Graphene-GaN Schottky diodes

Abstract

The electrical characteristics of graphene Schottky contacts formed on undoped GaN semiconductors were investigated. Excellent rectifying behavior with a rectification ratio of ~10 7 at ±2 V and a low reverse leakage current of 1.0 × 10 -8 A/cm 2 at -5 V were observed. The Schottky barrier heights, as determined by the thermionic emission model, Richardson plots, and barrier inhomogeneity model, were 0.90, 0.72, and 1.24 ± 0.13 eV, respectively. Despite the predicted low barrier height of ~0.4 eV at the graphene-GaN interface, the formation of excellent rectifying characteristics with much larger barrier heights is attributed to the presence of a large number of surface states (1.2 × 10 13 states/cm 2 /eV) and the internal spontaneous polarization field of GaN, resulted in a significant upward surface band bending or a bare surface barrier height as high as of 2.9 eV. Using the S parameter of 0.48 (measured from the work function dependence of Schottky barrier height) and the mean barrier height of 1.24 eV, the work function of graphene in the Au/graphene/GaN stack could be approximately estimated to be as low as 3.5 eV. The obtained results indicate that graphene is a promising candidate for use as a Schottky rectifier in GaN semiconductors with n-type conductivity.

Current transport mechanism in graphene/AlGaN/GaN heterostructures with various Al mole fractions

“…19 The result of Ref. 19 matches well with our experimental SBH results for graphene on AlGaN layers. Two features can be extracted from Fig.…”

“…Song et al studied the work function of graphene with different metal contacts (Au, Pd, Ni and Cr/Au) and postulated the work function of graphene to be 4.62 eV for an Au contact on graphene, 27 which is larger than the known value. 19 Note that the work function tuning of graphene may be of marginal effect. (3) Above all, the SBH for graphene/AlGaN layers is affected by another mechanism such as Schottky barrier inhomogeneity and the surface Fermi level pinning caused by the large surface states and polarization field of the AlGaN.…”

“…[15][16][17][18] Kim et al showed a Schottky barrier height (SBH) of 0.9 eV for the graphene contact on a GaN layer. 19 Park et al demonstrated the ohmic property of graphene on Al x Ga 1−x N/GaN by inserting a monolayer graphene between the Cr metal and the AlGaN/GaN semiconductor. 18 Fisichella et al compared the contact properties of graphene in terms of surface roughness and defectivity.…”

Current-Temperature Scaling for a Schottky Interface with Nonparabolic Energy Dispersion

“…For simplicity, we assume that ∆Φ (N ) i is the same as the work function difference between monolayer graphene and FLG, which has a typical value of ∆Φ ABC ≈ 0.93 where Φ fit is the Schottky barrier height fitted from the Arrhenius plot assuming a T 2 scaling. It should be noted that the good agreement between the T 2 -fitted and the actual values of Φ [4,[12][13][14][15][16][17][18][19] could misleadingly suggest the conventional T 2 model as a valid model for Schottky interfaces composed of non-parabolic energy dispersions. We summarize the main findings of this article in Table I.…”

Recent advances in wide bandgap semiconductor-based gas sensors

“…The high electron sheet carrier concentration of nitride HEMTs is induced by piezoelectric polarization of the strained AlGaN layer and the spontaneous polarization is considerable in wurtzite III-nitrides. This provides an increased sensitivity relative to simple Schottky diodes fabricated on GaN layers (Baranzahi et al, 1995;Luther et al, 1999;Schalwig et al, 2001;Schalwig et al, 2002a;Kim et al, 2003;Weidemann et al, 2003;Kim et al, 2003b;Kang et al, 2004a;Kang et al, 2004b;Kouche et al, 2005;Matsuo et al, 2005;Voss et al, 2005;Wang et al, 2005;Yun et al, 2005;Song et al, 2005a;Song et al, 2005b;Ali et al, 2006;Huang et al, 2006). The gate area can be functionalized so that current changes can be detected for a variety of gases, liquids and biomolecules.…”