Comparing the results of the quantum well laser diode simulator Minilase-II with modulation responses measured at the University of California, Santa Barbara, we show that electron and polar optical phonons are rapidly heated above equilibrium in conventional injection lasers. This heating essentially follows and counteracts the modulation of the carrier density, leading to degradation of the dynamic laser response even for relatively small changes in carrier temperature. With this in mind, we speculate about the use of tunneling injection to avoid the hot quantum carrier effects intrinsic to conventional injection lasers. ©1997 American Institute of Physics.