Graded design of carrier concentration in PbTe by heat-treatment

In order to develop a new process of forming a carrier concentration gradient in lead telluride PbTe only by using heat-treatment, the effect of heat-treatment on a carrier concentration n of the p-type PbTe has been investigated, and the p-type PbTe has been heat-treated using a temperature gradient. The as-grown stoichiometric PbTe was p-type with an n of 1.0 x 1024m-3. Vacuum thermal exposure with Te-rich PbTe at 900 K for 1 h increased the n of the stoichiometric PbTe to 5.1 x 1024m-3, which indicates that hole formation was achieved by thermal exposure at this temperature and duration. The thermally exposed stoichiometric PbTe was heat-treated in the temperature range of 400 to 900 K for a period of 24 h. The n decreased with an increasing heat-treatment temperature of between 300 and 500 K, while the n increased with an increasing heat-treatment temperature of between 500 and 900 K. A minimum n was measured at 500 K, above which the formation energy of holes was determined to be 16.4 kJ/mol. On the basis of these results, a 19 mm long thermally exposed stoichiometric PbTe was heat-treated using a temperature gradient of 340-900 K for a period of 24 h. A continuous change in n was formed in the PbTe, and a minimum value of n was determined to be at a position corresponding to the heat-treatment temperature of 500 K. A continuous gradient of hole production was successfully achieved in the p-type PbTe only by heat-treatment using a temperature gradient. (orig.)