Surface passivation of germanium by atomic layer deposited Al2O3 nanolayers

Surfaces of semiconductors are notorious for the presence of electronic defects such that passivation approaches are required for optimal performance of (opto)electronic devices. For Ge, thin films of Al2O3 prepared by atomic layer deposition (ALD) can induce surface passivation; however, no extensive study on the effect of the Al2O3 process parameters has been reported. In this work we have investigated the influence of the Al2O3 thickness (1-44 nm), substrate temperature (50-350 degrees C), and post-deposition anneal (in N-2, up to 600 degrees C). We demonstrated that an effective surface recombination velocity as low as 170 cm s(-1) can be achieved. The role of the GeOx interlayer as well as the presence of interface charges was addressed and a fixed charge density Qf= -(1.8 +/- 0.5) x 10(12) cm(-2) has been found. The similarities and differences between the passivation of Ge and Si surfaces by ALD -Al2O3 prepared under the same conditions are discussed.