Time-Resolved Reflectivity Studies of Carrier Dynamics as a Function of Al Content in AlGaN Alloys

Abstract

We have used intensity dependent pump–probe reflectivity measurements to investigate the carrier dynamics in AlGaN alloys with Al content ranging from ∼0.15 to 0.4. For the Al0.15Ga0.85N sample the intensity dependence of the ΔR decay suggests that at high intensity the shallow traps are saturated and ultrafast nonradiative recombination dominates the carrier dynamics. For the Al0.25Ga0.75N and Al0.4Ga0.6N samples ΔR decays faster with decreasing intensity and changes sign. Moreover, the decays are faster for a given intensity in the higher Al content sample. This behavior suggests that in these cases the dynamics are governed by trapping at localized states that become deeper and more numerous as the Al content increases. Within this context the sign change in ΔR may reflect the onset of photoinduced absorption associated with the excitation of carriers from the localized states to the bands.