Influence of intervalley transitions on the photoconductivity in n-type Si 〈100〉 inversion layers

Transitions between the different sub-band systems corresponding to the valleys with low and high 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 K-point. Negative photoconductivity due to carrier transfer into the sub-band system with lower mobility and extremely long response times, as observed experimentally,¹ results if the sub-band splitting is less than this energy. Photoconductivity effects in 〈100〉 inversion layers will be weaker and response times will be much shorter for sub-band splitting larger than the critical value. For the corresponding case in 〈100〉 inversion layers, in contrast, strongly enhanced photoresponse is expected and the long response time should persist.