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Improved yellow-spectrum double-heterojunction In1−xGaxP1−zAsz laser diodes constructed by LPE on VPE GaAs1−yPy substrates are described. The lattice-matched LPE quaternary alloy growth process is outlined, as well as the need for complete melt removal between the growth of each heterojunction layer, which is more difficult for In-rich melts than for Ga-rich melts when lattice match is a problem. Over two times lower threshold current densities are demonstrated (Jth?3.6×103 A/cm2, λ?5920 Å, 77 °K) than for the first reported diodes of this type. The temperature dependence of laser threshold current density is presented in the range 4.2–200 °K. The threshold current density can be approximated as Jth∝exp(T/T0) with T0?52 °K in the range 50–175 °K, which compares well with red-orange AlGaAs double heterojunctions (T0?42 °K) having greater heterobarriers. Laser operation in the yellow-orange portion of the visible spectrum at ∼200 °K is demonstrated. These results on thick (1.5 μm) active layer diodes, having relatively small heterobarriers (ΔE∼65 meV), indicate that further improvement and control of the quaternary growth process will lead to still lower threshold currents and higher-temperature operation in the orange-yellow.
Coleman et al. (Sat,) studied this question.