Intervalley transitions in inversion layers

Abstract

Transitions between sub‐band systems deriving from valleys with different effective mass in the direction of surface quantization involve large momentum transfer. As a consequence the probabilities for impurity‐induced transitions between the respective sub‐band systems are low. The corresponding transitions by phonon emission are energetically forbidden if the sub‐band splitting does not exceed the energy of acoustic phonons near the zone boundary. The transfer of carriers into a sub‐band system with lower mobility provides an explanation of the experimentally observed negative photoconductivity and of the extremely long photoresponse times in n‐type Si<100≳ inversion layers. The dependence of the photoconductive response on the band splitting provides information about the relative position of the electric sub‐bands in different sub‐band systems. Relaxation losses from transitions between different sub‐band systems also imply a possibility for measuring the sub‐band energies if the system is no longer in the electric quantum limit.