R.P. Schneider

Fabrication and performance of selectively oxidized vertical-cavity lasers

We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range.<<ETX>>

Cavity characteristics of selectively oxidized vertical‐cavity lasers

We show that a buried oxide layer forming a current aperture in an all epitaxial vertical‐cavity surface emitting laser has a profound influence on the optical and electrical characteristics of the device. The lateral index variation formed around the oxide current aperture leads to a shift in the cavity resonance wavelength. The resonance wavelength under the oxide layer can thus be manipulated, independent of the as‐grown cavity resonance, by adjusting the oxide layer thickness and its placement relative to the active region. In addition, the electrical confinement afforded by the oxide layer enables record low threshold current densities and threshold voltages in these lasers.

Modal analysis of a small surface emitting laser with a selectively oxidized waveguide

We describe studies of an index‐guided ∼4×3 μm2 vertical cavity surface emitting laser with a cw, room temperature 133 μA threshold current and 53% slope efficiency fabricated using selective wet thermal oxidation to provide optical and electrical confinement. While the device operates strictly single mode, a large number of transverse modes are evident in the subthreshold luminescence observed in both vertical and lateral directions. Despite the lumped nature of the index region, the transverse mode wavelengths agree very well with those predicted for a conventional distributed waveguide structure. Waveguide dimensions and an effective index step of 2% between the active and cladding region are determined by fitting the modal data.

Vertical cavity surface emitting lasers with 21% efficiency by metalorganic vapor phase epitaxy

Proton implanted, vertical cavity top-surface emitting lasers exhibit the highest single-mode and multi-mode output powers, highest power conversion efficiency, and lowest threshold voltage for such devices reported to date. These lasers use new mirror grading designs that are enabled by metalorganic vapor phase epitaxys capabilities of alloy grading and carbon doping. The results validate this growth technology by exceeding the previous best results which were based on molecular beam epitaxy.<<ETX>>

UNIPARABOLIC MIRROR GRADING FOR VERTICAL CAVITY SURFACE EMITTING LASERS

We report details of mirror grading profiles for high efficiency vertical cavity surface emitting lasers. The mirrors provide low vertical resistance in conjunction with improvements in optical reflectivity, thermal conductivity, and lateral electrical conductivity in comparison to earlier grading profiles. The enhancement of these properties is verified by a comparison of thermal resistance and total electrical resistance for lasers of varying size.

Microstructures of (In,Ga)P alloys grown on GaAs by metalorganic vapor‐phase epitaxy

The microstructures of metalorganic vapor‐phase epitaxy alloys of (In,Ga)P grown on GaAs substrates were examined using transmission electron microscopy. Alloys examined were grown at 600–775 °C on substrates at or near (001) or (113)A using growth rates of 0.69 and 0.17 nm/s. Two common semiconductor alloy phenomenon, ordering and phase separation, were studied over this range of growth conditions. The CuPt‐type ordering reflections are sharpest for growth at 675 °C and more diffuse at 600 and 725 °C due to higher densities of antiphase boundaries. Order can be eliminated by growth at 750 °C or above to obtain the highest band gaps and optical emission energies. Detailed investigation of the microstructure for growth at 675 °C indicates that ordered domains are platelets consisting of thin (1–2 nm) lamella on (001) planes that alternate between the two {111}B ordering variants, in agreement with a model proposed by others. We have formed ‘‘unicompositional’’ quantum wells with sharply defined ordered lay...

Index guiding dependent effects in implant and oxide confined vertical-cavity lasers

Implant and oxide confined vertical-cavity surface-emitting lasers are compared in terms of properties dependent upon the nature of index guiding in the two structures including CW threshold current scaling with size, light-current linearity, pulsed operation delay, and beam profiles. The oxide confined lasers, fabricated by wet thermal oxidation, have a built-in index guide and thus exhibit substantially better properties than do lasers from the same wafer fabricated by proton implantation which rely on a thermal lens to reduce diffraction losses.

Growth and characterization of GaInP unicompositional disorder‐order‐disorder quantum wells

Metalorganic vapor phase epitaxy (MOVPE) is used to grow unicompositional quantum‐well (QW) structures, in which the QW and barrier layers are composed of ordered and disordered GaInP, respectively. Transmission electron dark‐field micrographs reveal abrupt interfaces between highly ordered QWs and disordered barriers, with no evidence of defect formation. Low‐temperature photoluminescence from the structures exhibits relatively broad emission peaks, with emission energy increasing with decreasing QW thickness. The dependence of emission energy on well thickness can be described by a finite square well model only when a type‐II band alignment is taken for the heterostructure, in which the conduction band edge of the ordered GaInP QW lies about 135–150 meV below that of the disordered barrier material. These results demonstrate a high degree of control over the ordering process in MOVPE, such that quantum size effects can be realized solely through disorder‐order phenomena. Further, the data provide strong...

Photoluminescence linewidths in metalorganic vapor phase epitaxially grown ordered and disordered InAlGaP alloys

The dependence of the photoluminescent properties of In0.48(AlyGa1−y)0.52P alloys (0≤y≤0.5) on growth temperature and substrate misorientation off GaAs(100) has been studied. Samples were grown using low‐pressure metalorganic vapor phase epitaxy. By studying the dependence of ordering behavior in InGaP as a function of substrate misorientation and growth temperature simultaneously, a very large range in low‐temperature photoluminescence emission energy—135 meV—has been obtained. The photoluminescence linewidth exhibits a strong, continuous dependence on the extent of atomic ordering (the emission energy) in the alloys. The results indicate that inhomogeneity in the microstructure of the material (i.e., between ‘‘ordered’’ domains and the ‘‘disordered’’ matrix) is the dominant photoluminescence broadening mechanism. This investigation has allowed a significant optimization of the optical properties of these materials, including the narrowest low‐temperature photoluminescent linewidths reported for all of t...

Efficient room-temperature continuous-wave AlGaInP/AlGaAs visible (670 nm) vertical-cavity surface-emitting laser diodes

Significant improvement in the performance of AlGaInP/AlGaAs visible vertical-cavity surface-emitting laser diodes has been achieved in gain-guided planar-geometry devices utilizing proton implants to define the current injection path. Threshold currents as low as 1.25 mA were measured on 10 /spl mu/m-diameter devices, with maximum power output of 0.33 mW from larger devices. Continuous-wave (cw) lasing was achieved at temperatures as high as 45/spl deg/C. The improved diode performance is attributed to better lateral heat-sinking and reduced parasitic heat generation afforded by the planar device structure, relative to previously-reported air-post structures. This work represents the first realization of efficient room-temperature operation of AlGaInP-based visible VCSEL diodes.<<ETX>>