Lead strontium telluride and lead barium telluride grown by molecular-beam epitaxy

Abstract

Long wavelength diode lasers operating in the 3–10-μm wavelength range are of interest as optical sources for future fiber optics communications and sensor systems. PbEuSeTe large optical cavity single quantum well diode lasers have so far attained the highest operating temperatures (174 K cw, 280 K pulsed) in this wavelength range. Two alternative materials systems PbSrTe and PbBaTe have now been grown for the first time by molecular-beam epitaxy. The choice of these ternaries was motivated by the fact that SrTe and BaTe have the same face-centered-cubic crystal structure as PbTe and roughly comparable lattice constants, but much larger energy band gaps. In the Pb1−xSrxTe system, x-ray diffraction studies show clear evidence of phase segregation for x>0.15. The carrier mobilities decrease monotonically with strontium concentration in the single phase region, which suggests that disorder-related scattering is dominant. The energy band gap increases approximately as dEg/dx=3.2 eV for small x, and the index of refraction decreases monotonically with increasing x. In the Pb1−xSrxTe system, a combination of x-ray diffraction, energy band gap and other data clearly demonstrate that the solubility of BaTe in PbTe is limited to about 4%, possibly because of the relatively large difference in lattice constants between PbTe (6.460 Å) and BaTe (7.001 Å). These results imply that PbSrSeTe grown lattice matched to PbTe is a promising material system for long wavelength diode lasers and light emitting diodes.