We report the InGaN/GaN multiple quantum well vertical light-emitting diodes (VLEDs) operating at λ ∼ 450 nm by the use of laser lift-off and copper electroplating processes. The thermal characteristics of fabricated VLEDs are measured and analyzed in terms of the junction temperature (T j ) using the forward voltage method, which allows us to estimate the thermal resistance (R th ). Between 298 and 378 K, the characteristic temperature is measured to be about 903 K at 350 mA. The far-field patterns of the VLED have a uniform and good near-Lambertian emission. The T j and R th values are also confirmed by the emission peak wavelength shift method. The use of electroplated copper with a high thermal conductivity instead of a sapphire substrate provides much better heat dissipation capability. For a 1 × 1 mm 2 VLED, the low T j value of 305.8 K is obtained with an output power of 191 mW at an injection current of 350 mA at 298 K, exhibiting R th = 7.98 K W −1 .

In this study, we have fabricated the high-power GaNbased vertical light-emitting diodes (VLEDs) by exploiting a thermally stable nano-scaled Ni-Ag-Ni-Au mirror. After being treated at 600 C for 1 min in air ambient, the nano-scaled Ni-Ag-Ni-Au (5/2000/1000/2000 Å) mirror shows the specific contact resistance of cm and its reflectivity has increased from 89.5% to 93.0%. The increment in the reflectivity is due to the diffusion of Ni contact layer into Ag layer. Moreover, the reflectivity of the mirror has hardly deteriorated even after the wafer was thermally bonded with graphite substrate at 320 C for 5 min, meaning that the proposed mirror is thermally reliable. The light output power of the nano-scaled VLED (Chip size: 1 1 mm ) with thermal treatment at 600 C for 1 min is enhanced by 8% as compared to one without thermal treatment at an injection current of 350 mA. To our knowledge, our nano-scaled mirror has the highest reflectivity among other Ag-based multilayered reflectors, and thus it is a promising candidate for high-performance VLED. Index Terms-GaN, light-emitting diodes (LEDs), light output power, thermally stable mirror, wafer bonding.

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We report the device characteristics of InGaN/GaN blue vertical light emitting diodes (VLEDs) by additional KOH surface roughening process through the wafer-level fabrication/ test, and their simulation analysis in terms of electrical and optical properties. The influence of additional KOH etching time on the evolution of the rough surface and the device performance of VLEDs was investigated. With applying the additional surface roughening, the average operating voltage was gradually increased. In contrast, the average optical output power was increased upto a certain roughening time, but then it decreased again. As a whole, by applying an adequate additional roughening process, the optical power was improved without noticeable increase in the operation voltage. From the simulated current density and light extraction efficiency results, these device behaviours were well explained by the current crowding and bulk absorption effects.

A new tensile strained InGaAs/InGaAlAs quantum well structure in the 1.3 µm wavelength region is proposed for high temperature characteristics via quantum well band structure and optical gain calculations. To obtain such features, a tensile-strained InGaAs/InGaAlAs quantum well structure, which emits light dominated by TM polarization, is considered. This proposed structure has very high temperature characteristics (T 0 > 130 K) due to its high density of state at the first transition edge. This results clearly show the potential of tensile strained quantum well structure usage for the high temperature operation of quantum well semiconductor lasers.

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