Current crowding in InAsSb light-emitting diodes

Journal of Applied Physics

Malyutenko

et al. 2008

Self Cite

The results of the light and temperature micromapping in AlGaAs light emitting diodes grown by liquid phase epitaxy as double heterostructures and emitting at ϳ 0.87 m are presented. At a driving current well above the safe operating limit ͑Ͼ300 mA͒, the nonuniform light pattern and local self-heating ͑with temperature gradient of about 950°C / cm͒ 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.

Section: Introductionmentioning

confidence: 99%

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

Journal of Applied Physics

Malyutenko

et al. 2008

Self Cite

“…The current crowding effect is well known in LEDs operating in both visible (based on InGaN [1] and AlGaInP [2]) and IR (InAsSb [3]) spectral intervals. Several investigations have been devoted to numerical simulation [4,5] and analytical modeling [1,6,7] of current spreading in LEDs.…”

mentioning

confidence: 99%

The effect of current crowding on the internal quantum efficiency of InAsSb/InAs light-emitting diodes

Kudryk

2012

Tech. Phys. Lett.

A general problem for light emitting diodes (LEDs) operating in various spectral intervals is related to the phenomenon of "crowding" of the cur rent lines in some regions of a multilayer LED struc ture, which is caused by rather high resistivities of lay ers and specific features of the LED exterior design that are determined by the need to extract radiation. The current crowding effect is well known in LEDs operating in both visible (based on InGaN [1] and AlGaInP [2]) and IR (InAsSb [3]) spectral intervals. Several investigations have been devoted to numerical simulation [4,5] and analytical modeling [1,6,7] of current spreading in LEDs. These works were aimed at improvement of current spreading in the active region of devices through optimization of the internal param eters (resistance and thickness of the substrate, con finement layers, and current spreading layers) and the geometry of contacts. It was also pointed out that cur rent crowding led to the activation of nonradiative recombination, local heating of the device structure, and a resulting decrease in the IQE of LEDs. However, no quantitative calculations of the influence of current crowding on the IQE have been performed so far.Because of the dominant role of nonradiative recombination in narrow bandgap semiconductors, the current crowding effect must be especially pro nounced in LEDs operating in the mid IR range. For this reason, we have studied mid IR LEDs based on InAsSb/InAs heterostructures, the production tech nology and main performance parameters of which are well known (see, e.g., [8,9]). This Letter presents the results of calculations of the IQE of InAsSb/InAs LEDs as a function of the injection level with allow ance for the current crowding effect.We have considered InAsSb/InAs LEDs of stan dard planar design with a round n contact of radius r 0 = 50 μm on the upper surface (Fig. 1a). The spatial distributions of current density were performed by assuming axial symmetry of the structure (LEDs have a cylindrical shape with external radius R = 300 μm). Taking into account data [8] on the internal structure of InAsSb/InAs LEDs, the proposed model takes into account the three most important layers, which are characterized by their thicknesses and resistivities: p InAs substrate (d p , ρ π ), n InAsSb active layer (d al , ρ al ), and upper n InAsSbP spreading layer (d n , ρ n ). Calculations were performed for the following numer ical values of these parameters:d n = 5 μm, ρ n = 6.2 × 10 -4 Ω cm; d p = 200 μm, ρ p = 4.1 × 10 -2 Ω cm; and d al = 2 μm. It is assumed that the active layer is characterized by a nonlinear resistance of the p-n junction, which is calculated using the diode current-voltage character istic as follows:where ϕ al is the voltage drop on the active layer, k is the Boltzmann constant, T is the absolute temperature, e is the electron charge, β is the ideality factor of the p-n junction, and j 0 is the saturation current density. All calculations were performed for β = 1, T = 300 K, and the saturation current density j 0 ...

“…In the negative luminescence mode 17 , practically all junction area remains active (see inset in Fig.3 and Fig.6, d). This is due to high junction resistance (in respect to the emitter resistance) that contributes to the current spreading across all active LED region 18 . It is very important that combining forward and reverse bias evidences unique IR LED propertythe ability to simulate hot or cold target and low observable with respect to a particular background.…”

Section: Resultsmentioning

confidence: 99%

“…More details are show in Fig.3 where the filling factor (F) of emitting surface (conditionally determined as the part of an active surface where T a values exceed 80% of the maximum) is plotted against the forward current. It is the CC that makes the emitted light to concentrate symmetrically around the top contact and "forget" a device geometry 18,19 . Longer the λ p smaller is the filling factor by decreasing from 10% (λ p = 3.4 µm) to ~1.5% (λ p = 4.2 µm).…”

Section: Resultsmentioning

confidence: 99%

“…The points of interest were the uniformity of light and heat in microscale in devices of different geometrical form and the local structure overheating that limits CW operation at room temperature. Also we wanted to see how the current crowding (CC) effect that prevents LED from being made very large area 18 depends on the emitting wavelength. However, our major goal was to measure the apparent temperature (T a ) of radiation emitted by LEDs tuned at different λ p (T a is determined as the temperature of a black body of equal power emitted in the spectral range of interest).…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Midinfrared LEDs versus thermal emitters in IR dynamic scene simulation devices

Malyutenko

2006

SPIE Proceedings

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 (T a ), thermal resistance, and self heating details were characterized at T=300 K in the microscale by calibrated infrared cameras in the 3-5 µm (light pattern) and 8-12 µm (heat pattern) bands. We show that LEDs are capable of simulating very hot (T a ≥740 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.