Analysis of inhomogeneous Ge/SiC heterojunction diodes

Abstract

In this article Schottky barrier diodes comprising of a n-n Germanium-Silicon Carbide (Ge-SiC) heterojunction are electrically characterised. Circular transmission line measurements prove that the nickel front and back contacts are ohmic, isolating the Ge/SiC heterojunction as the only contributor to the Schottky behaviour. Current-voltage plots taken at varying temperature (IVT) reveal that the ideality factor (n) and Schottky barrier height (Φ) are temperature dependent and that incorrect values of the Richardson constant (A * * ) are being produced, suggesting an inhomogeneous barrier. Techniques originally designed for metal-semiconductor SBH extraction are applied to the heterojunction results to extract values of Φ and A * * that are independent of temperature. The experimental IVT data is replicated using the Tung model. It is proposed that small areas, or patches, making up only 3% of the total contact area will dominate the I-V results due to their low SBH of 1.033 eV. The experimental IVT data is also analysed statistically using the extracted values of Φ to build up a Gaussian distribution of barrier heights, including the standard deviation and a mean SBH of 1.126 eV, which should be analogous to the SBH extracted from capacitance-voltage (C-V) measurements. Both techniques yield accurate values of A * * for SiC. However, the C-V analysis did not correlate with the mean SBH as expected.

The rectenna device: From theory to practice (a review)

“…Instead, a more realistic scenario should be considered where multiple current paths exist flowing over barriers of different barrier height, so modifying this equation that has been the standard for a century or more. The papers by Tung 151,160 and others [155][156][157][158][159] pro-vide a much more rigorous understanding of the Schottky diode and its operation under this inhomogeneous regime. Given the small potential size of a Schottky rectenna, the impact of such interface inhomogeneity will be the source of significant device-device variation, and an unpredictability of cut-off frequencies.…”

Interface characteristics of n-n and p-n Ge/SiC heterojunction diodes formed by molecular beam epitaxy deposition

“…More recently, we have reported on Ge/SiC heterojunctions 12,13 due to the materials even higher mobility (especially in p-type where the hole mobility is 5 times that of Si and 21 times that of SiC) and the development of very good Ge/High-K dielectric interfaces 14 . With the Ge having been deposited via MBE and given ohmic front and back contacts, Schottky-like behaviour was demonstrated with the structures displaying a turn-on voltage of only 0.3 V and an ideality factor less than 1.1.…”

A study of temperature-related non-linearity at the metal-silicon interface

“…Tung states 9 that at low temperature, Ohmic effects within the few conducting patches cause the dual current paths to become deconvoluted. This might explain the frequently cited and debated double bumps that can be seen variously in Si Schottky diodes 9,11 , SiC diodes [16][17][18][19][20] , GaAs diodes 23,24 , and also in heterojunctions 12,25 . The worsening of these effects in devices without guard rings or other edge protection, could futher be explained by low SBH patches at the device extremities which are not pinched off as well as those in the centre of the device, these being surrounded on all sides by the higher background patches [9][10][11] .…”

“…Other applications include carbon nanotube Schottky barrier transistors 6 , and Schottky solar cells, with materials including lead selenide nanocrystals 7 and graphene 8 . Despite over a hundred years of research and development into Schottky barriers, across all popular semiconductors and for the various applications, we still find ourselves with unanswered questions as to the nature of current flow across the barrier, especially in light of inhomogeneity at the metal-semiconductor interface 9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24] , which can result in multiple conduction paths through the non-uniform interface. Sources of interfacial inhomogeneity include processing remnants (dirt, contamination), surface roughness, native oxide, an uneven doping profile, crystal defects and grain boundaries 9,11,12 and it is generally now accepted that the surface is better represented as a random array of different patches, each of varying barrier height and area, as represented in the inset of Figure 1a.…”

“…Interfacial inhomogeneity has been cited 9-24 as the cause for many experimental results that deviate from this response. These so called non-linearities include high ideality factors 9,11,13 , the discrepancy between Schottky barrier heights (SBH) extracted via CV and IV techniques [9][10][11][12][13][14][15] , the "T 0 anomaly" 9,11,13 , double bumps within the semi-log turn-on characteristics 9,11,13,[16][17][18][19][20] , edge effects 9,11 and non-linearity within Richardson plots 22 . It was the papers written by Tung [9][10][11] however, that first introduced a model that adapted Equation 1 to fully explain the non-linearities in light of interfacial inhomogeneity and SBH fluctuation.…”