  We report temperature-dependent current-voltage (I - V - T) and output light
power-voltage or current (P - V - T) or (P - I - T) characteristics of 1550 nm
tunneling injection quantum dot (TI QD) laser diodes. Experimental data is
accompanied by physical models that distinguish between different current flow
and light emission mechanisms for different applied voltages and temperature
ranges. Three exponential regimes in the I - V characteristics were identified
for low bias levels where no optical radiation takes place. At the lowest bias
levels, the diffusion-recombination mechanism based on the classical
Shockley-Reid-Hall theory dominates. This is followed, at low and near room
temperature, by a combination of weak tunneling and generation-recombination,
respectively. In the third exponential region, for all temperatures carrier
transport is dictated by strong tunneling, which is characterized by a
temperature-independent slope of the I - V curves and a variable ideality
factor. The I - V results were compared to a conventional QD laser in which the
current flow mechanisms of the first and third types are absent, which clearly
demonstrates the key role played by the TI layer.
  In the post-exponential voltage range, when the diodes are in the high
injection regime, the characteristics of the two types of diodes are identical.
The typical behavior at the threshold current, where the output power increases
fast has a clear signature in the I - V characteristics. Finally, an analytical
quantitative relationship is established between the light output power and the
applied voltage and current as well as the carrier density participating in
radiative recombination.
