Improvement of thermal stability of green quantum dot light emitting diodes (QD-LEDs) was demonstrated by using composition-gradient thick-shell CdSe@ZnS/ZnS quantum dots (QDs). The electroluminescence intensity only decreased 3% even when the operation temperature was elevated to 110 °C. The current efficiency roll-off effect was improved nearly 200% under higher current density. Thick-shell QDs with low defective structure could effectively prevent the electron-hole pairs from nonradiative Auger recombination and avoid the thermal-stress-induced expansion at higher temperatures and driving current. The maximum current efficiency of the thick-shell-device is 10.3 cd/A, which is much higher than 1.57 cd/A for the conventional thin-shell-device.
High-temperature stability of lasing wavelength of GaAsSb/GaAs quantum well (QW) lasers grown by metal-organic
vapor phase epitaxy will be demonstrated. According to the best of our knowledge, this is the first trial of using
triethylgallium (TEGa) as the precursor to grow QW at low temperature (525°C). The lasing wavelength ranges from
1117 to 1144 nm and varies with temperature (dλ/dT) from 0.24 to 0.287 nm/K. These values are lower than other
previously reported results. The QW grown at high temperature (600 °C) by using trimethylgallium (TMGa) is also
examined. The lasing wavelength is 1125.6 nm at room temperature and dλ/dT is 0.36 nm/K, which is higher than those
lasers grown at lower temperature.
The RF-sputtered ITO layers were used as the transparency contact layer of the MSM PDs. The plasma gas would alter
the optical transmittance and the schottky barrier height between the ITO layer and InGaAsN absorption layer. Three
kinds of plasma gases were studied including Ar, Ar/N2, and Ar/O2. The Schottky barrier heights were 0.510 eV, 0.572
eV, and 0.574 eV when using Ar, (Ar/N2), and (Ar/O2) as the plasma gas; besides, the optical transmittances were
92.56%, 93.12% and 96%, respectively. Although the ITO film sputtered in the Ar/O2 ambient has highest transmittance
and Schottky barrier height, the high resistivity limited the photocurrent of the photodetectors; it is almost three orders
lower than the others. Consequently, using the Ar/N2 as the plasma gas would be a suitable choice regarding the MSM
photodetector application. The highest contrast ratio between photo-current and dark-current of the InGaAsN MSM
photodetectors were 5, 25 and 12 (measured under 0.2V) using Ar, Ar/N2, and Ar/O2 as the plasma gases.
The processing technology of 1.3&mgr;m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE will be
demonstrated. The threshold currents of the fabricated devices with 10 &mgr;m oxide-confined aperture are 0.7mA, which
correspond to 890A/cm2 threshold current density. And the threshold voltage of the device is 1.03V and maximum
output power is 33 &mgr;W. The series resistance is 85 &OHgr; which is 10 times lower then our preliminary work and 3 times
lower then intracavity contacted InAs-InGaAs quantum-dot VCSEL. This relatively lower resistance can even comparable with the best result reported in InGaAs oxide-confined VCSELs with intracavity contact.
In this paper, we demonstrate high performance 850 nm InGaAsP/InGaP strain-compensated MQWs vertical-cavity surface-emitting lasers (VCSELs). These VCSELs exhibit superior performance with threshold currents of ~0.4 mA, and slope efficiencies of ~ 0.6 mW/mA. High modulation bandwidth of 14.5 GHz and modulation current efficiency factor of 11.6 GHz/(mA)1/2 are demonstrated. We have accumulated life test data up to 1000 hours at 70°C/8mA. In addition, we also report a high speed planarized 850nm oxide-implanted VCSELs process that does not require semi-insulating substrates, polyimide planarization process, or very small pad areas, therefore very promising in mass manufacture.
Two approaches to realize the VCSEL devices based on GaAs substrates are investigated. The first approach utilizes InGaAs quantum wells with dilute nitride to extend the bandgap toward long wavelenegth. The second approach utilizes InAs/InGaAs quantum dots based on Stranski and Krastanov growth mode with confinement and strain combined to adjust the bandgap to 1.3 μm wavelength. High quality epitaxial layers with low threshold have been achieved with MBE and MOCVD. VCSEL performances that have been achieved are: Multimode operation at 1.303 μm with slope efficiency of 0.15 W/A (0.2 W/A), and maximum power of 1 mW (4 mW) for room temperature CW (pulse) operation have been achieved with MBE-grown In GaAaN active regions. Room temperature, CW single mode operation with SMSR > 40 dB at 1.303 μm has also been achieved with a slope efficiency of 0.17 W/A and maximum power of 0.75 mW also with MBE-grown InGaAaN active regions. In addition, MOCVD grown has also achieved a performance at 1.29 μm with slope efficiency, 0.066 W/A, and maximum power, 0.55 mW. VCSELs with 9 layers of quantum dots and all-semiconductor DBRs also achieved lasing at 1.3 μm.
We report our results on InGaNAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) for fiber-optic applications in the 1.3 μm range. The epitaxial structures were grown on (100) GaAs substrates by MBE or MOCVD. The nitrogen composition of the InGaNAs/GaAs quantum-well (QW) active region is 0 to 0.02. Long-wavelength (up to 1.3 μm) room-temperature continuous-wave (RT CW) lasing operation was achieved for MBE and MOCVD-grown VCELs. For MOCVD-grown devices with n- and p-doped distributed Bragg reflectors (DBRs), a maximum optical output power of 0.74 mW was measured for In0.36Ga0.64N0.006As0.994/GaAs VCSELs. The MBE-grown devices were made with intracavity structure. Top-emitting multi-mode 1.3 μm In0.35Ga0.65N0.02As0.98/GaAs VCSELs with 1mW output power have been achieved under RT CW operation. Emission characteristics of InGaNAs/GaAs VCSELs were measured and analyzed.