Concentration of electrons in selectively doped GaAlAs/GaAs heterojunction and its dependence on spacer-layer thickness and gate electric field

Abstract

The concentration N_s of two‐dimensional electrons in N‐GaAlAs/GaAs systems is studied; N_s shows a systematic decrease when the thickness W_sp of an undoped GaAlAs ‘‘spacer layer’’ is increased. Such a dependence is shown to be well explained by the theory in which the size quantization is taken into account. Furthermore, N_s is studied as a function of gate voltage in field‐effect transistor (FET) structures and found to saturate once N_s reaches its limiting value. This phenomenon is strongly dependent on W_sp and is well ascribed to the formation of nondepleted region in the GaAlAs layers. Implications for FET designs are discussed.