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 (η<sub>L</sub>) of 161 Lm/W with the high luminous flux (φ<sub>v</sub>) of 9.89 Lm at a forward-
current of 20 mA. Used blue LED had a high output power (φ<sub>e</sub>) of 42.2 mW and high external quantum efficiency (η<sub>ex</sub>)
of 75.5%. The second one is the luminous-efficiency-maximized white-LED with a low forward-bias voltage (V<sub>f</sub>) of
2.80 V, which is almost equal to the theoretical limit. η<sub>L</sub> 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.
The first-order AlInGaN 405 nm distributed feed-back (DFB) laser diodes were grown on the low dislocation freestanding
GaN substrates by a metal organic chemical vapor deposition method. The first-order diffractive grating whose
period was 80 nm was formed into an n-type cladding layer. The fine tooth shape grating was obtained by the EB
lithography and the dry etching. No additional threading dislocation could be found at the regrowth interface. As a result,
we succeeded in demonstrating the first-order AlInGaN based 405 nm DFB laser diodes under cw operation. The
threshold current and the slope efficiency were 22 mA and 1.44 W/A under continuous wave operation at 25 °C,
respectively. The single longitudinal mode emission was maintained up to an output power of 60 mW. The fundamental
transverse mode operation with a single longitudinal mode was observed in the temperature range from 15 °C to 85 °C at
an output power of 30 mW. The lifetime was estimated to be 4000 h by the lifetime test which was carried out under the
condition of a constant output power of 30mW at 25 °C for 1000 h. The single longitudinal mode emission was
maintained for the life tested DFB laser diodes.
High-power pure blue laser diodes (LDs) are expected to be adopted to the light sources for full color laser display
systems. We have succeeded in fabricating high-power blue (445nm) LDs with an output power of 500mW. The typical
operating current, voltage and wall-plug efficiency of these LDs were 480mW, 4.8V and 21.7%, respectively. The
lifetime of these LDs was estimated to be over 10,000 hours under continuous-wave operation. Moreover, we succeeded
in fabricating the high-luminance white light source by combining the high-power blue LD, optical fiber, and phosphor.
In this paper, we report recent progress and future prospects of the high-power GaN-based blue LDs and the new
concept of high-luminance white light source.
Since the first demonstration of a pulsed InGaN laser diodes (LDs) grown on sapphire substrate in 1995, we have been developing longer lifetime and higher optical output power LDs in the 400 - 410 nm wavelength range. Moreover, we have already succeeded in the expansion of the lasing wavelength range from ultraviolet (UV) to blue-green. In this paper, we reported the recent progress of high-power and wide wavelength range GaN-based LDs with an optical output power of 20 mW single mode (375nm), 160 mW single mode (405nm), 200 mW multi mode (405nm), 50 mW single mode (445nm), 300 mW multi mode (445nm), and 20 mW single mode (473nm).
Nine years has passed since the initial development of GaN-based violet laser diodes (LDs) in the 405 nm wavelength range in 1995. Starting with next-generation high-density optical discs, the commercial use of violet LDs has been adopted in many new fields, such as biomedical, reprographic, and exposure fields. Recently, lasing wavelength has broadened to cover from the ultraviolet (UV) to blue-green regions, which enabled other new applications. In this paper, the current status of GaN-based LDs from the UV to blue-green regions is reported.
Three kinds of substrates were used for violet InGaN multi- quantum-well/GaN/AlGaN separate-confinement-heterostructure laser diodes (LDs). One of substrates is epitaxially laterally overgrown GaN (ELOG) substrate. Another is `free- standing GaN' substrate. In order to obtain it, thick GaN was grown on `ELOG', and then, sapphire and `ELOG' were removed. Third one is `ELOG grown on thick GaN' substrate. The threading dislocation densities of `ELOG', `free- standing GaN' and `ELOG grown on thick GaN' were 1 X 10<SUP>6</SUP>/cm<SUP>2</SUP>, 5 X 10<SUP>7</SUP>/cm<SUP>2</SUP> and 7 X 10<SUP>5</SUP>/cm<SUP>2</SUP>, respectively. LDs were fabricated with the structure of epi side up. The estimated lifetime of LD grown on `ELOG grown on thick GaN' was 15000 h under condition of continuous-wave operation, case temperature of 60 degree(s)C and output power of 30 mW.