Van der Pauw method

About: Van der Pauw method is a research topic. Over the lifetime, 1682 publications have been published within this topic receiving 25364 citations.

Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping.

Abstract: We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.

Thermal neutron irradiation experiments on 10BP single-crystal wafers☆

Abstract: The electrical properties of 10 BP wafers grown by chemical vapour deposition at room temperature before and after irradiation by thermal neutrons were measured by the van der Pauw method. No appreciable change in electrical properties was observed for the (100) wafer. In the case of the (111) wafer, the carrier concentration for the n type increased and decreased for the p type after irradiation with thermal neutrons owing to the formation of donors caused by nuclear reaction of 10 B(n,α) 7 Li. The electrical conductivity σ, the carrier concentration n and the mobility μ of the (111) wafer after irradiation were measured at high temperatures: n decreased and μ increased for the p type (and vice versa for the n type) compared with the values before irradiation. The temperature dependence of carrier concentration before and after irradiation was correlated with the theoretical curves to calculate the donor and acceptor concentrations and their activation energies.

Characterization of 4H-SiC Epitaxial Layers and High-Resistivity Bulk Crystals for Radiation Detectors

Abstract: Defect and electrical characterization of bulk semi-insulating (SI) 4H-SiC crystals and SI and n-type 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD) on highly doped (0001) 4H-SiC substrates is reported. Optical microscopy, electron beam induced current (EBIC) imaging, current-voltage ( $I$ – $V$ ) measurements, thermally stimulated current (TSC) spectroscopy (94 K–620 K), Hall effect, and van der Pauw measurements have been conducted for characterization and defect correlation studies. Both epitaxial layers exhibited relatively shallow levels related to Al, B, $L$ - and D-centers. Deep level centers in the n-type epitaxial layer peaked at ${\sim} 400$ K ( $E_{a} \sim 1.1$ eV), and ${\sim} 470$ K were correlated with $IL_{2}$ defect and 1.1 eV center in high-purity bulk SI 4H-SiC. The SI epitaxial layer exhibited peak at ${\sim} 290$ K ( $E_{a} = 0.82\hbox{--}0.87$ eV) that was attributed to $IL_{1}$ and HK2 centers, and at ${\sim} 525$ K that was related to intrinsic defects and their complexes with energy levels close to the middle of the band-gap. Results of EBIC and optical microscopy showed segregation of threading dislocations around comet tail defects in the n-type epitaxial layer. The $I$ – $V$ characteristics of the devices on SI epitaxial layer exhibited steps corresponding to the ultimate trap filling of deep centers. The high-temperature resistivity measurements of bulk SI 4H-SiC sample revealed resistivity hysteresis that was attributed to the filling of the deep-level electron trap centers. The responsivity of the n-type epitaxial 4H-SiC detector in the soft X-ray energy range is reported for the first time.

Simple analytical method for determining electrical resistivity and sheet resistance using the van der Pauw procedure.

Abstract: This work reports an analytical method for determining electrical resistivity (ρ) and sheet resistance (RS) of isotropic conductors. The method is compared with previous numerical solutions and available experimental data showing a universal behavior for isotropic conductors. An approximated solution is also reported allowing one to easily determine ρ and RS for samples either with regular or arbitrary shapes.