We fabricated the high efficiency white LEDs. The white LEDs, the yellow YAG-phosphors-coated small-size (290µm × 500µm) blue LED, designed for minimizing forward voltage. At a forward current of 20mA, the luminous flux, the forward voltage (Vf), the correlated color temperature (Tcp), the luminous efficiency, and the wall-plug efficiency (WPE) are 9.5lm, 2.8V, 5193K, 169Lm/W, and 50.8%, respectively. The high-power white LEDs were fabricated from the larger-size (1mm × 1mm) blue LED chips with the output power of 651mW at 350mA. Flux, Vf, Tcp, luminous efficiency, and WPE of the high-power white LED are 145Lm, 3.09V, 4988K, 134Lm/W, and 39.5%, respectively, at 350mA. This power white LEDs showed total flux of 361Lm at 1A. Moreover, we succeeded in developing high-power and high-efficiency blue laser diodes (LDs) with an emission wavelength at 445nm range by using GaN-based materials. This achievement leads to the full-color laser display applications. We fabricated multi-transverse mode LDs by a single emitter, and adopting φ9mm packages for the reduction of the thermal resistance. The typical optical-output power, voltage and wall-plug efficiency of the LDs at forward current of 1.0A at a temperature of 25ºC was 1.17W, 4.81V and 24.3%, respectively. The catastrophic optical damage at the facets of these LDs did not appear up to 3W in the optical output power. The estimated lifetime of the LDs at a temperature of 25ºC under continuous-wave operation 1.0A in automatic current control condition was over 30,000 hours.
We fabricated two types of high luminous efficiency white light emitting diodes (LEDs). The first one is the white
LED, which had a high luminous efficiency (ηL) of 161 Lm/W with the high luminous flux (φv) of 9.89 Lm at a forward-
current of 20 mA. Used blue LED had a high output power (φe) of 42.2 mW and high external quantum efficiency (ηex)
of 75.5%. The second one is the luminous-efficiency-maximized white-LED with a low forward-bias voltage (Vf) of
2.80 V, which is almost equal to the theoretical limit. ηL and wall-plug efficiency (WPE) were 169 Lm/W and 50.8%,
respectively, at 20 mA. They were approximately twice higher than those of a tri-phosphor fluorescent lamp (90 Lm/W
and 25%). Moreover, we succeeded in fabricating longer wavelength laser diodes (LDs) with an emission wavelength of
488 nm under CW current condition by optimizing the growth conditions and structure of LDs. To our knowledge, this
wavelength is the longest for under CW current condition in GaN-based LDs.