Asymmetric Doping‐Dependent Electron Transport Mobility in InxGa1–xAs/GaAs Quantum Well Field‐Effect Transistor Structure

We analyze the asymmetric doping‐dependent electron mobility μ of GaAs/InGaAs/GaAs quantum well field‐effect transistor (QWFET) structure. We consider doping concentrations, nd1 and nd2, in the substrate and surface barriers, respectively, and study μ as a function of nd2, taking (nd1 + nd2) unchanged. An increase in nd2 decreases nd1, yielding interesting changes in the occupation of subbands. For well width W < 164 Å, μ is due to single subband occupancy (SSO). Around W = 164 Å, there occurs first SSO, then double subband occupancy (DSO), and again SSO with an increase in nd2. Near the transition of subbands, abrupt discontinuities in μ arise due to inter‐subband effects. Thus, high to low and then high values of μ are obtained, displaying almost flat‐like variations, symmetric about |nd2 − nd1| = 0. As W becomes wider, complete DSO occurs throughout the range of nd2 having reduced μ. Alternatively, keeping nd1 unchanged and by increasing nd2, μ raises due to enhanced N s , with a drop near the transition from SSO to DSO. Under SSO, μ is controlled by the ionized impurity and alloy disorder scatterings, while under DSO, the impurity scattering determines μ. Our analysis on μ can help to examine the inter‐subband effects on device characteristics of the QWFET system.