This paper reports the latest device performance of high-power blue and green Laser Diodes (LDs). The epitaxial structures of LDs including n-type, active and p-type layers were grown by metal organic chemical vapor deposition (MOCVD) on C-plane free-standing GaN substrates. And a ridge type structure and Electrodes of the n-type and p-type were formed. Front and rear mirror facets were obtained by cleavage at the m-plane surface. We optimized the epitaxial and the device structures for high efficiency, high optical output power and reliability. Every LD chip was mounted on a heat sink using a junction down method in a TO-Φ9 mm package for suppressing thermal resistance. A New developed 455 nm blue LD showed the optical output power and the voltage of 5.67 W and 3.93 V at the forward current of 3 A under Continuous Wave (CW) operation. The wall plug efficiency of the 455 nm blue LD was 48.1% at 3A. The wall plug efficiency of the high-power blue LD we developed is the highest reported so far. A new developed green LD at 525 nm showed the optical output power of 1.75 W and the wall plug efficiency of 21.2 % at the forward current of 1.9A. The optical output power, the voltage and the wall plug efficiency of a new 532 nm LD showed 1.53 W and 4.35 V, 18.5 % at the forward current of 1.9 A under CW operation. The peak wall plug efficiency of the 532 nm LD was 20 % at the optical output power of 1W.
We present latest development results of GaN based high power blue and green Laser Diodes (LDs). The epitaxial structures of LDs including n-type, active and p-type layers were grown by metal organic chemical vapor deposition (MOCVD) on C-plane free-standing GaN substrates. And a ridge type structure and Electrodes of the n-type and p-type were formed. Front and rear mirror facets were obtained by cleavage at the m-plane surface. We optimized the epitaxial and the device structures for high efficiency, high optical output power and reliability. Every LD chip was mounted on a heat sink using a junction down method in a TO-Φ9 mm package for suppressing thermal resistance. A New developed blue LD showed the optical output power and the voltage of 5.25 W and 4.03 V at the forward current of 3 A under Continuous Wave (CW) operation. The wall plug efficiency of the blue LD was 43.4% at 3A. And pure green LDs at 532 nm showed the optical output power of 1.19 W and the wall plug efficiency of 17.1 % at the forward current of 1.6A. Furthermore, 543 nm green LDs were fabricated on C-plane GaN substrates.
We report our recent improvement of watt class blue and green GaN based LDs. These LDs were grown on c-face GaN substrates by metal organic chemical deposition. The laser chip was mounted on the heat sink by the junction down method in TO-ø9 mm package for the suppression of the thermal resistance. The optical output power of 455nm blue LDs was obtained above 4.7 W at injection current of 3A. The average lifetime was estimated to be over 30,000 hours at case temperature of 65 degree C under 3A. In green LDs, 1 watt class 532 nm green LDs as same wavelength as second harmonic generation (SHG) green laser was developed and the wall plug efficiency was 12.1 %. And the longer lasing wavelength was achieved to 537 nm.
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.
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.
We measure gain spectra for commercial (Al,In)GaN laser diodes with peak gain wavelengths of 470 nm, 440 nm,
405 nm, and 375 nm, covering the spectral range accessible with electrical pumping. For this systematic study we
employ the Hakki-Paoli method, i.e. the laser diodes are electrically driven and gain is measured below threshold
current densities. The measured gain spectra are reasonable for a 2D carrier system and understandable when
we take into account homogeneous and inhomogeneous broadening. While inhomogeneous broadening is almost
negligible for the near UV laser diode, it becomes the dominant broadening mechanism for the longer wavelength
laser diodes. We compare the gain spectra with two models describing the inhomogeneous broadening. The first
model assumes a constant carrier density, while the second model assumes a constant quasi Fermi level. Both
are in agreement with the experimental gain spectra, but predict very different carrier densities. We see our
measurements as providing a set of standard gain spectra for similar laser diodes covering a wide spectral range
which can be used to develop and calibrate theoretical manybody gain simulations.
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.
We fabricated high power ultraviolet (UV) light emitting diodes (LEDs), whose emission wavelength is around 365 nm. We found that, in order to improve the external quantum efficiency (ηex) of UV LEDs, it is very important to reduce the optical self-absorption and the threading dislocation density (TDD) of epi-layers. Therefore, at first, UV LEDs epi-layers were grown on high-quality GaN templates (TDD = 2x 108/cm2) with sapphire substrates, and then the GaN templates and the sapphire substrates were removed by using laser-induced lift-off and polishing techniques. As a result, we obtained the low self-absorption and low TDD UV LEDs. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (Po), the forward voltage (Vf) and the ηex were 365 nm, 410 mW, 5.3 V, 24%, respectively. Moreover, at a forward-bias direct current of 500 mA at RT, Po, Vf and ηex were 360 mW, 5.0 V, 21%, respectively.
GaN-based laser diodes (LDs), which emit from UV to blue-green, are reviewed. For fabricating the UV LDs, we used the AlInGaN active layer instead of InGaN one. We demonstrated the UV LDs with a lasing wavelength 368nm under continuous-wave (cw) operation. Moreover, we fabricated the blue-green LDs whose lasing wavelength was 480 nm. It was investigated that the relationship between the threshold current density and the lasing wavelength. From our experiments, we successfully expanded the range of GaN-based LDs lasing wavelength, from UV (368 nm) to blue-green (480 nm). Regarding high power 405 nm-LDs, we could demonstrate the cw operated LD array devices with an output power of 1W by decreasing the thermal resistance of the LD chips.
Wide-bandgap group-ill nitride lasers, which emit from near-ultraviolet to pure-blue, are reviewed. Characteristics of 405 nm wavelength laser diodes (LDs) are discussed. Reducing threading dislocation can increase the lifetime of nitride LDs. Using epitaxial lateral overgrowth technique, the dislocation density of the order of 105 cm-2 has been obtained. The relation between the lifetime of nitride LDs and the density of dislocation are discussed. Some optical and electrical properties are very important for optical disk system such as digital versatile disk (DVD) system. In use of the DVD system, important properties of nitride LDs are discussed. Furthermore, near-ultraviolet LDs and pure-blue LDs are described. The near-ultraviolet LDs uses GaN or AlInGaN active layer instead of In GaN.
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 106/cm2, 5 X 107/cm2 and 7 X 105/cm2, 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.