Quantum Wells*

Many semiconductors exhibit persistent photoconductance, whereby light induces long-term changes of conductance. Generally, this phenomenon entails carrier accumulation, while occasionally it can lead to depletion. Yet, a simultaneous control of accumulation and depletion by optical means has remained elusive. Here, we present the quantum well at the LaAlO₃/SrTiO₃ interface, where in addition to accumulation, a secondary photoexcitation enables carrier depletion. The balance between both processes is wavelength dependent, and allows tunable accumulation or depletion in an asymmetric manner, depending on the relative arrival time of photons of different frequencies. The role played by time in this unconventional photoresponse paves the way to an optical implementation of spike-timing dependent plasticity. Interesting, it may also open the way to an optical control of amplitude and sign of the spin-charge conversion efficiency in LaAlO₃/SrTiO₃ quantum wells.
[1] Y. Chen et al., Physical Review Letters, 124 246804 (2020).
[2] Y. Chen et al., ACS Appl. Electron. Mater., 1 1189 (2019).