GB1014829A - Arrangements for measuring electrical properties of semiconductors - Google Patents

Abstract

1,014,829. Measuring electrical properties of semi-conductors. TEPAS INSTRUMENTS Inc. Sept. 24,1962 [Oct. 2, 1961], No. 36236/62. Heading G1U. An apparatus for measuring electrical properties of a semi-conductor comprises an impedance bridge which responds to the impedance of the semi-conductor, which is connected thereto,an arrangement for balancing the bridge when the semi-conductor is at a first reference temperature, and an arrangement for heating the semi-conductor to a second higher temperature to rebalance the bridge, the bridge being unbalanced between the first and second temperatures. Measurement of this second temperature yields information concerning the resistivity or impurity concentration of the semi-conductor. The resistivity of semi-conductor materials rises to a maximum at a particular temperature and then falls again with increasing temperature, the maximum resistivity and the temperature of occurrence thereof depending on the particular semi-conductor and impurity concentration therein. The temperature range from a reference temperture where the semi-conductor has a measured resistivity to the higher temperature where it has the same resistivity is also specific to a particular semi-conductor impurity combination, and a measurement of this range is used in the determination of an unknown resistivity. The semi-conductor 48 (Fig. 5) is mounted in a temperature chamber 40 with a thermocouple 50 positioned therein. The output from the thermocouple is fed to a temperature indicating instrument 56. The semi-conductor is connected in one arm of an A. C. bridge 44, the output of which is fed to an oscilloscope 46. The arrangement is calibrated by using several wafers of P-types germanium with different impurity concentrations and of known resistivity at a reference temperature. These are used in the apparatus in turn, the temperature of the enclosure 40 being adjusted to the reference temperature as shown on the indicator 56. The A.C. bridge is then adjusted until a balance is shown on the oscilloscope 46. This may conveniently be done by arranging that the oscilloscope displays a trace which is horizontal at balance, but inclined when out of balance, the direction of the inclination indicating the phase of the imbalance. The temperature of the enclosure is then raised until the bridge returns to balance, the temperature at which this occurs being noted. A curve is plotted for the several calibrating wafers, showing the resistivity at the reference temperature against the elevated temperature at which the resistivity returns to the same value. The procedure outlined above is then applied to an unknown sample and the rebalance temperature noted. The corresponding resistivity can then be read from the curve. The resistivity cannot be directly determined from the balance components of the A.C. bridge, since several unknown fixed resistances, such as the resistance of the semi-conductor mount, are in series with the semi-conductor resistance.