M.H. MacDougal

Ultralow threshold current vertical-cavity surface-emitting lasers with AlAs oxide-GaAs distributed Bragg reflectors

An electrically-pumped, vertical-cavity, surface-emitting laser (VCSEL) using an AlAs oxide-GaAs DBR above the AlGaAs-GaAs-InGaAs gain region and a conventional AlAs-GaAs DBR below is described. By selective oxidation, devices with current flow apertures of different areas are fabricated, and in 8-/spl mu/m-square devices, threshold currents as low as 0.22 mA are achieved. Being the first electrically-pumped VCSEL to utilize the oxide-based DBR, it demonstrates that the oxide-based DBR is of sufficient quality to realize submilliampere threshold currents.<<ETX>>

Electrically-pumped vertical-cavity lasers with Al x O y -GaAs reflectors

We have fabricated the first electrically-pumped vertical-cavity surface-emitting lasers (VCSELs) which use oxide-based distributed Bragg reflectors (DBRs) on both sides of the gain region. They require a third the epitaxial growth time of VCSELs with semiconductor DBRs. We obtain threshold currents as low as 160 /spl mu/A in VCSELs with an active area of 8 /spl mu/m/spl times/8 /spl mu/m using a two quantum well InGaAs-GaAs active region. By etching away mirror pairs from the top reflector, quantum efficiencies as high as 61% are attained, while still maintaining a low threshold current of 290 /spl mu/A.

Influence of mirror reflectivity on laser performance of very-low-threshold vertical-cavity surface-emitting lasers

The influeuce of mirror reflectivity on laser performance of InGaAs-GaAs vertical-cavity surface-emitting lasers fabricated by selective oxidation is investigated by the stepwise change of the number of pairs in top mirror stack after device fabrication. Devices with 18-pair stacks in the top mirror, which is the optimized number of pairs in this structure, show an output power over 1.9 mW and a slope efficiency of 55% while maintaining a low threshold current of 212 /spl mu/A. The analysis of the threshold current and differential efficiency related to mirror reflectivity shows an internal quantum efficiency of 95%, an internal round-trip loss of 0.072, and a transparency current density of 71 A/cm/sup 2/.<<ETX>>

Design and fabrication of VCSELs with Al/sub x/O/sub y/-GaAs DBRs

A procedure for fabricating vertical-cavity surface-emitting lasers (VCSELs) with oxide-based distributed Bragg reflectors (DBRs) is presented. An in-depth analysis of parameters and behavior unique to oxide VCSELs determines the device design. The development cycle time for these devices is reduced through development of a method for post-growth analysis of the epitaxial stack reflectivity before device processing. Threshold currents as low as 160 /spl mu/A and resistances as low as 80 /spl Omega/ are demonstrated using different device designs. The total optical loss of low-doped oxide VCSEL structures is 0.163% which is comparable to VCSEL designs based on all-semiconductor DBRs. The thermal resistance of an 8/spl times/8 /spl mu/m VCSEL is measured to be 2.8/spl deg/C/mW, demonstrating that the presence of oxide layers does not act as a barrier to heat flow out of the active region.

Lasing characteristics of high-performance narrow-stripe InGaAs-GaAs quantum-well lasers confined by AlAs native oxide

High-performance narrow-stripe InGaAs-GaAs quantum-well lasers with integral buried AlAs native-oxide layers have been fabricated. AlAs native-oxide layers above and below waveguide region were employed for current and optical confinement to form narrow-stripe lasers. A low temperature (400/spl deg/C) anisotropic wet oxidation technique was used to selectively oxidize AlAs layers in the epitaxial structure. The devices demonstrated continuous wave threshold currents of 3.5 mA, external quantum efficiencies of 82%, and a characteristic temperature of 133 K for 1.8 /spl mu/m-wide aperture, 400 /spl mu/m-long devices. Threshold currents of 1.7 mA were obtained by applying HR/HR coatings.

High-speed high-temperature operation of vertical-cavity surface-emitting lasers

Vertical-cavity surface-emitting lasers emitting at 850 nm have been developed that are capable of 10-Gb/s operation at high temperatures. Measurements are made at 10 and 12.5 Gb/s at temperatures up to 150/spl deg/C.

Low resistance intracavity-contacted oxide-aperture VCSELs

The authors study, analytically and experimentally, the extrinsic series resistance in intracavity-contacted vertical-cavity surface-emitting lasers (VCSELs). Low resistance, low threshold-current, intracavity-contacted VCSELs are fabricated, with resistances ranging from 355 /spl Omega/ for 4-/spl mu/m square apertures to 80 /spl Omega/ for 12-/spl mu/m square apertures and threshold voltages as low as 1.35 V. To the best of our knowledge, these are the lowest values reported for this type of VCSEL. The threshold currents range from 270 /spl mu/A for 4 /spl mu/m/spl times/4 /spl mu/m apertures to 850 /spl mu/A for 12 /spl times/12 /spl mu/m. From a comparison of the resistance as a function of oxide aperture radius, the measured data follows closely with the calculated data, demonstrating the validity of the derived expressions for series resistance.

Wavelength shift of selectively oxidized Al/sub x/O/sub y/-AlGaAs-GaAs distributed Bragg reflectors

The effect of multiple oxidations on Al/sub x/O/sub y/-GaAs DBRs and Al/sub x/O/sub y/-AlGaAs-GaAs DBRs is investigated. With a compositionally graded AlGaAs layer, the oxide DBR remains stable under thermal stress, whereas without it, the DBR fractures. The stopband of the oxide DBR with the AlGaAs layer shifts when sequenced through multiple oxidation processes, which is attributed to the vertical oxidation of the AlGaAs. The resonance wavelength of a Fabry-Perot cavity containing an oxide DBR shifts 6 nm after 30 min of additional oxidation at 425/spl deg/C.

Thermal impedance of VCSELs with AlO/sub x/-GaAs DBRs

The authors have measured the thermal impedance of vertical-cavity surface-emitting lasers (VCSELs) with oxide/GaAs DBRs and shown that it is comparable to that of VCSELs with all-semiconductor DBRs. A VCSEL with an 8-/spl mu/m oxide aperture shows a thermal impedance of 2.8/spl deg/C/mW. By varying the aperture size, the thermal conductance of the material below the active area is 0.255 W/cm/spl deg/C. These results demonstrate that the oxide is not a major barrier to heat transport out of the active region.

Low dark current InGaAs detector arrays for night vision and astronomy

Aerius Photonics has developed large InGaAs arrays (1K x 1K and greater) with low dark currents for use in night vision applications in the SWIR regime. Aerius will present results of experiments to reduce the dark current density of their InGaAs detector arrays. By varying device designs and passivations, Aerius has achieved a dark current density below 1.0 nA/cm2 at 280K on small-pixel, detector arrays. Data is shown for both test structures and focal plane arrays. In addition, data from cryogenically cooled InGaAs arrays will be shown for astronomy applications.