Preface

Mroziewicz, B.; Bugajski, M.; Nakwaski, W.

doi:10.1016/b978-0-444-98737-2.50003-4

Cited by 25 publications

(49 citation statements)

References 0 publications

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“…7. The measured wavelength separation between neighbouring peaks is around 8 nm that well agrees with the separation of the allowed modes assuming the epitaxial thickness as the cavity length (∆λ = λ 2 /2n eff L: n eff effective refractive index, L cavity length) [7]. The thermal resistance of the vertical LED is measured to be 48 K/W and far smaller than 240 K/W of the conventional p-side up LED on sapphire.…”

Section: Device Characteristicsmentioning

confidence: 74%

Vertical InGaN‐based blue light emitting diode with plated metal base fabricated using laser lift‐off technique

Ueda

Ishida

Tamura

et al. 2003

phys. stat. sol. (c)

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A vertical InGaN-based blue light emitting diode (LED) with a reflective metal electrode and thick gold plated base free from insulating sapphire is demonstrated. A 50 µm-thick gold plated layer on a highly reflective platinum p-side ohmic contact is formed on the InGaN-based LED epi-structure, followed by irradiation with high power ultra-violet pulsed laser from the backside of the original sapphire substrate. The laser processing, so called laser lift-off technique, enables the separation of sapphire by decomposition of interfacial GaN layer. No transparent electrode is necessary for the LED because the current can spread well through the highly conductive n-GaN layer so that uniform blue light is emitted through the n-GaN layer. The electroluminescence (EL) spectra show small multi peaks due to the resonance within the formed vertical cavity. In addition, the measured thermal resistance of the vertical LED is smaller than that of the conventional LED on poor heat-conductive sapphire. The vertical LED would increase the brightness together with smaller chip size and lower series resistance. This would be advantageous espacially for high power and highly efficient LEDs applicable to future solid state lighting. 1 Introduction GaN-based visible light emitting diodes (LEDs) have been widely used for various applications such as indicators, signals and large displays. High power and highly efficient white LEDs excited by the GaN-based LEDs would enable future solid state lighting, as well. So far, sapphire has been the most commonly used substrate for the LED fabrication. However, sapphire is a poor heatconductive material and the LED on it needs to have both electrodes on the same side due to its insulating nature resulting in large chip size and potentially higher series resistance. Thus the use of sapphire limits further improvement of the device performances, even though the epitaxial layer of the best quality has been obtained on the cost-effective substrate. In order to solve such disadvantages keeping the use of sapphire as a substrate, removal of GaN or InGaN-based device layers by using high power ultra-violet pulsed laser, so-called laser lift-off technique, has been demonstrated [1,2]. So far, blue LEDs on silicon substrates fabricated by using laser lift-off process has been reported [3]. Attaching better heat sink than silicon with better reflectivity on the separated LED structure would enable higher power output of the LED with better reliability. This paper reports a new vertical InGaN-based LED with a reflective metal electrode and thick gold plated base free from insulating sapphire. The LED structure grown on a sapphire substrate is separated using the laser lift-off technique after the formation of the electrode and plated metal base. This vertical LED emits uniform blue light through highly conductive n-GaN layer with smaller thermal resistance.

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Section: Device Characteristicsmentioning

confidence: 74%

Vertical InGaN‐based blue light emitting diode with plated metal base fabricated using laser lift‐off technique

Ueda

Ishida

Tamura

et al. 2003

phys. stat. sol. (c)

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“…There are a number of factors which affect the threshold in optical pumped laser structures. The higher threshold of laser 2 can be explained by a smaller confinement factor defined as the overlap of the optical mode with the active region [9]. In addition, the smaller contrast of the refractive indices between the waveguide (6% instead of 4% of aluminum) and cladding layer (12%) increases the threshold.…”

Section: Resultsmentioning

confidence: 99%

Optically Pumped Laser Action on Nitride Based Separate Confinement Heterostructures Grown along the (11¯20) Crystallographic Direction

et al. 2007

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The intention of this work is to discuss and report on our research on nonpolar laser structures grown on bulk GaN crystal substrates along the (1120) nonpolar direction. The main advantages of such nonpolar structures are related to the elimination of the built-in electric fields present in commonly used systems grown along the polar (0001) axis of nitride crystals. We demonstrated the optically pumped laser action on separate confinement heterostructures. Laser action is clearly shown by spontaneous emission saturation, abrupt line narrowing, and strong transversal electric polarization of output light. The lasing threshold was reached at an excitation power density of 260 kW/cm 2 for a 700 µm long cavity (at room temperature).

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“…The threshold of laser operation is obtained if the gain in the resonator compensates for the overall losses, i.e., the propagation losses and the apparent losses due to the extraction of light [1][2][3][4]. Figure 1.1 shows the energy band structure with nearly free carrier approximation [2].…”

Section: Energy Band Theorymentioning

confidence: 99%

“…Only if the optical gain is greater than the threshold gain g th , the laser operation can be established. The threshold gain g th is calculated and expressed as [2,3] …”

Section: Principle Of Semiconductor Lasersmentioning

confidence: 99%