Precision assessment of carrier concentration in semiconductors with negative electron affinity

Narrow bandgap n-InAs and several other semiconductors possess negative electron affinity. This causes serious problems while assessing free charge carrier concentration by electrical methods. Particularly, in conventional capacitance–voltage (C–V) measurements, we registered the overestimated (by several degrees) apparent carrier concentration as a result of the near-surface layer enrichment with electrons. This issue is thoroughly discussed and analyzed in this paper. Three approaches for adequate processing of C–V measurements to eliminate the considered influence of the electron-enriched surface on measured capacitance were elaborated for correct and reliable estimation of free charge carrier concentration. A novel technique combining electrochemical capacitance–voltage measurements in nonequilibrium conditions is presented. The experiment is accompanied by the numerical solution of the Poisson equation using the modified Thomas–Fermi approximation.