Doping profile measurements from avalanche space−charge resistance: A new technique

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Abstract
A new technique, resistance−current (R−I) profiling, is described in detail. The method utilizes measurements of the isothermal space−charge resistance of an avalanching semiconductor junction to determine the doping concentration as a function of depth. The technique extends profiling capability beyond the depth limit of the usual capacitance−voltage (C−V) methods and is thus particularly useful in measuring epitaxial layers which are not ’’punched through’’ at breakdown. In addition, comparison of the R−I profile with the C−V profile allows the effective avalanche area (Aeff) of the junction to be determined. An analysis of the technique is presented based on the ’’two−zone’’ model, which has uniquely defined avalanche and drift zones. This model is justified by comparison with results from a full simulation of the dc I−V characteristics of abrupt−junction avalanche diodes. Techniques for measurement of R are then discussed. Finally, measurement results of typical GaAs−Pt IMPATT diodes are presented. Effective areas as low as one−third of the geometric area are observed in some devices. Measurements of Aeff as a function of diode diameter are shown to be consistent with a model in which breakdown occurs near the outer edge of the diode in an annular region of constant width.