Photomodification of carrier lifetime and diffusivity in AlGaN epitaxial layers

• AlGaN layers were photomodified without surface damage by intense laser pulses.
• During modification, high-density photoexcited carriers activated new defects.
• These defects permanently reduced free carrier nonradiative lifetime and IQE.
• Photomodification susceptibility increases with Al content in the AlGaN layers.
• A short laser photomodification also permanently enhanced the carrier diffusivity.

Nonradiative recombination rate and diffusivity of nonequilibrium carriers were modified by intense laser pulses in AlGaN epilayers with Al content ranging from 16 to 71%. The epilayers were examined before and after the photomodification using light-induced transient grating and photoluminescence spectroscopy techniques. The photomodification resulted in (i) enhancement of the nonradiative recombination rate and (ii) large changes of the diffusion coefficient of the nonequilibrium carriers, without imposing any macroscopic structural damage to the epilayers. The photomodification effect on the recombination rate was stronger in the layers with higher Al content indicating the involvement of the Al atoms in this process. The carrier diffusivity exhibited a rapid initial increase as a consequence of the photomodification followed by a slow decline, as the photomodification duration was increased. The enhancement of the diffusion coefficient of up to 2.4 times was accompanied by 13% decrease in the carrier lifetime.