Abstract: A magnetic sensor, memory, and magnetic imager has been described for sensing a magnetic field in two directions concurrently incorporating a bar of semiconductor material having a rectangular cross-section, electrodes for introducing current along the length of the semiconductor material, and electrodes positioned on respective corners of the rectangular cross-section at a common distance along the current path whereby the Hall voltage may be detected concurrently in two directions. The memory includes the above magnetic sensor plus a disk having a magnetic layer thereon for storing information, a positioner for moving the disk, a memory control circuit and a signal processor circuit. The magnetic imager includes a plurality of magnetic field sensors positioned in a one or two-dimensional array. The invention overcomes the problem of mapping magnetic fields with high spatial resolution with high magnetic sensitivity in two directions concurrently.

Abstract: A strained In.sub.y Ga.sub.l-y As layer is employed in a GaAs/Al.sub.x Ga.sub.l-x As transistor. Since the bandgap of In.sub.y Ga.sub.l-y As is much smaller than that of GaAs, there is no need for a troublesome large-mole-fraction of aluminum in the Al.sub.x Ga.sub.l-x As layer in order to maintain a large bandgap discontinuity. This and other advantages of the structure set forth result in devices having improved operating characteristics.