81


four corners by an emitter diffusion (see Appendix A). The resistivity is calculated from [71]


           Trw V                                                  (3
           Xn2 1                                                  (6.3)


where w is the thickness of the chip, and V is the voltage difference between nearest neighbor contacts for a current, I, passed between the remaining two contacts. The TO-5 header was mounted in the sample holder of an Air Products and Chemicals AC-3L CRYO-TIP liquid nitrogen system. This enabled variation of the sample temperature between 100 and 350 K. The temperature was measured by a chromel vs gold with 0.07 atomic percent iron thermocouple. For temperatures above 350 K, the sample was placed in a Stratham Temperature Test Chamber.

     The structure used for the Hall coefficient measurements is the collector Hall effect resistor. The Hall coefficient is calculated from

            V HW
       RH  -                                                      . (6.4)


where VH is the voltage difference measured between opposite contacts for a current, I, passed between the remaining two contacts, and B is the magnetic field density perpendicular to the plane of the chip; thus the samples are oriented so that the magnetic field is in the crystal growth direction, <111> for the gallium-doped samples, and <100> for the indium-doped samples. The Hall mobility is determined from