Bismuth-doped Pb1-xSnxTe diode lasers with low-threshold currents

Diode lasers have been fabricated from Bi-doped Pb
1-x
Sn
x
Te with
0.24 \leq x \leq 0.27
, which have threshold current densities as low as 1400 A.cm
^-2
at 77°K and 71 A.cm
^-2
at 12°K, whereas diodes fabricated from undoped Pb
1-x
Sn
x
Te> in this composition range did not exhibit laser action for current densities up to 30 000 A.cm
^-2
at 77°K and had threshold current densities greater than 200 A.cm
^-2
at 12°K. Bi doping also results in a reduction in the annealing times required to form suitable
p-n
junctions from several weeks to a few days. These effects can be tentatively related to an increased electron concentration in the
n
-type layer due to the addition of Bi, a donor impurity. A curve of
Eg
versus
x
for
0 \leq x \leq 0.4
, which agrees with predictions, is presented.