Properties of Bi-doped PbTe epitaxial layers and pn junction diodes grown by TDM-CVP

Effects of Bi-doping in PbTe liquid-phase epitaxial layers grown by the TDM-CVP have been investigated. For Bi concentration in the solution, x_Bi, lower than 0.2 at.%, Hall mobility is low. In contrast, for x_Bi>0.2 at.%, Hall mobility is high, while carrier concentration is in the range 10¹⁷ cm⁻³. However, ICP emission analysis shows that, for x_Bi=1.0 at.%, Bi concentration in epitaxial layer is N_Bi=2.3–2.7×10¹⁹ cm⁻³.These results indicate that Bi behaves not only as a donor but also as an acceptor; the nearest neighbor or very near DA pairs are formed. Carrier concentration for Bi-doped layers takes a minimum value at a Te vapor pressure of 2.2×10⁻⁵ Torr for growth temperature 470°C, which is coincident with that of the undoped PbTe. And broad contact pn junctions with highly Bi-doped layers easily cause laser emission compared to undoped junctions. The result suggests that the nearest lattice site Bi–Bi DA pairs behave as strong radiative centers in PbTe.