Kevin J. Beernink

AlGaInP single quantum well laser diodes

The properties and low pressure organometallic vapor phase epitaxy of GaxIn1-xP/(AlGa)0.5In0.5P quantum well (QW) laser diode heterostructures with Al0.5In0.5P cladding layers, and having a wavelength of 614 < (lambda) < 690 nm, are described. At longer wavelengths ((lambda) > 660 nm), threshold current densities under 200 A/cm2 and efficiencies greater than 75% result from a biaxially compressed GaInP QW active region. Although short wavelength laser performance is diminished by the poor electron confinement afforded by AlGaInP heterostructures, good 630 nm band performance, and extension into the 610 nm band, is achieved with strained, single QW active regions.

TE/TM cross-polarization laser diodes using tensile-strained quantum wells

Polarization characteristics of TE/TM cross-polarization semiconductor laser diodes are discussed in this paper. Broad area lasers fabricated from tensile strained In0.5+(delta )Ga0.5-(delta )P/(AlGa)0.5In0.5P quantum well laser structures oscillate in TE/TM dual polarizations. Polarization dominance changes from TE to TM as the cavity length of the laser is increased from 250 micrometers to 650 micrometers. The polarization-dependent gain property of a tensile-strained quantum well laser is analyzed from a simple theoretical model. In a slightly tensile strain quantum well, where light-hole and heavy-hole ground states are nearly degenerate in the valence band due to the strain and quantization effect, gain is provided for TM and TE modes simultaneously, and the two mode gain curves cross at certain injection level. Polarization switching is made possible by changing the threshold gain of the laser. The threshold gain dependent polarization switching is utilized to fabricate closely spaced independently-addressable dual beam cross polarization lasers. Results on 650 nm broad area dual beam cross polarization laser are presented. For dual polarization infrared lasers, a dual quantum well structure in which gains for TE and TM modes are provided by lattice-matched and tensile-strained quantum wells separately is designed. Eight-hundred-thirty-five nm broad area laser fabricated from a GaAs and GaAs0.95P0.05 dual quantum well structure oscillating in TE/TM dual polarizations is demonstrated.

Dual-wavelength laser by selective intermixing of GaAs/AlGaAs quantum wells

The longer-wavelength quantum well in an AlGaAs/GaAs asymmetric dual quantum well laser structure was selectively removed by localized intermixing. High Si-doping on each side of the longer-wavelength well caused intermixing during an anneal under a SiNx cap, while leaving the other nearby well intact. During an anneal under an exposed GaAs surface layer, both quantum wells remained intact. By patterning the surface with alternating SiNx and exposed GaAs, the longer-wavelength quantum well was selectively intermixed under the SiNx. Integrated broad area lasers were fabricated with threshold current density and external quantum efficiency of 260 A/cm2 and 30%/facet at a wavelength of 751 nm in capped regions and 195 A/cm2, 32%/facet at 824 nm in the uncapped regions. This technique can be used to fabricate close spacing multi-wavelength laser arrays.

Simple models for the threshold, efficiency, and polarization of AlGaInP red laser diodes

The temperature dependence of threshold current and quantum efficiency for GaxIn1- xP (x equals 0.4, 0.6; (lambda) equals 680, 633 nm) single 80 angstrom quantum well lasers is analyzed using a model for the electron leakage current. This model fits the experimental data, correctly describing the rapid increase in threshold and drop in quantum eficiency as temperature increases. Also it indicates that the drift component of the electron leakage current is important, because of the poor p-type conductivity in AlGaInP. In addition, a single quantum well Ga0.5+(delta )In0.5-(delta )P/(AlGa)0.5P laser structure is demonstrated, which can provide similar gain in both polarizations. The slightly-tensile- strained quantum well has the light hole ground state, which gives the lowest transparency current for TM-mode gain. However, the TE-mode gain is dominant at high drive currents. The gain-current relationships have been characterized for each polarization, and found to cross at a modal gain value of 25 cm-1. Lasers whose threshold gain is near this crossover value were found to emit in either one or both polarizations, with a very wide range of polarization assymetry possible. A simple QW gain model can be used to describe this behavior.