Heterojunction tunnel structures as devices

Semiconductor multilayer structures which contain ultra-thin tunnel barriers have been used to produce a wide variety of prototype devices with very attractive figures of merit. Some of the remaining problems that have prevented commercialisation are discussed. These problems also challenge mainstream silicon microelectronics, and some further novel structures are described that might allow a degree of integration perpendicular to the wafer surface. In particular it is possible to ion implant through tunnel structures to modify the properties of deeper layers, and yet restore the pristine electronic properties by annealing. Tunnelling must be tamed if the momentum of the microelectronic revolution is to be maintained for more than another 10 years