EVIDENCE FOR THE COEXISTENCE OF 2-DIMENSIONAL AND 3-DIMENSIONAL ELECTRON GASES IN THE EMITTER OF DOUBLE-BARRIER DEVICES

We have analysed the dimensionality of the emitter electron gas of dou ble barrier devices (DBD) under bias and found evidence for the coexis tence of both two- and three-dimensional (2D and 3D) electron gases. M agnetotunneling measurements performed on a series of n-type GaAs/(AlG a)As DBD with varying emitter doping profiles have shown that the elec tron gas may have a 2D and/or 3D character depending on the emitter do ping level and on the applied bias. In devices with heavily doped emit ter layers, electrons tunnel from 3D-states, whereas for lightly doped emitters a 2D-electron gas is formed in the emitter contact. For inte rmediary doping levels both 2D- and 3D-electron gases may coexist, dep ending on the applied bias. (C) 1996 Academic Press Limited