Hot-phonon-assisted absorption at semiconductor heterointerfaces monitored by pump-probe second-harmonic generation

We provide the evidence for the hot-LO-phonon-assisted absorption at semiconductor heterointerfaces. The process is demonstrated with $\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{Sb}$ interface when the photon energy is tuned below the band-gap energy for GaAs, but it is in a great excess for GaSb. The excitation of carriers in GaAs in the vicinity of the heterointerface is shown to be assisted by hot LO phonons generated in GaAs and GaSb within the relaxation of hot carriers in GaSb. The effect has been observed in the ultrafast pump-probe experiment through the interfacial-electric-field-induced second-harmonic generation response.

Figure 1

(Color online) (a) The schematic representation of the band alignment of the $\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{Sb}∕\mathrm{In}\mathrm{As}$ heterostructure. (b) The TIEFISHGC traces measured at the photon energy indicated are shown in black. Traces shown in red/gray are the difference of signals measured with $\hslash \omega >1.43\mathrm{eV}$ and that taken with $\hslash \omega =1.43\mathrm{eV}$. The individual trace baselines are arbitrarily shifted for better observation.

Figure 2

(Color online) (a) $\hslash \omega$-time mapping of the dc field at the $\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{Sb}$ interface. The IEFISHG intensity color/gray scale key is shown on the right. (b) The corresponding photon energy dependences extracted from (a) at the time delays indicated. The vertical dotted lines show the position of $E_g$ for GaAs and $E_g-\hslash {\omega }_{\mathrm{LO}}$.

Figure 3

(Color online) The difference of the TIEFISHGC traces taken with $\hslash \omega =1.45\mathrm{eV}$ and $\hslash {\omega }_{\mathrm{LO}}=1.43\mathrm{eV}$. The result of the fit is shown in red/gray. The fit components are shown in blue/dark gray.