Terahertz electron distribution modulation in piezoelectric ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ multiple quantum wells using coherent acoustic nanowaves

We observed ultrafast electron distribution modulation following the strain oscillation of coherent acoustic nanowaves up to a THz frequency range. Through piezoelectric effects, the acoustic nanowave modifies the electronic subband structure, and further modulates the energy distributions of electrons and holes. With amplitude-fixed acoustic waves, a pronounced enhancement of transmission modulation due to acoustic modulation of electron distribution was observed when the optically probed energy position is close to the Fermi level.

Figure 1

Measured differentiated probe transmission changes versus probe delay (a) without and (b) with injecting excess carriers by Pump-2 at $\sim 16\mathrm{ps}$. The probe photon energy is $3.35\mathrm{eV}$.

Figure 2

Measured differentiated probe transmission changes versus probe delay (a) without and (b) with injecting excess carriers by Pump-2 at $\sim 16\mathrm{ps}$. The probe photon energy is $3.17\mathrm{eV}$.

Figure 3

Probe modulation enhancement versus carrier increase. The initial 2D carrier concentrations were (a) $1.35\times {10}^{13}{\mathrm{cm}}^{-2}$ and (b) $0.69\times {10}^{13}{\mathrm{cm}}^{-2}$. The enhancement is set as 0 without Pump-2 to inject excess carriers. The probe photon energy is $3.17\mathrm{eV}$.