Hot-carrier dynamics and transport in III V heterostructures for photovoltaic applications

Type-II multiple quantum well superlattices based on InAs/AlAsSb are investigated for ground- and excited-state charge carrier transport and excited-state charge carrier dynamics. It is found that ground-state transport matches well to impurity and optical phonon interactions, while the excited-state transport shows increased terahertz photoconductivity for the correct excitation conditions that have previously been linked to a metastability in the early time response after photoexcitation. This regime also shows a reduction in carrier mobility, which is also expected to be due to ambipolar diffusion and increased carrier carrier scattering. Overall, carrier excited-state dynamics confirm the metastability in early time response and are related to strong Auger scattering. For increased excitation intensities, the Auger-scattering rate increases to obtain a lower carrier density more rapidly. The result is a stronger scattering of carriers energetically deeper into their respective bands, where they exhibit a much slower carrier recombination rate and can maintain their relative temperature as a result of a phonon bottleneck that forces reabsorption of optical phonons. In addition to a previously reported phonon bottleneck, the carrier dynamics offer potential pathways to stabilize hot carriers with further bandgap engineering.