Modulation above Pump Beam Energy in Photoreflectance

Figure 1

Schematic representation of critical points (CPs) E₀, E₀ + Δ₀ (indicated as E_SO), and E₁ of GaAs represented in ascending energy on the same energy axis of a typical experimental PR spectrum (left). The band diagram picture (right) illustrates the modulation mechanism at CPs, namely, periodic SPV generation, upon illumination with a chopped pump beam of energy slightly above E, inducing transitions at the fundamental gap. Notice that, although the E₀ + Δ₀ transition involves a valence state below the valence band edge (reference at zero energy), the corresponding energy is greater than the fundamental gap E.