AlO Passivation Effect in HfO·AlO Laminate Structures Grown on InP Substrates.

The passivation effect of an AlO layer on the electrical properties was investigated in HfO-AlO 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 AlO passivation layer and its sequence in the HfO-AlO laminate structures. Because of the interfacial reaction, the AlO/HfO/AlO structure showed the best electrical characteristics. The top AlO layer suppressed the interdiffusion of oxidizing species into the HfO films, whereas the bottom AlO layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was more effectively suppressed in the AlO/HfO/AlO/InP structure than that in the HfO-on-InP system. Moreover, conductance data revealed that the AlO layer on InP reduces the midgap traps to 2.6 × 10 eV cm (compared to that of HfO/InP, that is, 5.4 × 10 eV cm). 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.