four probe

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TO DETERMINE THE BAND GAP OF GERMANIUM CRYSTAL BY FOUR PROBE METHOD:

TO DETERMINE THE BAND GAP OF GERMANIUM CRYSTAL BY FOUR PROBE METHOD Apparatus Required *Four probe device *Germanium crystal *Heating Plate *Thermometer Construction Probes arrangement : The four spring loaded probes are collinear & equally spaced using teflon spacer. Probes are mounted over teflon bush for electrical insulation. The stand serves as a lid of oven & for correct measurement of temperature Oven : The oven is used for fast heating & cooling rates, enhancing the effectiveness for high quality heating.

WORKING FORMULA :

WORKING FORMULA The energy band gap of a Germanium crystal ( Ge ) is OBSERVATIONS Determination of resistivity & temperature S. No. Temperature T (°C) Voltage V (Volt) ρ (ohm-cm) 10^3/T Log ρ

The Physics Beyond…:

The Physics Beyond… Distance between probes, s=2 mm Thickness of crystal, W=0.066 cm Standard Value of E g = 0.67 eV Correction factor for non-conducting bottom surface Resistivity of Ge crystal as a function of inverse Temperature

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