Metal-induced gap states and Schottky barrier heights at nonreactive GaN/noble-metal interfaces

Abstract

We present ab-initio local density FLAPW calculations on non-reactive Nterminated [001] ordered GaN/Ag and GaN/Au interfaces and compare the results (such as metal induced gap states and Schottky barrier heights) with those obtained for GaN/Al, in order to understand the dependence of the relevant electronic properties on the deposited metal. Our results show that the density of gap states is appreciable only in the first semiconductor layer close to the interface. The decay length of the gap states in the semiconductor side is about 2.0 ± 0.1Å and is independent of the deposited metal, therefore being to a good extent a bulk property of GaN. Our calculated values of the Schottky barrier heights are Φ Bp (GaN/Ag) = 0.87 eV and Φ Bp (GaN/Au) = 1.08 eV; both values are smaller than the GaN/Al value (Φ Bp (GaN/Al) = 1.51 eV) and this quite large spread of values excludes the possibility of a Fermi level pinning within the GaN band gap. Because of the low screening in GaN, the potential barrier at the junction is strongly affected by the structural arrangement of the first metal layer at the interface. This leads to quite large variations of the Schottky barrier height as a function of the metal, in contrast with the behavior of GaAs/metal interfaces.

Ab initio study of interface states and Schottky barriers at metal contacts to GaN(001)

“…The corresponding p-type SBHs are shown in Table 1. Taking into account that our calculations are performed with soft pseudopotentials, our results are reasonably close to theoretical values, obtained with FLAPW calculations [9].…”

“…SBH (This work) SBH (from [9]) Au/GaN(001) 0.82 eV 1.08 eV Cu/GaN(001) 1.00 eV Al/GaN(001) 1.68 eV 1.51 eV The differences in the resulting Schottky barrier heights to those of [9] can be attributed to two reasons: the different treatment of core electrons (pseudopotentials versus all-electron potentials) and the neglect of spin-related phenomena in our calculations. These effects are expected to be more important for heavier atoms like Au than for lighter ones like Al: while the epitaxial geometry for the Al/GaN(001) used in this work is identical to that of [9], the equilibrium interfacial distance differ for Au/GaN (d 0 =1.40Å[this work] versus d 0 =1.34Å [9].…”

“…These effects are expected to be more important for heavier atoms like Au than for lighter ones like Al: while the epitaxial geometry for the Al/GaN(001) used in this work is identical to that of [9], the equilibrium interfacial distance differ for Au/GaN (d 0 =1.40Å[this work] versus d 0 =1.34Å [9]. The Schottky barrier depends highly on the interfacial distance.…”

The physics and chemistry of the Schottky barrier height

“…The type of silicide interfaces, e.g., 8-fold or 6-fold, described above is a subtle example of this termination issue. For every compound semiconductor studied by numerical calculations, termination at polar interfaces has been a prominent parameter that leads to different SBHs, e.g., for GaAs(100), 39 GaN(100), 101 and ZnSe (100) 87 interfaces. General considerations would suggest that, everything else being equal, the anion-terminated interface should have a smaller n-type SBH than the one terminated on cations.…”

Schottky barrier formation at the Au to rare earth doped GaN thin film interface

“…Surface alloying can occur [14] and a large range of experimentally measured Schottky barrier heights has been reported (0.76-1.40 eV) at the Au to n-type GaN interface [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], using photoemission spectroscopy (PES), current-voltage (I-V) and capacitance voltage (C-V) characteristics, and internal photoemission [30]. However, the generally accepted value is about 1.08 eV [31]. Kurtin et al [32] suggested that the Schottky barrier height on GaN should depend directly on the work function or electronegativity difference between the metal electrode and GaN.…”