The interaction of Hg0.72Cd0.28Te substrates with submonolayer-deposited films of Al and Ge has been investigated by ultraviolet photoelectron spectroscopy (UPS) using a sychrotron radiation source. The surfaces of the p-type samples were formed by cleaving in ultrahigh vacuum—a process which resulted in n-type surfaces. Very thin layers of Al(0.2–1 Å) were found to interact very strongly with the surface, causing a dramatic loss in the amount of Hg at the surface and a much smaller loss of Cd. As a result, the measured Cd/Hg concentration ratio increased by more than a factor of 2 for 1 Å of Al. At the same time, the valence-band features shifted downward in energy, reflecting an apparent change in the local band gap. In contrast, Ge was relatively inert with regard to the cleaved surface and caused little change in the substrate composition. The behavior of both deposited films can be predicted from the decreasing thermodynamic stability of Al2Te3, CdTe, HgTe, and GeTe and may be important to the formation of good Ohmic contacts.