Effect of Insertion of Ultrathin Al₂O₃ Interlayer at Metal/GaN Interfaces

Abstract

Fermi level depinning at a metal/semiconductor interface by using an ultrathin insulating interlayer to block the penetration of the metal wave function into the semiconductor is examined on GaN. A Si‐doped n‐type GaN epitaxial layer on a freestanding GaN substrate is used as the host material. For the samples with an interlayer, an ultrathin Al2O3 layer of 1 nm thickness is deposited by atomic layer deposition. As the metal layers, Ag, Cu, Au, Ni, and Pt are deposited by electron beam evaporation. Samples without an interlayer are also fabricated for comparison. The apparent change in current–voltage characteristics of the Schottky barrier diodes with the insertion of the interlayer is dependent on the electrode metal. However, the apparent Schottky barrier height (SBH) for the samples with the interlayer is almost constant and independent of the metal electrode, although the samples without an interlayer exhibit a moderate dependence of the SBH on the metal work function. Thus, the pinning becomes stronger upon the insertion of the interlayer, although blocking of the metal wave function by using an ultrathin insulator is expected to lead to depinning.

Effects of surface treatment on Fermi level pinning at metal/GaN interfaces formed on homoepitaxial GaN layers

“…Fermi level pinning at metal/GaN interfaces for this layer. Indeed, the ϕB-ϕM relation has been newly reported [20][21][22] .…”

Annealing‐Free Ohmic Contacts to n‐Type GaN via Hydrogen Plasma‐Assisted Atomic Layer Deposition of Sub‐Nanometer AlOx

“…[ 46 ] However, for a 1 nm thin Al 2 O 3 interlayer grown by thermal ALD, slightly increased FLP (decreased S ) was previously observed. [ 20 ] Similarly, the HP/TMA ALD process investigated here results in increased FLP ( S = 0.08 ± 0.07). This near‐total Fermi level pinning cannot be described by the MIGS model but can instead be ascribed to high concentrations of defects with localized energy distributions at the interface.…”

“…They hypothesized that the surface passivation reduces Fermi level pinning, lowering the Schottky barrier height between GaN and the low work function metal Yb (Φ Yb = 2.6 eV). In contrast, Akazawa et al [20] found that Fermi level pinning increases upon inserting a 1 nm thin Al 2 O 3 interlayer at GaN/metal interfaces. Additional insight into the nature of this interface comes from the observation that thermal ALD of Al 2 O 3 monotonically reduces GaN surface band bending with increasing Al 2 O 3 thickness.…”

“…In contrast, Akazawa et al. [ 20 ] found that Fermi level pinning increases upon inserting a 1 nm thin Al 2 O 3 interlayer at GaN/metal interfaces. Additional insight into the nature of this interface comes from the observation that thermal ALD of Al 2 O 3 monotonically reduces GaN surface band bending with increasing Al 2 O 3 thickness.…”

Barrier reduction and current transport mechanism in Pt/n-InP Schottky diodes using atomic layer deposited ZnO interlayer

“…AlN IL has been studied as a passivation layer for GaN-based power devices [21]. Akazawa and Hasezaki utilized a 1 nm thick Al 2 O 3 IL in metal/ GaN Schottky diodes and observed the increased barrier height with a Al 2 O 3 IL [22]. However, they also observed that it became almost independent of the metal work function, although FL depinning by blocking metal wave function was expected.…”