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 .

We investigated the optical, spectral and thermal characteristics of GaN-based blue vertical light emitting diodes (VLEDs) on graphite substrate in comparison with conventional lateral LEDs (LLEDs) on sapphire substrate with a mesa size of 1 × 1 mm 2 . For fabricated VLEDs and LLEDs, the temperature-dependent optical and spectral characteristics were measured in the temperature range of 288-378 K and the junction temperatures (T j ) were experimentally determined by the forward voltage method. From these results, the improved optical property and high thermal stability were achieved by the VLED structure on graphite substrate. At 350 mA, the optical output power of the VLED on graphite substrate was improved by 23% compared to the LLED on sapphire substrate at the temperature of 298 K. Also, the VLED on graphite substrate exhibited lower junction temperature and thermal resistance than those of the LLED on sapphire substrate.