Istituto dei materiali per l'elettronica ed il magnetismo     
Attolini G., Bosi M., Calicchio M., Ferrari C., Frigeri C., Vad K., Csik A., Zolnai Z. Interdiffusion study in MOVPE grown Ge/GaAs and GaAs/Ge heterojunctions. In: EW-MOVPE XIII (Ulm, Germania, 8-10/6 2009). Proceedings, article n. D3. EW-MOVPE XIII, 2009.
GaAs/Ge heterostructures are widely used for solar cell applications: multiple junction cells, consisting of dual junctions InGaP/GaAs/GaAs or GaAs/Ge and triple junctions InGaP/GaAs/Ge are continuously improving their efficiency. Sharp heterointerfaces and abrupt dopant profiles are essential to realize this kind of devices. One major problem with the Ge and GaAs heterointerface is the interdiffusion of the elements in the layer, i.e. Ge in GaAs and Ga and As in Ge. Since Ge is a dopant in GaAs, the diffusion of Ge into the GaAs increases the carrier concentrations in the GaAs layer; in addition the diffusion of Ga and As into Ge makes the doping control of the Ge epilayers problematic. Here we report on the study of the diffusion of Ge, As and Ga in Ge/GaAs and GaAs/Ge heterojunctions grown by metal-organic vapor phase epitaxy using iso-butylgermane, arsine and trimetilgallium in hydrogen atmosphere at low pressure. Secondary Neutral Mass Spectrometry, High Resolution X-ray Diffraction, Transmission Electron Microscopy, have been used to investigate the samples. We found different diffusivity of the atoms (Ga, As, Ge) when the sequence of the grown layers changes and we analyze the diffusion difference between substrates and films, and between the two epitaxial layers.
Subject Germanium

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