The diffusion of Ga in monocrystalline epitaxial layers on GaAs was measured as a function of the Cu/In ratio (table 8). Some Ga was introduced by the substrate. The Ga concentration profiles were measured by means of secondary ion mass spectrometry, and were analyzed by performing numerical solutions of Fick’s second law which took account of motion of the surface and of Ga desorption. All of the films had Cu/(In+Ga) ratios that were greater than unity, and the Cu/In ratio was controlled by the deposition conditions. It was found that the Ga diffusivity exhibited a minimum near to a Cu/In ratio of unity, and increased rapidly for deviations in either direction. The diffusivity ranged from a minimum value of 2.7 x 10-13cm2/s when Cu/In was equal to 0.94, to 5 x 10-11cm2/s when Cu/In was equal to 1.41 and to 7 x 10-12cm2/s when Cu/In was equal to 0.43. It was concluded that Ga diffused via metal vacancies on the Cu or In sub-lattices.

D.J.Schroeder, G.D.Berry, A.A.Rockett: Applied Physics Letters, 1996, 69[26], 4068-70

Table 8

Diffusivity of Ga in CuInSe2