Metal Contacts on a-GaN

Abstract

The Schottky barrier heights of silver and lead contacts on n-type GaN (0001) epilayers were determined from current-voltage characteristics. The zero-bias barrier heights and the ideality factors were found to be linearly correlated. Similar observations were previously reported for metal contacts on Si (111) and GaAs (110) surfaces. The barrier heights of ideal Schottky contacts are characterized by image force lowering of the barrier only. This gives an ideality factor of 1.01. From our data we obtain barrier heights of 0.82 eV and 0.73eV for ideal Ag and Pb contacts on GaN, respectively. The metal-induced gap states (MIGS) model predicts the barrier heights of ideal Schottky contacts on a given semiconductor to be linearly correlated with the electronegativities of the metals. The two important parameters of this MIGS-and-electronegativity model are the charge neutrality level (CNL) of the MIGS and a slope parameter. The CNL may be calculated from the dielectric band gap and using the empirical tight-binding method. The slope parameters are given by the optical dielectric constant of the respective semiconductor. The predictions of the MIGS model for metal/GaN contacts are confirmed by the results presented here and by barrier heights previously reported by others for Au, Ti, Pt, and Pd contacts on GaN.

Metal/GaN Contacts Studied by Electron Spectroscopies

“…The final Schottky barrier height of Cu/GaN and Au/GaN measured by XPS is 0.84eV and 1.15eV respectively. These values are close to results (0.82eV and 0.96eV) from the MIGS and electronegativity model using values for S χ and Φ cnl calculated by Kampen and Mönch [1]. These authors measured and calculated a barrier height of 0.82 eV for Ag/GaN, which is close to our result for Cu/GaN.…”

“…They were calculated by Kampen and Mönch [1] who obtained S χ = 0.29 eV/Miedema-unit. and Φ cnl = 2.35 eV with respect to the top of the valence band.…”

Structural and electronic properties of ideal nitride/Al interfaces

“…40͒ and GaN, 41,42 we find that we should add to our ⌽ B p values shown in Table II a 47 which focuses on the electronegativity of the metal, predicts that all the ideal ͑i.e., abrupt, defect free, and laterally homogeneous͒ metal/n-doped GaN contacts should be rectifying. 48 In particular, according to this model 47 and using empirical tight binding calculations, 49 we should have a potential barrier ⌽ B n ϳ 0.8 eV ͑or equivalently ⌽ B p ϳ 2.6 eV͒ in the GaN/Al case. The predictions of the latter model 47,48 are in better qualitative agreement with our findings than the Schottky-Mott rule, but there still is an appreciable discrepancy with our ab initio calculated value (⌽ B p LDA ϭ1.22 eV͒.…”

“…48 In particular, according to this model 47 and using empirical tight binding calculations, 49 we should have a potential barrier ⌽ B n ϳ 0.8 eV ͑or equivalently ⌽ B p ϳ 2.6 eV͒ in the GaN/Al case. The predictions of the latter model 47,48 are in better qualitative agreement with our findings than the Schottky-Mott rule, but there still is an appreciable discrepancy with our ab initio calculated value (⌽ B p LDA ϭ1.22 eV͒.…”

Characterization of AlGaN-Schottky Diodes Grown by Plasma Induced Molecular Beam Epitaxy

“…Therefore, the barrier heights of our Pt-and Pd±GaN contacts are plotted in Fig. 2 versus their ideality factor [14]. For homogeneous metal±semiconductor contacts the barrier height is lowered due to the image force and becomes voltage dependent.…”