Halogen vapor deposition of chalcogenide crystals: Lead sulfide

Abstract

n‐type single crystals of lead sulfide, PbS, have been grown by a novel chemical vapor deposition method of potential importance for growing a variety of chalcogenide crystals. A reduced‐pressure flowing system was developed based on the following chemical reactions: Pb+Cl₂→PbCl₂ and PbCl₂+H₂S→PbS+2HCl. Additional Cl₂ is used for fine control of the growth rate. The optimal growth conditions are a temperature of 650 to 750°C and a pressure of 8 Torr. Important to the furnace design is a quartz concentric gas injection arrangement which prevents premature mixing and reacting of the gases. n‐type single crystals of PbS having carrier concentrations of the order of 10¹⁹ cm⁻³ and Hall mobilities of 600 cm²/V sec at 300°K and as high as 14 000 cm²/V sec at 77°K have been grown. An isothermal anneal at 850°C for 15 days will convert the crystals to p type. Possible extensions of the technique to mixed lead‐tin salts, including tellurides and selenides, and to other chalcogenides are discussed.