Beyond diffusion limit defect imaging and independent determination of the spatial profiles of electron and hole density near a dislocation defect by combining Raman and photoluminescence (PL) imaging

Although a large carrier diffusion length (DL) indicates high material quality, ironically it implies more carrier depletion by an individual extended defect. It also obscures the spatial resolution (SR) in PL imaging, where the SR is dictated by the carrier DL rather than by the optical diffraction limit. Raman imaging of the LO phonon-plasmon (LOPP) coupled mode can be used to recover the intrinsic SR of the optical system [1], as demonstrated by Raman imaging of dislocation defects in GaAs, achieving a 10-fold improvement in SR. Furthermore, by combining Raman and PL imaging near a dislocation defect, we can independently determine the electron and hole spatial profile, radiative and nonradiative recombination rate, which has not been possible using other techniques. We find that in GaAs the dislocation defect tends to behavior as a hope trap: the defect only depletes the electrons in a short range, whereas the impact range of the defect is much larger in PL imaging. The mismatch in the electron and hole distribution implies the formation of a polarization field near the defect. The imbalance between the two charge distributions suggests the diffusion is non-ambipolar. [1] Hu et al., Light: Sci. & Appl. 7, 23 (2018).