Semiconductor lasers with emission in the range 790 - 880 nm are in use for a variety of application resulting in
different laser designs to fulfill requirements in output power, operation temperature and lifetimes. The output power is
limited by self heating and catastrophic optical mirror damage at the laser facet (COMD). Now we present data on bars
fabricated with our new facet technology, which enables us to double the maximum facet load. We present q-cw laser
bar with 80% fill factor with increased power level to 350W in long term operation at 200μs and 100Hz. The COMD
limit of the bar is as high as 680W. Using Quantel's optimized packaging stacks with 11 bars of 5mm widths are tested
at up to 120A resulting over 66% power conversion efficiency at 1600W output power. Laser bars for continuous wave
operation like 50% fill factor bars had an COMD limit of approx. 250W with conventional facet technology, the value is
equivalent to 10W per 200μm emitter (conditions: 200μs). The new facet technology pushes the facet stability to
24W/emitter. The new process and an improved design enable us to shift continuous wave operation at 808nm from
100W to 150W/bar with lifetimes of several thousand hours at 30°C using DILAS mounting technology. Higher power
is possible depending on lifetime requirements. The power conversion efficiency of the improved devices is as high as
62% at 200W cw. The next limitation of 8xxnm lasers is high temperature operation: Values of 60-80°C are common for
consumer applications of single emitters. Therefore Osram developed a new epitaxial design which reduced the
generation of bulk defects. The corresponding Osram single emitters operate at junction temperatures up to 95°C, a value
which corresponds to 80°C heat sink temperature for lasers soldered on C-mount or 65°C case temperature for lasers
mounted in TO can. Current densities of the single emitter broad area lasers are as high as 1.4kA/cm2 at 850nm emission
We report temperature tuning of pulsed operated InGaN LDs (5×500μm stripe,
grown on low-dislocation, high-pressure grown GaN substrates). The devices
are characterized by a rather weak temperature dependence of the threshold
current. A very broad temperature tuning range of 16nm was obtained with
increase of operation temperature by almost 200K. We were able to tune the
diode from the initial wavelength of 415nm at room temperature up to 431nm
at 201°C. After thermally cycling the device no substantial degradation was
noticed. We observed multimode emission and mode hopping with temperature
increase. At 201°C the laser's threshold current doubled and the slope efficiency
of the L-I curve dropped by 35%. These results demonstrate the potential
usage of temperature tuning of nitride-based-LDs for the atomic spectroscopy-related applications.
Metalorganic vapor phase epitaxy (MOVPE) and plasma assisted molecular beam epitaxy (MBE) were used as alternative techniques to fabricate similar group-III-nitride laser structures. Utilization of high-pressure-grown GaN substrates resulted in reduction of threading dislocation density down to 105 cm-2. Light amplification features of the measured structures were evaluated by means of the variable stripe length method. Maximum peak modal gain values of 180 cm-1 for the MOVPE-grown sample and 315 cm-1 for the MBE-grown one were reached at corresponding pump power of 464 kWcm-2. Temperature-dependent photoluminescence measurements yielded activation energies of 41 meV nad 22 meV for MOVPE- and MBE-grown samples, respectively. Saturation lengths of 350 &mgr;m and 250 &mgr;m determined for MOVPE and MBE structures indicate reduced rate of nonradiative recombination compared to heteroepitaxy on foreign substrates. Differences in nonradiative recombination processes between the investigated structures lead to deviations in threshold for stimulated emission in favor of the MBE-grown sample.
We fabricated wide-stripe laser diodes operating between 380 and 430 nm. The threshold current density for 380 and 430 nm devices (6-7 kA/cm2) was only slightly higher than for our main stream 415 nm devices (4-6 kA/cm2). Thanks to the use of high-pressure-grown low-dislocation-density substrates we succeeded in demonstration of high power optical emission both under CW and pulse operation. For the device emitting at 415 nm we were able to demonstrate 200 mW of CW optical power (20 μm wide device) and 2.7 W under pulse current operation (peak power, 50 μm device). The main obstacle for achieving CW operation of 50 μm device was to remove the excess of heat from laser chip-diamond submount assembly.
We demonstrate the operation of wide-stripe InGaN laser diodes grown on bulk gallium nitride substrates obtained by high-pressure synthesis. The use of almost dislocation-free substrates resulted in very low defect densities of obtained laser structures - typically in the range of 105cm-2. We tested 3 types of devices of the dimensions: 20μmx500μm, 20μmx1000μm and 50μmx500μm. All three types of lasers showed good properties during pulse current experiments, exhibiting threshold currents of 400, 850 and 950 mA, respectively. The lasing wavelength varied between 405 and 420 nm, depending on the particular device. After p-down mounting on diamond heatspreaders, the first two types of lasers showed CW operation with a total output power reaching 200 mW. These devices, after optimization, offer good prognostics for reaching an optical power in the 1 W range needed for the applications in large area displays.
High pressure grown GaN bulk crystals, because of their low defect density, are atractive for the use as substrates for blue-violet laser diode fabrication. These laser diodes are characterized by a low density of dislocations (8×104-1×105 cm-2) and thus they possibly have the best crystalline quality ever reported for this type of nitride devices. Previously, we demonstrated that these lasers are able to emit a very high optical power under pulse operation. In the present paper we will demonstrate the details of their room temperature CW operation, giving good prognostics for the further development of these devices. Preliminary estimation of the internal losses indicated a very low internal absorption in the range of 5 cm-1. The characterization of the aged devices did not reveal any dark lines or facet degradation. A correlation between the device lifetime and p-type layers growth methods will be suggested here.
High-power laser diodes emitting in the violet - UV region are needed for many applications related to data storage, full color laser projectors, pollution screening etc. This type of device is difficult to fabricate by using the presently available technology of epitaxial growth which employs the lateral overgrowth scheme to reduce the dislocation density in the active layer of the device. This paper presents a new generation of wide stripe laser diodes, which structures were coherently grown on bulk, nearly defect free GaN substrates. Thanks to a low and homogeneously distributed dislocation density (3×105cm-3), these devices are able to emit a very large optical power in excess of 2.5 W with a slope efficiency per facet of around 0.3 W/A and threshold current densities of 5-10 kA/cm2. The use of wide 15 μm stripe lowers the optical power density on the mirrors, and helps avoiding their optical damage. We believe that these devices clearly show the potential of homoepitaxy for high-power lasers applications.