W~x      2 2   AV-                                           (6.6)
               ec A2 AC2'


where AV is an incremental, change in the gate voltage, and the measured capacitance is due to both the oxide and the semiconductor.   A selfconsistent check was made on the measurements of collector dopant density by using the base-collector diode. This structure (see Appendix A) consists of. a base diffused into a collector and a metal field plate to control the periphery. The field plate. overlaps both the base and a diffused emitter, channel stop which also serves as topside collector [68]. To obtain a correct density profile the field plate is biased at the flat-band potential [74]. Capacitance-voltage measurements were

taken with a Princeton Applied Research 410 C-v Plotter and a Hewlett

*Packard 7010A X-Y Recorder.

      From each silicon wafer, eight four-probe resistors, eight Hall resistors, and eight capacitor-diode chips were selected for encapsulati-on. These were' chosen on the basis of low leakage Currents and good contacts at the metal bonding pads. Measurements were made on each of the devices and data from the five to eight devices closest to the mean value of the measurements were then averaged. In this manner we arrived at representative values of resistivity, Hall coefficient, and dopant density for each sample. The results of these measurements and comparisons wit h the theory of.Chapters III through V are presented in the next chapter.