Space-charge-limited current flow in gallium nitride thin films

Polycrystalline gallium nitride (GaN) thin films, 1-5 {μ} thick, were deposited on degenerate silicon (Si) substrates by reactive rf sputtering at 45 ^∘{}C. The resulting electrical characteristics are interpreted in terms of space-charge-limited current flow in the presence of two discrete trap levels. Analysis of the data indicates an equilibrium electron concentration of 5.2×{}10³-7.8×{}10⁴ cm^-3, carrier mobility of 330 cm²/V sec, and density of traps located 0.81 and 0.39 eV below the conduction band edge of 3.7×{}10¹⁴ and 1.9×{}10¹⁹ cm^-3, respectively. The effect of post-heat treatments in a continuous nitrogen gas flow is shown to decrease the carrier mobility and increase the concentration of shallow traps while maintaining the density of the deeper traps approximately constant. At large electric fields (E>4×10⁵ V/cm), a hot-electron effect is shown to be dominant.