorption edge by controlling free charge carrier concentration in a base. Nearly 1.0 mW output power and 420 K apparent temperature of IR radiation could be achieved with ∼0.8% external power efficiency. This represents the longer wavelengths, higher operating temperatures, and output power from Si spontaneous emitters ever reported [ABSTRACT FROM AUTHOR]