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The factor relating the Hall cocfficient to carrier concentration has been determined in n-type silicon by combining optical measurements of the carrier concentration at infrared frequencies with conventional dc Hall effect measurements. Interpreting this factor in terms of electronic charge, mobility anisotropy and the usual scattering constant, the latter is found to reach values much greater than unity, especially a t 77 OK, when with a doping level of 2.6 x 1017 0111-3 a value of 7.3 is obtained. IntrodiictionThe purpose of this short papcr is to communicate new experimental values for the Hall scattering constant in n-type silicon. It is found to be particularly large a t 77 O K for specimens dopcd = 1018 ~m -~.A recent paper [l] by the authors showed how, in semiconductors, thc concentration and effective mass of conduction band electrons can be determined from measurements of the infrared free carrier Faraday effect and dispersion. I n fact, observation of these t w o phenomena yields values of m2 Nlm; and m Nlm,, respectively, where N is the carrier concentration, mF and mR arc relevant effective mass parameters, and m is the electron mass. For multivalley conduction band states, such as those pertaining to silicon, Here mL and mT are the longitudinal and transverse effective masses corresponding to the ellipsoidal energy surfaces. Values obtained for N and mT in this way are not sensitive to R since it is large. Actually K has been taken to bc 4.3, the room-temperature value deduced from experimental observations of the stress dependence of Faraday rotation [2]. This is close to that found from low-temperature cyclotron resonance experiments [3].It is prudent to observe both the Paraday effect and dispersion to find N a t room temperature because the effective mass has not been measured by an independent experiment a t such a high temperature. At low temperatures (c.g., 77 OK), however, it is only necessary to observe the Faraday rotation since m, can be calculated from the accurate cyclotron resonance data available.11 pliysica (b) 4R/l