Study of adsorption and nucleation of cadmium of germanium single crystals by a molecular beam technique

• Published in: Journal of crystal growth 1972-05, Vol.13-14, p.167-173
• Main Authors: Voorhoeve, R.J.H, Wagner, R.S, Carides, J.N
• Format: Article
• Language: English
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/0022-0248(72)90149-2

A molecular beam mass-spectrometric ultra-high vacuum technique was used for the study of adsorption and nucleation of cadmium on the (111), (211), (110) and (331) faces of 45 Ω-cm germanium single crystals. Extensive cadmium adsorption preceded nucleation on all these faces. On the (111) face, two adsorption states, with heats of adsorption of 25 and 27 kcal/mole were identified, illustrating the barrier for nucleation of bulk cadmium which has a sublimation energy of 26.9 kcal/mole. The critical supersaturation for nucleation, α∗ is found to be related to the atomic roughness of the germanium crystal face, the highest α∗ being found on (111), the lowest on (110) and (331). No relation is found between the amount of preadsorbed cadmium and the critical supersaturation. This indicates that preadsorption fills adsorption traps in which cadmium atoms are immobile and unable to participate in statistical clustering. The effect of electrically active impurities on the nucleation has been investigated for the (111) faces of germanium crystals doped with gallium or arsenic. Both types of dopants enhance nucleation, though only to a small extent.