Pb1−xSnxTe heterostructures have been grown by liquid phase epitaxy on p-PbTe substrates and laser diodes have been fabricated from layered structures with the following compositions: n-PbTe (LPE)/p-PbTe (substrate); n-Pb1−xSnxTe (LPE)/p-PbTe (substrate); and n-PbTe (LPE)/n-Pb1−xSnxTe (LPE)/p-PbTe (substrate). Lasing in all structures occurs in the lower-band-gap region. Threshold currents in these lasers are comparable to those reported for conventional diffused lasers, indicating that the presence of the heterojunctions does not introduce a significant number of new nonradiative recombination centers and that efficient minority carrier injection occurs across the heterojunctions. The liquid phase epitaxy technique used in these growths is discussed.
A systematic study has been made of the effect of the middle active region width in double heterojunction Pb1−xSnx Te/PbTe laser diodes on the lasing threshold. A fourfold reduction in pulsed threshold over that of comparable single heterojunction lasers is demonstrated in lasers having 4-μm-wide middle regions. A comparison is also made between lasers fabricated by liquid phase epitaxy using undoped melts and substrates, and using thallium-doped p -type PbTe layers; the latter is shown to yield thresholds as much as two times lower.
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