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Measurement of Hall voltage and resistivity Measurement of Sheet Resistivity Measurement of Hall voltage V43 V14 RA sheet F (Q ) where Q 2 ln 2 I12 I 23 RB Resistivity sheet t Here, t = thickness of the sample n sheet sheet 1 q q sheet Slide # 1 Variation of F with Q F(Q) = 1, if RA = RB Slide # 2 Summary of the Hall measurement • For Hall measurements the magnitude of the magnetic field should be small to avoid magneto-resistance or reduction in conductance due to the magnetic field • Measurement of both mobility and sheet charge density is possible • The volume density of carriers is possible to estimate if the thickness of the sample is known • The sign of the charge carriers can be found from the sign of the Hall voltage • Advantageous for samples having 2DEG since direct measurement of sheet charge density can be made unlike CV technique • Hall measurement includes overall effects of both majority and minority carriers Slide # 3 Hall Effect sensor: Chip and Spec ANALOG DEVICES - AD22151YRZ IC, HALL EFFECT SENSOR, LINEAR, 8-SOIC Slide # 4 Scattering processes in bulk GaAs • • • • • Ionized impurity scattering Acoustic phonon scattering Polar optical scattering Alloy scattering Defect related scattering Note that ionized impurity scattering is extremely important, and dominates all other for higher doping concentrations Matthiessen rule for total mobility calculation: 1 i 1 i Slide # 5