3.4 QUANTUM DOT LASERS
Room-temperature QD lasers are expected to exhibit high performance with
large gain, differential gain, and modulation bandwidth. Moreover, the QDs have
demonstrated low threshold current density and reduced temperature dependence
of the threshold current density [32]. These performance features are directly the
result of zero-dimensional carrier confinement and discrete density of states of
QDs. For instance, the symmetric gain shape of QD lasers leads (through
Kramers–Kro
¨
nig relation) to low index of refraction change at the peak gain
wavelength, therefore, QD lasers exhibit near zero LEF. As shown previously,
LEF for InGaAs- and InGaAsP-strained QW lasers (see Figure 3.6) are on the
order of 2 or higher. Recently, it has