Diode lasers operating at 3 µm in continuous wave mode at room temperature were fabricated using metamorphic molecular beam epitaxy. The laser heterostructures have a lattice constant 1.3–1.6% bigger than that of the GaSb substrates. The mismatch between the epi-structure and the substrate lattice constants was accommodated by a network of misfit dislocations confined within linearly compositionally graded buffer layers. Two types of the buffers were tested—GaInSb and AlGaInSb. The laser heterostructures with Al-containing buffer layers demonstrated better surface morphology and produced devices with lower threshold and higher efficiency. At the same time the use of Al-containing buffers caused an excessive voltage drop across the laser heterostructure. Thus, a maximum continuous wave output power of 200 mW was obtained from lasers grown on GaInSb buffers, while only 170 mW was obtained from those grown on AlGaInSb buffers.
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