Limitations of the direct-indirect transition on In1−xGaxP1−zAsz heterojunctions

Abstract
Because In1−xGaxP1−zAsz is the highest‐energy direct‐gap alloy employed in laser diodes, we attempt to establish where the direct‐indirect transition (xc+0.516yc=1.235, 77 °K) hinders or possibly even limits the use of this sytem in large‐barrier (ΔE∼250 meV) double‐heterojunction (DH) structures. The behavior at 300 and 77 °K of the IV characteristics of single‐heterojunction and homojunction structures employing high Ga composition (x?0.72, z≲0.01) wide‐gap In1−xGaxP1−zAsz layers, lattice matched on GaAs1−yPy substrates, show that the nature of the direct‐indirect transition of the ternary boundary In1−xGaxP (xxc, y=1 or z=0) acts as a limiting factor on the DH diode and laser performance of the quaternary system. As in GaAs1−yPy, donor states associated with subsidiary minima (X) cause a premature onset of the direct‐indirect transition, and limit the growth of lattice‐matched large‐barrier In1−xGaxP1−zAszE∼250 meV) DH lasers, with all layers direct, to substrates of composition y≲0.40.

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