Capacitance-Voltage Profiling of Multilayer Semiconductor Structures

Abstract

C-V profiling has traditionally found its importance in the determination of semiconductor doping profiles and, more recently, to provide estimates of heterojunction band offsets [1]. It has been recognised [2] that a profile of the free electron concentration n(x) is obtained from C-V techniques rather than that of the doping profile N_d(x). These are not necessarily the same even for the case of very shallow donors. Indeed, they will be different whenever the measured electron concentration is not uniform. It has also been shown [3] that C-V profiling viewed as a measurement of the free carrier concentration is itself inexact if n(x) varies appreciably over a distance less than a Debye length. The measured apparent carrier concentration ñ(x) then differs from both n(x) and N_d(x). There is also still some uncertainty in the use of C-V profiling to determine heterojunction band offsets due to the effects of a finite donor depth [4] and of interfacial charge distributions [5].