Field effect transistor

摘要

An insulating film is provided over one surface of a first semiconductor layer including a first oxide semiconductor including indium as a main component, and a second semiconductor layer including an i-type second oxide semiconductor is provided in contact with the other surface. The energy difference between a vacuum level and a Fermi level in the second oxide semiconductor is larger than that in the first oxide semiconductor. In the first semiconductor layer, a region in the vicinity of the junction surface with the second oxide semiconductor which satisfies the above condition is a region having an extremely low carrier concentration (a quasi-i-type region). By using the region as a channel, the off-state current can be reduced. Further, a drain current of the FET flows through the first oxide semiconductor having a high mobility; accordingly, a large amount of current can be extracted.

主权项

1. A field effect transistor comprising:
a first semiconductor layer including a first oxide semiconductor, wherein the first oxide semiconductor includes indium and gallium, and wherein a percentage of indium to all elements other than oxygen is 50 at. % or more in the first oxide semiconductor; a second semiconductor layer in contact with a first surface of the first semiconductor layer, wherein the second semiconductor layer includes a second oxide semiconductor, wherein the second oxide semiconductor is an i-type oxide semiconductor, wherein the second oxide semiconductor includes gallium and indium, wherein a percentage of gallium to all elements other than oxygen is 50 at. % or more in the second oxide semiconductor, and wherein a bandgap of the second oxide semiconductor is wider than a bandgap of the first oxide semiconductor; a conductive layer adjacent to a second surface of the first semiconductor layer; a first insulating film between the conductive layer and the first semiconductor layer; a pair of first doped regions with the first oxide semiconductor therebetween; a pair of second doped regions with the second oxide semiconductor therebetween, one of the pair of second doped regions and one of the pair of first doped regions being stacked, and the other of the pair of second doped regions and the other of the pair of first doped regions being stacked; a first electrode in direct physical contact with the one of the pair of first doped regions and the one of the pair of second doped regions; and a second electrode in direct physical contact with the other of the pair of first doped regions and the other of the pair of second doped regions, wherein an energy difference between a vacuum level of the second oxide semiconductor and a Fermi level of the second oxide semiconductor is larger than an energy difference between a vacuum level of the first oxide semiconductor and a Fermi level of the first oxide semiconductor.