Monte Carlo Study of 2-D Capacitance Fringing Effects in GaAs Planar Schottky Diodes

Abstract

International audienceNanometer scale planar Schottky barrier diodes with realistic geometries have been studied by means of a two-dimensional ensemble Monte Carlo simulator. The topology of the devices studied in this work is based in real planar GaAs Schottky barrier diodes used in THz applications, such as passive frequency mixing and multiplication, in which accurate models for the diode capacitance are required. The intrinsic capacitance of such small devices, which due to edge effects strongly deviates from the ideal value, has been calculated. In good agreement with the classical models, we have found that the edge capacitance is independent of the properties of the semiconductor beneath the contact and, as novel result, that the presence of surface charges at the semiconductor dielectric interface can reduce it almost 15%. We have finally provided a compact model for the total capacitance of diodes with arbitrary shape that could be easily implemented in design automation software such as ADS

Dielectric Passivation and Edge Effects in Planar GaN Schottky Barrier Diodes

“…1. In such a case, the absolute diode capacitance is given by [10], where the absolute ideal capacitance C T ideal is proportional to the area of the anode A and the absolute EE contribution C T EE to the length of its contour L contour . We neglect a second-order correction, independent of the geometry, associated with EEs accounting for the nonrectangular shape of the anode [3], [10].…”

“…In such a case, the absolute diode capacitance is given by [10], where the absolute ideal capacitance C T ideal is proportional to the area of the anode A and the absolute EE contribution C T EE to the length of its contour L contour . We neglect a second-order correction, independent of the geometry, associated with EEs accounting for the nonrectangular shape of the anode [3], [10]. In the case of a circular anode, A = πr 2 and L contour = 2πr , with r being the radius of the anode, equivalent to L Sch in our 2-D calculations considering that the simulation domain represented in Fig.…”

“…For the calculations, a semiclassical ensemble MC simulator of carrier transport self-consistently coupled with a 2-D Poisson solver has been used [10]- [12]. The conduction band of GaN is formed of three nonparabolic spherical valleys: 1 , U , and 3 [10], [13], [14]. Ionized impurities, alloy, polar This work is licensed under a Creative Commons Attribution 4.0 License.…”

“…The layer structure consists of a highly doped substrate with doping N S = 5 • 10 18 cm −3 and an epilayer with doping N E = 3 • 10 17 cm −3 . The Schottky contact is placed on the top of the epilayer and is modeled as a perfect absorbing boundary [10], [12], [16]. The stepped ohmic contact imposes charge neutrality in the proximity of the electrode by injecting thermal carriers [17].…”

“…The SCCM has been validated in previous works [19]- [22]. The total capacitance (per unit length) C(V ) = C Ideal + C EE is given by the sum of the ideal capacitance C Ideal = L sch • sc /W (V ) and the EE capacitance C EE = β • sc [10], [20], where sc is the permittivity of the semiconductor, W (V ) the depth of the depletion region, and L sch the length of the Schottky contact. The dimensionless parameter β, characteristic of EEs, is determined and analyzed as in [20].…”