Abstract
In this study, the current conduction mechanisms of structures with tandem high-k dielectric in illumination are discussed. Samples of Al/SiO2/Si (S), Al/HfO2/SiO2/Si (H), and Al/3HfO2/SiO2/Si (3H) were examined. The significant observation of electron traps of sample H compares to sample S is found under the double bias capacitance-voltage (C-V) measurements in illumination. Moreover, the photo absorption sensitivity of sample H is higher than S due to the formation of HfO2 dielectric layer, which leads to larger numbers of carriers crowded through the sweep of VG before the domination of tunneling current. Additionally, the HfO2 dielectric layer would block the electrons passing through oxide from valance band, which would result in less electron-hole (e−-h+) pairs recombination effect. Also, it was found that both of the samples S and H show perimeter dependency of positive bias currents due to strong fringing field effect in dark and illumination; while sample 3H shows area dependency of positive bias currents in strong illumination. The non-uniform tunneling current through thin dielectric and through HfO2 stacking layers are importance to MOS(p) tunneling photo diodes.
Highlights
When reducing the SiO2 thickness in complementary metal-oxide-semiconductor (CMOS) devices to enhance the packaging density, the gate oxide encounters the problem of excessive gate leakage current, which would result in increased static power consumption and error read in logic device.[1]
We found that the illumination sensitivity of sample H is better than sample S
The onset voltage of sample H entering deep depletion and the current saturation would become larger under illumination condition
Summary
When reducing the SiO2 thickness in complementary metal-oxide-semiconductor (CMOS) devices to enhance the packaging density, the gate oxide encounters the problem of excessive gate leakage current, which would result in increased static power consumption and error read in logic device.[1]. Since the application of MOS structures with high-k as photo sensor is becoming important, a detailed study of the current conduction through devices is worthwhile to explore. The capacitance-voltage (C-V) and current-voltage (I-V) measurements in dark and illumination of structures Al/SiO2/Si (sample S, with thickness 1.8nm), Al/HfO2/SiO2/Si (sample H, with interfacial layer 1.4nm and HfO2 physical thickness 3.1nm) and Al/3HfO2/SiO2/Si (sample 3H) are discussed. It is noticed that the inversion current of MOS photodiode with specific perimeter dependency was reported.[23,24] in this work, it was found that the I-V characteristic of sample 3H shows area but not perimeter dependency when measured under illumination with high intensity.
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