We recently presented an approach to increase the SC in CVD, without using inhibitors or low temperatures and pressures. Instead, we proposed to add an inert gas with a higher molecular mass than the precursor molecules to promote the diffusion of lighter precursor molecules down a trench. We demonstrated our concept with improved SC in a CVD process to deposit B4C from B(C2H5)3 by adding Xe. Here, we test the same approach in an ALD process, using deposition of AlN from Al(CH3)3 (72 amu) and NH3 (17 amu), as precursors, with a co-flow of Kr (84 amu). We demonstrate how the addition of Kr can afford an ALD process with SC = 1.6 in a trench structure, but that the Kr addition does not lead to longer deposition depth in a lateral high aspect ratio structure.