SEMICONDUCTOR DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a highly reliable semiconductor device including an oxide semiconductor.SOLUTION: The semiconductor device includes a laminate structure including an oxide semiconductor layer and an insulating layer which is in contact with the oxide semiconductor layer. The oxide semiconductor layer comprises: a first layer in which a channel is formed; and a second layer which is provided between the first layer and the insulating layer. The energy at the bottom of the conduction band in the second layer is closer to a vacuum level than that in the first layer. The second layer functions as a barrier layer which prevents a defect level from being formed between the insulating layer in contact with the oxide semiconductor layer and the channel. The first and second layers each have an ultrafine crystal portion in such an extent that no periodicity is observed in an atomic arrangement macroscopically or no long-distance order is observed macroscopically. For example, the layers have a crystal portion in which a periodicity is observed in the atomic arrangement in the range of 1 nm or more and 10 nm or less.