Impurity conduction and negative magnetoresistance in compensated n type indium phosphide,at low temperature

Electrical resistivity, mobility, magnetoresistance in compensated n type InP with a carrier density n = 7,2 10¹⁶/cm³ have been measured in the temperature range 1,7 K – 100 K, in magnetic fields up to 0,9 Tesla. Under a temperature T_C, which corresponds to the formation of an impurity band in which the electron conduction is metallic, the magnetoresistance becomes negative. Longitudinal and transverse magnetoresistances have similar behaviours. Longitudinal magnetoresistance which is treated here, has the behaviour of a system of paramagnetic spins for which the Curie point is determined. The variation of the negative magnetoresistance versus magnetic field and temperature is quite well approximated by a Langevin function L(u) with $\text{u}\text{=}\text{μ}{}^1\text{B}\text{kT}$; $\text{μ}{}^1\text{=}\text{n}\text{μ}{}_{\mathrm{<mtext>B</mtext>}}$ is the effective magnetic moment where μ_B is the Bohr magneton and n = 5. The value of the effective magnetic moment and the average separation of donors, allow the discussion of the negative magnetoresistance on the basis of the Toyozawa model. Other models are discussed and it seems that in the range of impurity concentrations concerned, the picture of localised moments is more consistant that a “mobility edge” model.