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

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The passivation effect of an Al 2 O 3 layer on the electrical properties was investigated in HfO 2 –Al 2 O 3 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 Al 2 O 3 passivation layer and its sequence in the HfO 2 –Al 2 O 3 laminate structures. Because of the interfacial reaction, the Al 2 O 3 /HfO 2 /Al 2 O 3 structure showed the best electrical characteristics. The top Al 2 O 3 layer suppressed the interdiffusion of oxidizing species into the HfO 2 films, whereas the bottom Al 2 O 3 layer blocked the outdiffusion of In and P atoms. As a result, the formation of In–O bonds was more effectively suppressed in the Al 2 O 3 /HfO 2 /Al 2 O 3 /InP structure than that in the HfO 2 -on-InP system. Moreover, conductance data revealed that the Al 2 O 3 layer on InP reduces the midgap traps to 2.6 × 10 12 eV –1 cm –2 (compared to that of HfO 2 /InP, that is, 5.4 × 10 12 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.