Low threshold current strained InGaAs/AlGaAs quantum well lasers

Citation

Eng, Lars E. (1993) Low threshold current strained InGaAs/AlGaAs quantum well lasers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wxtc-4x91. https://resolver.caltech.edu/CaltechETD:etd-08272007-091655

Abstract

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Strained InGaAs quantum well lasers offer the prospect of lower threshold currents, higher modulation speed, and lower linewidths than lattice matched GaAs quantum well lasers. In addition, the useful wavelength region of the GaAs material system is extended from 0.87[...] to beyond 1[...] with the addition of indium to the quantum well.

The lasers are fabricated using Molecular Beam Epitaxy (MBE) for the semiconductor layer structure. Liquid Phase Epitaxy (LPE) is then used to provide lateral optical mode and current confinement. Broad area threshold current densities of [...] is the first demonstration of high quality MBE grown strained InGaAs laser material. Measured transparency currents of 25[...] are a factor of two lower than in GaAs, which is consistent with a lower valence band density of states in the strained material. Buried heterostructure lasers made from this material with 2[...] wide stripe widths lase with a minimum threshold of 1.0mA (CW), the lowest value for a single quantum well laser with as-cleaved mirrors in any material system. With high reflectivity coatings (R=0.9) the first sub milliampere strained InGaAS lasers are obtained, with [...]. Details of the material growth, device fabrication, and device optimization are presented.

The broad gain bandwidth of single quantum well lasers is used to tune the lasing wavelength of optimized GaAs lasers over 125 nm and InGaAs lasers over 170 nm in an external cavity configuration. The measured tuning curves obtained for the InGaAs lasers are qualitatively different, and the difference can be attributed to the modified strained valence band strucure.

Low temperature (5°K) performance of low threshold lasers is investigated. The decrease in threshold with temperature is found to be linear over a range of 200°K for both GaAs and InGaAs with a larger decrease in threshold for the GaAs case. This result agrees well with a lowered valence band effective mass in the strained laser.

Thesis Files