Vito Raineri

Richardson's constant in inhomogeneous silicon carbide Schottky contacts

The electrical characterization of nickel silicide Schottky contacts on silicon carbide (4H–SiC) is reported in this article. In spite of the nearly ideal behavior of the contact at room temperature (n=1.05), the electrical behavior monitored in a wide temperature range exhibited a deviation from the ideality at lower temperatures, thus suggesting that an inhomogeneous barrier has actually formed. A description of the experimental results by the Tung’s model, i.e., considering an effective area of the inhomogeneous contact, provided a procedure for a correct determination of the Richardson’s constant A**. An effective area lower than the geometric area of the diode is responsible for the commonly observed discrepancy in the experimental values of A** from its theoretical value in silicon carbide. The same method was applied to Ti/4H–SiC contacts.

Barrier inhomogeneity and electrical properties of Pt∕GaN Schottky contacts

The temperature dependence of the electrical properties of Pt∕GaN Schottky barrier was studied. In particular, a Schottky barrier height of 0.96eV and an ideality factor of 1.16 were found after a postdeposition annealing at 400°C. Nanoscale electrical characterization was carried out by the conductive biased tip of an atomic force microscope both on the bare GaN surface and on the Pt∕GaN contacts. The presence of a lateral inhomogeneity of the Schottky barrier, with a Gaussian distribution of the barrier height values, was demonstrated. Moreover, GaN surface defects were demonstrated to act as local preferential paths for the current conduction. The temperature dependent electrical characteristics of the diodes were discussed in terms of the existing models on inhomogeneous barriers and correlated to the nanoscale electrical characterization of the barrier. In this way, the anomalous electrical behavior of the ideality factor and of the Schottky barrier and the low experimental value of the Richardson’s ...

High responsivity 4H-SiC Schottky UV photodiodes based on the pinch-off surface effect

In this letter, high responsivity 4H-SiC vertical Schottky UV photodiodes based on the pinch-off surface effect, obtained by means of self-aligned Ni2Si interdigit contacts, are demonstrated. The diode area was 1mm2, with a 37% directly exposed to the radiation. The dark current was about 200pA at −50V. Under a 256nm UV illumination, a current increase of more than two orders of magnitude is observed, resulting in a 78% internal quantum efficiency. The vertical photodiodes showed an ultraviolet-visible rejection ratio >7×103 and a responsivity a factor of about 1.8 higher than a conventional planar metal-semiconductor-metal structure.

Reduction of boron diffusion in silicon by 1 MeV 29Si+ irradiation

Reduction of the transient diffusion of B, implanted in Si along [100] at 10 keV to a dose of 1×1013/cm2, after annealing at 900 °C for 10 s has been observed in samples irradiated with 1.0 MeV 29Si ions to a dose of 5×1013/cm2 or higher. A lower Si dose did not influence the transient B tail diffusion. Secondary defects formed near the peak of the 1 MeV Si damage distribution, for doses of 5×1013/cm2 and higher, act as efficient sinks for interstitials from shallower depths and thereby reduce the transient tail diffusion.

Mapping the Density of Scattering Centers Limiting the Electron Mean Free Path in Graphene

Recently, giant carrier mobility μ (>10(5) cm(2) V(-1) s(-1)) and micrometer electron mean free path (l) have been measured in suspended graphene or in graphene encapsulated between inert and ultraflat BN layers. Much lower μ values (10000-20000 cm(2) V(-1) s(-1)) are typically reported in graphene on common substrates (SiO(2), SiC) used for device fabrication. The debate on the factors limiting graphene electron mean free path is still open with charged impurities (CI) and resonant scatterers (RS) indicated as the most probable candidates. As a matter of fact, the inhomogeneous distribution of such scattering sources in graphene is responsible of nanoscale lateral inhomogeneities in the electronic properties, which could affect the behavior of graphene nanodevices. Hence, high resolution two-dimensional (2D) mapping of their density is very important. Here, we used scanning capacitance microscopy/spectroscopy to obtain 2D maps of l in graphene on substrates with different dielectric permittivities, that is, SiO(2) (κ(SiO2) = 3.9), 4H-SiC (0001) (κ(SiC) = 9.7) and the very-high-κ perovskite strontium titanate, SrTiO(3) (001), briefly STO (κ(STO) = 330). After measuring l versus the gate bias V(g) on an array of points on graphene, maps of the CI density (N(CI)) have been determined by the neutrality point shift from V(g) = 0 V in each curve, whereas maps of the RS density (N(RS)) have been extracted by fitting the dependence of l on the carrier density (n). Laterally inhomogeneous densities of CI and RS have been found. The RS distribution exhibits an average value ∼3 × 10(10) cm(-2) independently on the substrate. For the first time, a clear correlation between the minima in the l map and the maxima in the N(CI) map is obtained for graphene on SiO(2) and 4H-SiC, indicating that CI are the main source of the lateral inhomogeneity of l. On the contrary, the l and N(CI) maps are uncorrelated in graphene on STO, while a clear correlation is found between l and N(RS) maps. This demonstrates a very efficient dielectric screening of CI in graphene on STO and the role of RS as limiting factor for electron mean free path.

