Strain-induced exciton decomposition and anisotropic lifetime modulation in a GaAs micromechanical resonator

We demonstrate mechanical modulations of the exciton lifetime by using vibrational strain of a gallium arsenide (GaAs) resonator. The strain-induced modulations have anisotropic dependences on the crystal orientation, which reveals the origin of these modulations to be the piezoelectric effect. Numerical analyses based on the tunneling model clarify that the mechanical strain modulates the internal electric field and spatially separates the electrons and holes, leading to nonradiative exciton decomposition. This carrier separation also generates an optomechanical back-action force from the photon to the resonator. Therefore, these results indicate that the mechanical motion can be self-modulated by exciton decays, which enables one to control the thermal noise of the resonators and provides a photon-exciton-phonon interaction in solid-state systems.

Figure 1

(a) Schematic image of the mechanical resonator. (b) Band diagram of the resonator along [100]. The modulation-doped structure forms a potential gradient in GaAs. (c) Configuration of the time-resolved stroboscopic PL measurement. The PL spectra and their time evolution were measured with a CCD and APD, where the pump pulses were synchronized to the vibration. (d) PL spectrum of the GaAs-based resonator at equilibrium. The three peaks (red and blue) come from acceptor bound excitons in GaAs. The dashed line indicates the background signal. (e) Frequency response of the resonator as measured with a He:Ne laser and Doppler interferometer at 8 K at ${10}^{-5}\mathrm{Pa}$.

Figure 2

(a) Stroboscopic PL spectrum of the acceptor bound excitons in the resonator oriented to [0-11]. The vertical axis indicates the relative phase of the pump pulse to the mechanical motion. The inset shows the crystal orientation of the resonator. The dashed line is the fitted curve for the exciton energy. (b) Time evolution of the PL intensity at relative phases of 0 and π. (c), (d) Same as (a) and (b) but for the resonator oriented to [011]. The energy modulations occurred in the same phase, whereas the intensity and lifetime modulations occurred in the opposite phases between the two resonators.

Figure 3

(a) Energy diagram of an electron in a Coulomb potential of a hole and internal electric field. The electric field causes electron tunneling. (b) Exciton lifetimes and PL intensity calculated with the tunneling model. (c), (d) Experimental (circles) and calculated (solid lines) exciton lifetimes and PL intensity as a function of oscillation phase. The resonators were oriented to [0-11] (c) and [011] (d).

Figure 4

(a) Mechanical modulation of the back-action force via lifetime modulation in the resonator oriented to [0-11]. (b) Detuning energy dependences of force modulations by the deformation potential ($\nabla F_{DP}$) and piezoelectric effect ($\nabla F_{PE}$). The dashed line indicates the absorption spectrum of the exciton. (c) Linewidth dependences of the force modulations. $\nabla F_{PE}$ ($\nabla F_{DP}$) becomes dominant when the linewidth is wider (narrower) than 60 μeV.