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Localized Tail States and Electron Mobility in Amorphous ZnON Thin Film Transistors.

Lee S, Nathan A, Ye Y, Guo Y, Robertson J - Sci Rep (2015)

Bottom Line: The extracted values of tail state density at the conduction band minima (N(tc)) and its characteristic energy (kT(t)) are about 2 × 10(20) cm(-3)eV(-1) and 29 meV, respectively, suggesting trap-limited conduction prevails at room temperature.Based on trap-limited conduction theory where these tail state parameters are considered, electron mobility is accurately retrieved using a self-consistent extraction method along with the scaling factor '1/(α + 1)' associated with trapping events at the localized tail states.Additionally, it is found that defects, e.g. oxygen and/or nitrogen vacancies, can be ionized under illumination with hv ≫ E(g), leading to very mild persistent photoconductivity (PPC) in a-ZnON TFTs.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, United Kingdom.

ABSTRACT
The density of localized tail states in amorphous ZnON (a-ZnON) thin film transistors (TFTs) is deduced from the measured current-voltage characteristics. The extracted values of tail state density at the conduction band minima (N(tc)) and its characteristic energy (kT(t)) are about 2 × 10(20) cm(-3)eV(-1) and 29 meV, respectively, suggesting trap-limited conduction prevails at room temperature. Based on trap-limited conduction theory where these tail state parameters are considered, electron mobility is accurately retrieved using a self-consistent extraction method along with the scaling factor '1/(α + 1)' associated with trapping events at the localized tail states. Additionally, it is found that defects, e.g. oxygen and/or nitrogen vacancies, can be ionized under illumination with hv ≫ E(g), leading to very mild persistent photoconductivity (PPC) in a-ZnON TFTs.

No MeSH data available.


(a) Extracted carrier densities (nfree and ntrap) and (b) density of tail states denoted as Ntail(E).The extracted Ntail(E) for different VDS is similar to each other, suggesting that the extraction method is almost independent on VDS when VDS is small enough. This also implies that contact resistance effects are negligible at small VDS, e.g. 0.1 V and 0.01 V.
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f3: (a) Extracted carrier densities (nfree and ntrap) and (b) density of tail states denoted as Ntail(E).The extracted Ntail(E) for different VDS is similar to each other, suggesting that the extraction method is almost independent on VDS when VDS is small enough. This also implies that contact resistance effects are negligible at small VDS, e.g. 0.1 V and 0.01 V.

Mentions: Based on the above extraction method, the density of localized tail states was retrieved using a-ZnON TFTs with W = 50 μm and L = 10 μm. Here, the linear IDS − VGS characteristics were measured at a small VDS (e.g. 0.01 V and 0.1 V), as seen in Fig. 2(a,b) shows output characteristics for different VGS (see also Figure S2 in the Supplementary Information). The basic parameter to be extracted from each I-V curve is VT. The VT values of these two cases (VDS = 0.01 V and 0.1 V) are 4.4 V and 4.3 V, respectively. The other unknown parameters, μband and Cox are 110 cm2/V-s and 19 nF/cm2, respectively8. Here, μband can be the maximum achievable mobility and the Cox value was calculated using a thickness of 300 nm and measured permittivity of ~6.5ε0 for the gate insulator Si3N4. Using these parameters and Equations (1, 2, 3, 4, 5, 6), the carrier densities (nfree and ntrap) and density of tail states (Ntail(E)) were extracted as seen in Fig. 3a,b, respectively. As indicated in Fig. 3b, the tail states (i.e. gap states near the EC) can be approximated as an exponential distribution141516,Here, Ntc is the tail state density at E = EC (i.e. conduction band minima), and kTt is the characteristic energy of the tail state. Applying Equation (7) into the plot shown in Fig. 3b, Ntc and kTt values were extracted as 2 × 1020 cm−3eV−1 and 29 meV, respectively.


Localized Tail States and Electron Mobility in Amorphous ZnON Thin Film Transistors.

Lee S, Nathan A, Ye Y, Guo Y, Robertson J - Sci Rep (2015)

(a) Extracted carrier densities (nfree and ntrap) and (b) density of tail states denoted as Ntail(E).The extracted Ntail(E) for different VDS is similar to each other, suggesting that the extraction method is almost independent on VDS when VDS is small enough. This also implies that contact resistance effects are negligible at small VDS, e.g. 0.1 V and 0.01 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4548246&req=5

f3: (a) Extracted carrier densities (nfree and ntrap) and (b) density of tail states denoted as Ntail(E).The extracted Ntail(E) for different VDS is similar to each other, suggesting that the extraction method is almost independent on VDS when VDS is small enough. This also implies that contact resistance effects are negligible at small VDS, e.g. 0.1 V and 0.01 V.
Mentions: Based on the above extraction method, the density of localized tail states was retrieved using a-ZnON TFTs with W = 50 μm and L = 10 μm. Here, the linear IDS − VGS characteristics were measured at a small VDS (e.g. 0.01 V and 0.1 V), as seen in Fig. 2(a,b) shows output characteristics for different VGS (see also Figure S2 in the Supplementary Information). The basic parameter to be extracted from each I-V curve is VT. The VT values of these two cases (VDS = 0.01 V and 0.1 V) are 4.4 V and 4.3 V, respectively. The other unknown parameters, μband and Cox are 110 cm2/V-s and 19 nF/cm2, respectively8. Here, μband can be the maximum achievable mobility and the Cox value was calculated using a thickness of 300 nm and measured permittivity of ~6.5ε0 for the gate insulator Si3N4. Using these parameters and Equations (1, 2, 3, 4, 5, 6), the carrier densities (nfree and ntrap) and density of tail states (Ntail(E)) were extracted as seen in Fig. 3a,b, respectively. As indicated in Fig. 3b, the tail states (i.e. gap states near the EC) can be approximated as an exponential distribution141516,Here, Ntc is the tail state density at E = EC (i.e. conduction band minima), and kTt is the characteristic energy of the tail state. Applying Equation (7) into the plot shown in Fig. 3b, Ntc and kTt values were extracted as 2 × 1020 cm−3eV−1 and 29 meV, respectively.

Bottom Line: The extracted values of tail state density at the conduction band minima (N(tc)) and its characteristic energy (kT(t)) are about 2 × 10(20) cm(-3)eV(-1) and 29 meV, respectively, suggesting trap-limited conduction prevails at room temperature.Based on trap-limited conduction theory where these tail state parameters are considered, electron mobility is accurately retrieved using a self-consistent extraction method along with the scaling factor '1/(α + 1)' associated with trapping events at the localized tail states.Additionally, it is found that defects, e.g. oxygen and/or nitrogen vacancies, can be ionized under illumination with hv ≫ E(g), leading to very mild persistent photoconductivity (PPC) in a-ZnON TFTs.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, United Kingdom.

ABSTRACT
The density of localized tail states in amorphous ZnON (a-ZnON) thin film transistors (TFTs) is deduced from the measured current-voltage characteristics. The extracted values of tail state density at the conduction band minima (N(tc)) and its characteristic energy (kT(t)) are about 2 × 10(20) cm(-3)eV(-1) and 29 meV, respectively, suggesting trap-limited conduction prevails at room temperature. Based on trap-limited conduction theory where these tail state parameters are considered, electron mobility is accurately retrieved using a self-consistent extraction method along with the scaling factor '1/(α + 1)' associated with trapping events at the localized tail states. Additionally, it is found that defects, e.g. oxygen and/or nitrogen vacancies, can be ionized under illumination with hv ≫ E(g), leading to very mild persistent photoconductivity (PPC) in a-ZnON TFTs.

No MeSH data available.