Barrier height distribution and dipolar relaxation in metal-insulator-semiconductor junctions with molecular insulator: Ageing effects

Abstract

To cite this version:Alain-Bruno Fadjie-Djomkam, Soraya Ababou-Girard, Christian Godet. Barrier height distribution and dipolar relaxation in metal-insulator-semiconductor junctions with molecular insulator: Ageing effects. Journal of Applied Physics, American Institute of Physics, 2012, 112, pp.113701-1-113701-11 Related ArticlesAtomic layer deposition of Al2O3 on GaSb using in situ hydrogen plasma exposure Appl. Phys. Lett. 101, 231601 (2012) Defect induced mobility enhancement: Gadolinium oxide (100) on Si(100) Appl. Phys. Lett. 101, 222903 (2012) Band alignment in Ge/GeOx/HfO2/TiO2 heterojunctions as measured by hard x-ray photoelectron spectroscopy Appl. Phys. Lett. 101, 222110 (2012) Electronic properties at the oxide interface with silicon and germanium through x-ray induced oxide charging Appl. Phys. Lett. 101, 211606 (2012) A computational study of graphene silicon contact J. Appl. Phys. 112, 104502 (2012) Additional information on J. Appl. Phys. Electrical transport through molecular monolayers being very sensitive to disorder effects, admittance and current density characteristics of Hg//C 12 H 25 -n Si junctions incorporating covalently bonded n-alkyl molecular layers, were investigated at low temperature (150-300 K), in the as-grafted state and after ageing at the ambient. This comparison reveals local oxidation effects both at the submicron scale in the effective barrier height distribution and at the molecular scale in the dipolar relaxation. In the bias range dominated by thermionic emission and modified by the tunnel barrier (TB) attenuation, expðÀb 0 d T Þ, where d T is the thickness of the molecular tunnel barrier and b 0 is the inverse attenuation length at zero applied bias, some excess current is attributed to a distribution of low barrier height patches.Complementary methods are used to analyze the current density J(V, T) characteristics of metal-insulator-semiconductor tunnel diodes. Assuming a Gaussian distribution of barrier heights centered at qU B provides an analytical expression of the effective barrier height, qU EFF ðTÞ ¼ qU B þ ðkTÞb 0 d T À ðqdUÞ 2 =2kT; this allows fitting of the distribution standard deviation dU and tunnel parameter ðb 0 d T Þ over a wide temperature range. In a more realistic modeling including the voltage dependence of barrier height and circular patch area, the so-called "pinch-off" effect is described by a distribution of parameter c ¼ 3ðD P R 2 P =4Þ 1=3 , which combines interface potential modulation and patch area variations. An arbitrary distribution of c values, fitted to low-temperature J(V) data, is equally well described by Gaussian or exponential functions. Ageing in air also increases the interface oxidation of Si substrate and affects the density of localized states near mid gap, which typically rises to the high 10 11 eV À1 cm À2 range, as compared with D S < 10 11 eV À1 cm À2 in the as-grafted state. The bias-independent relaxation observed near 1 kHz at low temperature may be attributed either to dipoles in the alkyl chain in...

Effect of high current density on the admittance response of interface states in ultrathin MIS tunnel junctions

“…42 The power law dependence of the measured conductance, , is very different from the high frequency plateau expected for a MIS tunnel device with homogeneous barrier height.…”

“…This conclusion is consistent with low temperature dc current characteristics of molecular tunnel junctions. 42 Note that the excess capacitance will be less affected than the excess conductance since the space charge layer thickness is weakly dependent on the interface potential fluctuations. Hence, we expect that the homogeneous model still applies to experimental excess capacitance results.…”

“…As an illustration, in a study of long term stability of molecular devices (ageing at the ambient for eighteen months), a significant increase has been observed in the dipolar relaxation capacitance (x 50) and in the interface states response (x 7) of the Hg // C 12 H 25 -Si junction; besides the appearance of an interface silicon oxide layer revealed by XPS, some presence of adsorbed water vapour cannot be excluded. 42 This effect could be possibly delayed or suppressed by engineering a very compact molecular layer. 47 To understand the admittance response of interface states, we have proposed a representation of the excess capacitance, ( -), as a function of the dc current density, , which clearly reveals the different regimes predicted by modelling the non equilibrium tunnel MIS junction in the forward bias range.…”

“…[39][40][41] A similar effect has been observed in molecular tunnel junctions, after ageing at the ambient. 42 In this case, for a given applied bias value, low barrier height patches with a high local dc current density may result in a distribution of values (tailing towards shorter times, Eqn 7). As a consequence, the interface states conductance is a sum (weighted by the effective patch area ) of local conductance values defined by their characteristic angular frequency and high frequency plateau value (Eqn 16).…”

Low temperature nanoscale electronic transport on the MoS2 surface

“…Ideality factors greater than ı = 1.5 at room temperature and increasing at low temperatures have been measured for MIS junctions using molecular insulators 32,33 . In this case, the departure from ı = 1 is attributed to recombination effects at the interface 34,35 . Detailed understanding of non-ideality requires further investigation of such nanoscale MIS junctions which is beyond the scope of this Letter.…”