
268 Gallium Nitride (GaN): Physics, Devices, and Technology
[116,121]. The broadening of the absorption peak can be as small as ~80 meV for the
most homogeneous samples. This absorption line is attributed to transitions from the
ground state of the conduction band, s, to the rst excited electronic state conned
along the growth axis, p
z
. The lateral connement in the QDs should give rise to
additional transitions under TE-polarized excitation. However, taking into account
the lateral dimension of the QDs, ~7 nm, the s–p
x,y
transitions should be masked by
the sapphire absorption for λ > 5 µm. The optical signature associated with s–p
x,y
was rst ...