Abstract
The incorporation of mismatched active regions in AlGaInP laser diodes facilitates engineering of the valence band energy levels by strain effects. Within the tensile strain regime this can lead to TM polarization of the laser emission as light hole-like sub-bands are promoted above the heavy hole-like. We have made a systematic study of the influence of strain on the threshold current, its temperature dependence, and the polarization characteristics of visible lasers, paying particular attention to short wavelength tensile strained devices. We have fabricated a series of single Q W lasers with a GaxIn1-xP well of a fixed width of 65 Angstroms and of varying composition to give both compressive (x < 0.51) and tensile (x > 0.51) strain; these were grown by MOCVD on a (100) substrate misorientated 100 the [111] direction to ensure a fully disordered alloy in the active region· The measured wavelengths of these devices range from 658 nm for x = 0.43 to 627 nm for x = 0.54. In Fig. 1, we show the threshold current of oxide isolated stripe geometry lasers as a function of temperature measured under pulse conditions. At low temperatures where there is no thermal leakage of carriers from the QW, the intrinsic improvements in the threshold current due to strain can be seen. In the high, temperature range, the increase in the band gap of the QW material going from compressive into tensile strain causes an increase in carrier leakage leading to a decrease in T0 (at 20° C) from 121 K for 0.63% compressive strain to 40K for 0.18% tensile starim Experiments are lu. progress to identify tire carrier leakage and recombination paths and, in particular, to separate intrinsic and extrinsic contributions to the excess leakage current.
© 1993 Optical Society of America
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