The effect of short-term heat treatment on the thermoelectric properties of heavily doped n-type silicon germanium alloys

Hall effect and electrical resistivity measurements were carried out on samples of heavily doped n-type silicon germanium alloys during high temperature isothermal heat treatment*. The samples were initially annealed at 1300 K, quenched to room temperature and then subjected to short-term heat treatment at temperatures of 630 K, 825 K, 980 K and 1040 K. Dopant precipitates out of solution during the heat treatment. The rate of precipitation is fastest over the intermediate range of temperature and reaches a maximum around 750 K, at which temperature the carrier concentration falls by ~30 % in less than 30 min. This rapid precipitation of dopant significantly affects the thermoelectric properties and their temperature variations very much depend upon the experimental procedure employed in their measurement. The effect of dopant precipitation on the temperature variation of the electrical resistivity and Seebeck coefficient over the range 300 K to 1000 K is reported. It is concluded that comparison between thermoelectric data reported by different workers can only be made if the detailed temperature/time history of the sample is known.