Dynamical behavior of dense carriers has been assessed at room temperature
(RT) in the InGaN multi quantum well (MQW) based laser diodes (LDs) by empl
oying pump and probe (P&P) spectroscopy under the pulse width of 150 fs. Th
e LDs are composed of InxGa1-xN-InyGa1-yN MQWs [(a), x = 0.1, y = 0.02; (b)
, x = 0.2, y = 0.05 and (c), x = 0.3, y = 0.05], whose stimulated emissions
correspond to near ultraviolet (390 nm), violet (420 nm) and blue (440 nm)
, respectively. The optical gain was contributed from the nearly delocalize
d states [the lowest-quantized MQW levels (LQL)] in the sample (a), while i
t was from highly localized levels with respect to LQL by 250 meV for the s
ample (b), and by 500 meV for the sample (c). It was found that the photo-g
enerated carriers rapidly (less than 1 ps) transferred to LQL, and then rel
axed to the localized tail within the time-scale of several ps, giving rise
to the optical gain. Such gain spectra were saturated and other bands appe
ared in the vicinity of LQL under higher photo-excitation. (C) 2001 Elsevie
r Science B.V. All rights reserved.