Use of spatially dependent electron capture to profile deep-level densities in Schottky barriers

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Abstract
A new procedure to profile deep-level densities within the space-charge region of Schottky barriers is presented. The method takes advantage of the spatial dependence of the time constant for the free-electron capture by deep-donor traps. The amplitude of the slow component of the capture capacitance transient following a negative reverse voltage pulse is simply related to the trap density at the point where the Fermi level crosses the trap level itself. The density profile of a given trap can be achieved by measuring the slow-component transient signal as a function of the reverse voltage at a suitably chosen constant temperature. The estimated spatial resolution of the method was near 50 Å in a practical case. Experimental density profiles for EL14, EL8, EL3, and the EC−ET =0.37 eV level in Cr/GaAs and Al/GaAs Schottky barriers are presented and discussed. The procedure is expected to be also applicable to the case of trap densities comparable with the shallow-donor density without introducing large errors.