MEASUREMENT OF BAND OFFSETS AND INTERFACE CHARGES BY THE C-V MATCHINGMETHOD

The present article describes a novel application of capacitance-volta ge measurements to determine simultaneously the band discontinuities ( Delta E-V, Delta E-C) and interface charge density (sigma) of heteroju nctions. The method, which we refer to as C-V matching, complements th e most versatile C-V profiling technique proposed by Kroemer and succe ssfully applied by others. In contrast to the C-V profiling which is l imited to isotype heterojunctions, the new method is applicable to p-n heterojunctions as well. The methodology is based on three cardinal e quations which are not controversial-the lineup of the bands relative to the common Fermi level (at equilibrium) or the quasi-Fermi levels ( when voltage is applied), the charge neutrality and the expression for the total capacitance of the heterostructure. The three equations are formulated for equilibrium as well as nonequilibrium conditions, usin g quasi-Fermi bevels and the quasi-equilibrium approximation. The thre e cardinal equations are defined by the two constant (albeit unknown) interface parameters (Delta E-V, sigma) which are assumed to be indepe ndent of the voltage and two variables (phi(s1), phi(s2)), which descr ibe the total band bending on each side of the heterointerface and var y with the applied voltage. The actual interface parameters Delta E-V, sigma are determined by C-V matching between the calculated and the m easured curve. The metric for the optimal match between calculated and measured capacitance vectors is discussed. The methodology presented in this study is general and can be applied to semiconductor-semicondu ctor and semimetal-semiconductor heterojunctions. It is illustrated he re for the HgTe-CdTe semimetal-semiconductor heterojunction, which can not be evaluated by the C-V profiling. The significance of the simulta neous determination of the band discontinuities and interface charges of heterojunctions is also discussed. In addition, the methodology pre sented in this article models the behavior of biased heterojunctions u nder nonequilibrium conditions, taking into consideration the values o f band offset and interface charge density of an actual heterointerfac e. (C) 1998 American Institute of Physics. [S0021-8979(98)08113-4].