Abstract:Phone: þ7 812 292 7922, Fax: þ7 812 297 8640Comprehensive analysis of current spreading, temperature distribution, and near-field electroluminescence (EL) of highpower flip-chip InGaN/GaN light-emitting diodes (LEDs) has been performed by combination of experimental and theoretical methods. High-resolution mapping of EL and thermal radiation was obtained by optical and infra-red (IR) microscopes. Thermal resistance of the chip was measured by forwardvoltage relaxation technique. 3D coupled electrical, thermal,… Show more
“…Design A1 has a single n-contact on one side of the device. This is known to cause current crowding effects at high current densities [24], [25]. In layout A2, the pixel group has n-metal contacts on both sides, which is typical for high LED fill-factor arrays and provides good uniformity at low current densities [3].…”
Section: Theoretical Investigation Of the Current Distributionmentioning
Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 10 6 cd/m 2 .
“…Design A1 has a single n-contact on one side of the device. This is known to cause current crowding effects at high current densities [24], [25]. In layout A2, the pixel group has n-metal contacts on both sides, which is typical for high LED fill-factor arrays and provides good uniformity at low current densities [3].…”
Section: Theoretical Investigation Of the Current Distributionmentioning
Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 10 6 cd/m 2 .
“…Sophisticated models for this have been developed recently a) and were shown to accurately describe real existing devices. [17][18][19] Here, the current density is calculated by a finite difference model following a similar ansatz to that described by Bogdanov et al 18 Sections II A and II B explain the model. In Secs.…”
Section: Current Density Distributionmentioning
confidence: 99%
“…Equation (19) was solved numerically using the fzero function of Matlab TM . A value of d ¼ 0.79 was found, yielding a resolution limit of…”
Section: E Analytical Estimate Of the Possible Resolutionmentioning
The emission area of GaN light-emitting diodes can be patterned by etch-free current aperturing methods which exploit the thin and highly resistive nature of the p-doped layer in these devices. Here, the fundamental underlying electrical and optical aspects of high-resolution current aperturing are investigated theoretically. The most critical parameter for the possible resolution is the thickness d of the p-GaN layer, but the interplay of p-GaN resistivity and electrical junction characteristics is also important. A spatial resolution of 1.59d can in principle be achieved, corresponding to about 300 nm in typical epitaxial structures. Furthermore, the emission from such a small emitter will spread by about 600 nm while propagating through the p-GaN. Both values can be reduced by reducing d.
“…Figure 1 depicts the schematic of the conduction band diagram for the as grown devices. The structure was processed as 1310 × 1310 µm 2 flip-chips, without epoxy, with design and optical properties described elsewhere [22].…”
Section: Device Structure and Experimentsmentioning
Abstract:We demonstrate a phosphor free, dichromatic GaN-based monolithic white LED with vertically stacked green and blue emitting multiple quantum wells. The optimal thickness of GaN barrier layer between green and blue quantum wells used is 8 nm. This device can be tuned over a wide range of correlated color temperature (CCT) to achieve warm white (CCT = 3600 K) to cool white (CCT = 13,000 K) emission by current modulation from 2.3 A/cm 2 to 12.9 A/cm 2 . It is also demonstrated for the first time that a color rendering index (CRI) as high as 67 can be achieved with such a dichromatic source. The observed CCT and CRI tunability is associated with the spectral power evolution due to the pumping-induced carrier redistribution.
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