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.
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.
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.
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.
We have successfully developed a selective surface coating technique to control the modal behavior of the ionimplanted vertical cavity surface emitting laser. Using selective deposition of germanium coating by lift-off process, we could spatially control the threshold gain condition of the VCSEL to support the single transverse mode. The threshold current is 7 mA and single transverse mode operation is maintained up to 1 mW. The method is simple and nondestructive compared to other techniques.
Resonant-cavity light-emitting diodes (RCLEDs) are attractive light sources because of their applications in data communications, optical printing, display, and optical interconnects. Lower intensity LEDs with a modulation bandwidth of few hundred MHz are suitable for lower-speed optical fiber communications. In this work, we have made oxide-confied AlGaAs/GaAs RCLEDs for optical communication systems. The epitaxial layers of the RCLEDs were grown by MBE system on the N+-GaAs substrates. T he RCLED epitaxial layers mainly consisted of an n-type DBR (diffractive Bragg reflector), a p-type DBR, and an active region sandwiched between p- and n-type DBR's. The thickness of the optcal cabity is 1$lamda. Reflectance measurement of the RCLED expitaxial wafers showed that the resonance of the RCLED cavity were about 850 nm. The wet oxidation process, which defined the current conducting aperture, was done at 425 degree(s)C under nitrogen flow with steam. P-ohmic and n-ohmic contacts were then formed sequentially using electron beam evaporation and annealing. The optical power of the RCLED is measured as function of current and temperature. The beam pattern and the optical spectrum were also measured and analyzed.
In this work, we have made AlGaAs/GaAs gain-guided broad- area vertical-cavity surface-emitting lasers (VCSELs) in the 850-nm range. For higher power applications such as optical pumping and optical communications, board-area VCSELs and VCSEL arrays are needed. The distributed Bragg reflectors (DBRs) of the VCSELs consist of Al0.12Ga0.88As/AlAs quarter-wave stacks. The GRINSCH active region is consisted of an undoped three-quantum-well GaAs/Al0.3Ga0.7As, two undoped Al0.3Ga0.7As confinement layers, and two undoped linearly graded AlxGa1-xAs layers. The current confinement of the VCSELs was made by proton implantation with an implantation energy of 280 KeV. The emitting window diameters are 30 to 50 (mu) m. A very high cw optical power of 23.4 mW and a pulsed optical power of over 36 mW were measured for a 50-(mu) m aperture device. These VCSELs are suitable for higher power applications. The VCSELs showed multiple transverse mode characteristics. The near-field characteristics and spectrum of the devices were measured and analyzed. The modulation characteristics of the VCSELs were also measured. A 3 dB bandwidth (f3dB) of 5.6 Ghz was measured for a 30-(mu) m aperture device at 20mA.
We have made AlGaAs/GaAs gain-guided two-dimensional (8x8 and 4x4) vertical-cavity surface-emitting laser array in the 850-nm rage for optical communication applications. Higher optical power with nearly single transverse mode output can be achieved by using high-density two-dimensional VCSEL arrays with smaller emitting element windows (<EQ 5(mu) m). The distributed Bragg reflectors (DBRs) of the VCSELs consist of A10.12Ga0.88As/AlAs quarter-wave stacks. The GRINSCH active region is consisted of an undoped three- quantum well GaAs/Al0.3Ga0.7As and two undoped linearly graded AlxGa1-xAs confinement layers. The emitting windows of the individual VCSEL elements are 5 (mu) mx4 (mu) m. A high cw optical power of 15.3 mW was measured for a 8x8 array, with a maximum pulsed optical power of 28 mW at 160 mA. The spectrum of the VCSEL array showed single transverse mode characteristics. The near-field characteristics of the arrays were measured. Almost all the VCSEL elements emitted TEM00 mode. The modulation characteristics of the VCSEL arrays were also measured at different operating current.
We report the results of the AlGaInP/InGaP broad area laser diodes.the broad area lasers were made with laser cavity- lengths of 250 micrometers to 1.25 mm. The pulsed L-I characteristics of these broad area lasers were measured, as a function of the laser stripe width. The pulse width of the pulsed L-I measurements was 360 nsec and the pulse periods were 10 msec to 5 (mu) sec. The measured pulsed L-I characteristics of the AlGaInP/InGaP lasers were found to be strongly dependent on the duty cycles of the applied voltage pulses, which were attributed to heating effects within the broad area lasers. The threshold current increases with increasing pulse duty cycle, while the external quantum efficiency decreases with increasing duty cycle. Heating effects were negligible only at very low duty cycles of 0.1 percent or below. Similar pulsed L-I measurements were performed on the 850-nm AlGaAs/GaAs broad area lasers. Heating effect was not observed in those measurements because of better heat conduction properties of the AlGaAs cladding layers. The results were carefully analyzed.