Turn-on time delay of vertical cavity surface emitting lasers of different active region diameters

In this paper, we investigated the turn-on time delay (t
on
) of vertical cavity surface emitting laser as a function of active region diameter (D). The analysis is performed according to the influence of D on the threshold carrier density (N
th
) and cavity volume. At small D, t
on
takes a very high value due to high value of N
th
. The latter increases as D decreases due to increasing of diffraction loss which dominates at small D. While as D increases, the cavity volume increases which leads to deplete the carrier density inside the active region and therefore increase t
on
. We show that there is an optimum value of D that gives a minimum t
on
and threshold current.