HEAT TREATMENT OF FE-DOPED INP SUBSTRATES FOR THE GROWTH OF HIGHER PURITY GA//0 //. //4 //7 IN//0 //. //5 //3 AS BY MBE.
Impurity outdiffusion, in particular Fe, Mn, and Cr, from Fe-doped InP into GaInAs epitaxial layers during molecular beam epitaxy growth can account for as much as two-thirds of the carrier concentration and can reduce electron mobilities by as much as 40%. By heating the InP before growth and then polishing to remove the impurities which have been gettered at the surface, epitaxial layers with unintentional carrier concentrations less sensitive to substrate temperature and higher mobilities can be obtained. Fe-doped InP has been annealed under pure H//2 , a 92% Ar-8% H//2 mixture, and a PH//3 ambient to relate the efficiency of impurity gettering to the ambient heating. Hall measurements show that the carrier mobilities in epitaxial layers grown on InP annealed in a pure H//2 ambient increase more than in those layers grown on InP heated in an Ar-H//2 mixture. This suggests that the formation of phosphorus vacancies aids the surface gettering of outdiffusing impurities.