Temperature behavior of inhomogeneous Pt∕GaN Schottky contacts

In this letter, a correlation between the nanoscale localized electrical properties of the Pt∕GaN Schottky barrier and the temperature behavior of macroscopic Schottky diodes is demonstrated. Although a significant improvement of the ideality factor of the diodes is achieved after annealing at 400°C, local current-voltage measurements, performed with a biased tip of a conductive atomic force microscope, revealed the inhomogeneous nature of the barrier. Its nanoscale degree of homogeneity was quantitatively described by means of Tung’s model [Phys. Rev. B 45, 13509 (1992)], allowing the authors to explain the temperature dependence of the electrical characteristics of the macroscopic diodes.

Dielectric properties of Pr2O3 high-k films grown by metalorganic chemical vapor deposition on silicon

Praseodymium oxide (Pr2O3) thin films have been deposited on Si(100) substrates by metalorganic chemical vapor deposition using praseodymium tris-2,2,6,6-tetramethyl-3,5-heptandionate as source material. Film structural, morphological, and compositional characterizations have been carried out. Dielectric properties have been studied as well by capacitance–voltage and current–voltage measurements on metal-oxide-semiconductor capacitors of several areas. The Pr2O3 films have shown a dielectric constant e=23–25 and a leakage current density of 8.8×10−8 A/cm2 at +1 V.

Highly Efficient Low Reverse Biased 4H-SiC Schottky Photodiodes for UV-Light Detection

Ultraviolet light detection has a wide range of scientific and industrial applications. In particular, SiC photodiodes have been proposed because of their robustness even in harsh environments, high quantum efficiency but excellent visible blindness, very low dark current, and high speed. Here, we report on the electrical and optical performances of high efficient large area 4 H-SiC Schottky photodiodes working in the photovoltaic regime. We demonstrate that the high signal-to-noise ratio along with the low operating reverse voltage in spite of the large sensitive area makes them suitable in low power consumption applications requiring high sensitivity down to 250 nm.

OHMIC CONTACTS TO SIC

In this chapter, the most significant results obtained in the last decade in the field of ohmic contacts to SiC are reviewed. First, the basic concepts related to the physics of ohmic contacts and to the contact resistance measurement techniques are briefly reported. Then, some aspects concerning the formation of low resistance (10-5-10-6 Ωcm2) ohmic contacts on n-type and for p-type SiC are discussed, focusing on Ni-based and Al/Ti-based contacts. Examples of innovative applications on practical devices are also reported, as the simultaneous formation of ohmic contacts on n- and p-type SiC for vertical power MOS devices, obtained adding Al to a standard Ni contact, and a single-metal technology for ohmic and rectifying contacts in MESFETs, using Ti or Ni without post-deposition annealing.

Study of interface states and oxide quality to avoid contrast reversal in scanning capacitance microscopy

We demonstrate that the contrast reversal effect in scanning capacitance microscopy (SCM) is related to the Si/SiO2 interface microroughness. The surface roughness has been associated with the concentration of states at the Si/SiO2 interface and a monotonic behavior of the SCM imaging is preferentially observed for a smooth surface and consequently a low state concentration. Changes in the oxide quality have also been found to strongly influence the measurements. A criterion based on the hysteresis measurements from forward and reverse dC/dV–V curves is discussed to better evaluate the oxide quality and to obtain reproducible SCM data.