Effects of substrate heating on the spatial uniformity of threshold current and emission wavelength in GaAs and InGaAs graded-index separate-confinement heterostructure quantum-well lasers grown by molecular-beam epitaxy

We show that if the active region of a quantum‐well (QW) laser is grown at a high temperature such that the sticking coefficients of group III species are less than unity, the emission wavelength λ and threshold current density Jth are sensitive to the spatial variations in substrate growth temperature Ts despite the time average flux variations of less than 1% across the surface of a rotating 7.5 cm diam substrate in our molecular‐beam epitaxy system. InGaAs strained QW lasers, in which the active region is grown at Ts < 580 °C at which In and Ga have unity sticking coefficients, have uniform Jth (212±4 A cm−2) and λ(989±1 nm) on a 5 cm diam substrate. These lasers were grown with In mounting. In contrast, GaAs QW lasers, which are grown at ∼700 °C with In mounting, have less uniform Jth (395±20 A cm−2) and λ(850±9 nm). This is the result of nonuniform substrate heating which is partly due to voids in the In back coating. This causes variations in GaAs growth rate because of the high temperature dependen...