Infrared transmission measurements of Bridgman grown AgGaSe2 chalcopyrite show a deleterious absorption peak centered at 9.3 mu m. The 9.3 mu m absorption was reduced by 63% using an additional post-growth heat treatment at 790 degrees C in a controlled partial pressure of selenium of 0.243 atm for 4000 min. A linear correlation was determined between infrared absorption and the selenium partial pressure during the heat treatments: alpha(9.3) (mu m) = -0.4048(P-se) atm(-1) cm(-1) +0.1322 cm(-1). A linear correlation was also determined between dark resistivity and 9.3 pm absorption coefficient: rho = -7 x 10(12)alpha(9.3 mu m)Omega cm(2) + 1 x 10(12)Omega cm. This correlation indicates that stoichiometric AgGaSe2 should have a dark resistivity of 10(12)Omega cm. These results support the identification of the 9.3 pm absorption defect as a native selenium vacancy. (C) 2008 Elsevier B.V. All rights reserved.