Abstract
We report on the advantages of using Graphene-Insulator-Semiconductor (GIS) instead of Metal-Insulator-Semiconductor (MIS) structures in reliable and precise photoelectric determination of the band alignment at the semiconductor-insulator interface and of the insulator band gap determination. Due to the high transparency to light of the graphene gate in GIS structures large photocurrents due to emission of both electrons and holes from the substrate and negligible photocurrents due to emission of carriers from the gate can be obtained, which allows reliable determination of barrier heights for both electrons, Ee and holes, Eh from the semiconductor substrate. Knowing the values of both Ee and Eh allows direct determination of the insulator band gap EG(I). Photoelectric measurements were made of a series of Graphene-SiO2-Si structures and an example is shown of the results obtained in sequential measurements of the same structure giving the following barrier height values: Ee = 4.34 ± 0.01 eV and Eh = 4.70 ± 0.03 eV. Based on this result and results obtained for other structures in the series we conservatively estimate the maximum uncertainty of both barrier heights estimations at ± 0.05 eV. This sets the SiO2 band gap estimation at EG(I) = 7.92 ± 0.1 eV. It is shown that widely different SiO2 band gap values were found by research groups using various determination methods. We hypothesize that these differences are due to different sensitivities of measurement methods used to the existence of the SiO2 valence band tail.
Highlights
Band diagram is a fundamental property of any semiconductor device
A comparison of RTA characteristics calculated using these methods for Al-SiO2-Si (MIS) capacitor and for Graphene-SiO2-Si (GIS) capacitor – both with the SiO2 layer thickness of 86 nm, as in the samples described in the experimental part of this work – is shown in Fig. 2, demonstrating that in the GIS structure the fraction of the light beam power absorbed by the graphene gate (A) is negligible in comparison with the power absorbed by the substrate (T)
Photoelectric measurements of the GIS structures were made in the configuration shown in Fig. 6, using the semiautomatic multifunctional system for photoelectric measurements (MSPM) of our own design, which is composed of several high-class subsystems guaranteeing high accuracy of the measurement results
Summary
Band diagram is a fundamental property of any semiconductor device. Knowledge of the band diagram of a device allows predicting its most important electronic properties. A comparison of RTA characteristics calculated using these methods for Al-SiO2-Si (MIS) capacitor and for Graphene-SiO2-Si (GIS) capacitor – both with the SiO2 layer thickness of 86 nm, as in the samples described in the experimental part of this work – is shown, demonstrating that in the GIS structure (as opposed to the MIS structure) the fraction of the light beam power absorbed by the graphene gate (A) is negligible in comparison with the power absorbed by the substrate (T). This allows for unimpeded photocurrent measurement, due to hole emission from the. The samples investigated in this study have the insulator layer thickness of d2=86 nm which fulfills this requirement making the fraction of light power absorbed by the graphene gate negligible in comparison with light power absorbed by the substrate, as shown in Fig. 2 and illustrated in Fig. 4 for a range of wavelengths and insulator thicknesses
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