Three-region characteristic temperature in p-doped quantum dot lasers

We have investigated the temperature dependence of threshold in p-doped 1.3 mu m InAs/GaAs quantum dot (QD) lasers with ten layers of QDs in the active region. It is found that the dependence of threshold current density on the temperature within the temperature range from 10 to 90 degrees C can be divided into three regions by its characteristic temperature (T-0): negative, infinite, and positive T-0 regions. Furthermore, the T-0 region width is dependent on the cavity length: the longer cavity length of the QD lasers correspondingly the wider T-0 region. Additionally, for the broad area laser, the threshold modal gains of the lasers with different cavity lengths can be fitted by an empirical expression as a function of the threshold current density, when at the temperatures of 30, 50, and 70 degrees C. We find that the transparency current density (J(tr)) remains almost unchanged under different temperatures according to the extracted parameters from these fitted results, which indicates that J(tr) plays an important role in balancing the T-0 between negative region and positive one. (C) 2014 AIP Publishing LLC.