The use of a rectangular current pulse for tracing semiconductor resistivity profiles†

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Abstract
A technique is described for displaying on an oscilloscope the inverse doping profile, n0 −1(x), of a semiconductor material. A blocking contact is made to the material to form a diode that is placed in the feedback path of a specially constructed wide-baud integrator. The integrator action forces a rectangular pulse of current, typically 10 microamps in height and 100 microseconds long, into the contact in the reverse direction. The first differential of the voltage developed across the diode is proportional to the depth, x:, and is used to deflect an oscilloscope beam in the ‘X’ coordinate ; the second differential is proportional to the inverse doping level, and is used to deflect the beam in the ‘Y’ direction, thus displaying n0 −1(x). Besides evaporated-metal and junction (p+−n) structures, Mercury has been successfully employed as a contact, and has the advantage of being movable. Results for two GaAs wafers are compared with measurements from an automated C(V) plotter, with good agreement. The fact that the method is rapid might commend it to production application where material assessment is normally desirable.