PREFERENTIAL SPUTTERING OF INP - AN AES INVESTIGATION

AES was used to determine the surface composition of InP bombarded with 0.5 to 5 kev Ar+ ions. The (100), (110) and some vicinal planes were sputtered. On all of these surfaces the phosphorus atoms were preferentially sputtered leaving an indium-enriched surface. The equilibrium surface composition showed no dependence on the argon ion energy or on the crystal orientation. A dependence on the angle theta of incidence was observed. The following steady state surface compositions were obtained: theta = 18-degrees, InP0.68 +/- 0.07; theta = 40-degrees, InP0.67 +/- 0.07; theta = 42-degrees, InP0.78 +/- 0.07; theta = 70-degrees, InP0.94 +/- 0.09. Our results are compared to other published measurements. There is a very large scatter between the results of different studies. This difference can be attributed to several factors. Predictions of several well-known preferential sputtering theories also exhibit large differences. These predictions show that the mass difference between the In and P atoms is the major factor contributing to the preferential sputtering of InP, with the surface binding energies of secondary importance. This conclusion is supported by Monte Carlo calculations using the TRIM-89 computer code.