The lack of adsorption onto InN can be explained by the low reactivity of ammonia onto the surface. At temperatures above 320 K at CVD and ALD pressures even the most stable termination, NH2(tp), is less thermodynamically stable than ammonia in gas phase at normal pressures and bare In sites. According to the HSAB theory In is, compared to Al and Ga, a soft acid while the nitrogen in ammonia is a hard base . As hard bases prefer to react with hard acids and soft bases prefer soft acids, ammonia would prefer to react with the harder acid Al or Ga than with In. This is also shown in the ratio of NH3 to 13-precursor used in CVD of 13Ns,