Al₂O₃ Passivation Effect in HfO₂·Al₂O₃ Laminate Structures Grown on InP Substrates

The passivation effect of an Al₂O₃ layer on the electrical properties was investigated in HfO₂-Al₂O₃ laminate structures grown on indium phosphide (InP) substrate by atomic-layer deposition. The chemical state obtained using high-resolution X-ray photoelectron spectroscopy showed that interfacial reactions were dependent on the presence of the Al₂O₃ passivation layer and its sequence in the HfO₂-Al₂O₃ laminate structures. Because of the interfacial reaction, the Al₂O₃/HfO₂/Al₂O₃ structure showed the best electrical characteristics. The top Al₂O₃ layer suppressed the interdiffusion of oxidizing species into the HfO₂ films, whereas the bottom Al₂O₃ layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was more effectively suppressed in the Al₂O₃/HfO₂/Al₂O₃/InP structure than that in the HfO₂-on-InP system. Moreover, conductance data revealed that the Al₂O₃ layer on InP reduces the midgap traps to 2.6 × 10¹² eV^-1 cm^-2 (compared to that of HfO₂/InP, that is, 5.4 × 10¹² eV^-1 cm^-2). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers.