Forward and reverse current transport mechanisms in tungsten carbide Schottky contacts on AlGaN/GaN heterostructures

Abstract

In this paper, the forward and reverse current transport mechanisms in as-deposited and 400 °C annealed tungsten carbide (WC) Schottky contacts on AlGaN/GaN heterostructures have been studied. In particular, under forward bias, the WC/AlGaN Schottky contacts exhibited a deviation from the ideal thermionic emission model due to the occurrence of a tunneling component of the current. From the temperature dependence of the ideality factor, a characteristic tunneling energy E00 in the range of 33–36 meV has been estimated. On the other hand, two different transport mechanisms have been identified under reverse bias. At low reverse bias (VR < 2 V), Poole–Frenkel emission rules the current transport, with an emission barrier ϕt = 0.68 eV in the as-deposited contact, which increases up to ϕt = 0.79 eV upon annealing at 400 °C. This behavior has been correlated with the improvement of the metal/AlGaN electronic properties. At higher reverse bias (VR > 2 V), the leakage current is dominated by a thermally activated process with an activation energy (0.27 eV) that is independent of the Schottky contact fabrication process. In this case, the temperature dependence of the leakage could be well described by a two-dimensional variable range hopping conduction associated with the presence of surface defects in the material.

Highly Homogeneous 2D/3D Heterojunction Diodes by Pulsed Laser Deposition of MoS2 on Ion Implantation Doped 4H‐SiC

“…where the voltage dependence is formally identical to the one for TE (Equation ( 1)), by expressing the characteristic energy E 0 as E 0 = nk B T/q. From this analogy, the temperature dependence of the ideality factor determined in Figure 4d can be described as [46] :…”

“…This mechanism is further supported by the temperature dependence of n. In fact, the current‐voltage curves in the TFE processes can be expressed as: $$\[ \begin{array}{*{20}{c}}{{J_{{\rm{TFE}}}} = {J_{{\rm{s,TFE}}}}\,{e^{\frac{{qV}}{{{E_0}}}}}}\end{array} \]$$where the voltage dependence is formally identical to the one for TE (Equation ()), by expressing the characteristic energy E 0 as E 0 = nk B T/q. From this analogy, the temperature dependence of the ideality factor determined in Figure 4d can be described as [ 46 ] : $$\[ \begin{array}{*{20}{c}}{n = \frac{{q{E_0}}}{{{k_B}T}} = \frac{{q{E_{00}}}}{{{k_B}T}}\coth \left( {\frac{{q{E_{00}}}}{{{k_B}T}}} \right)}\end{array} \]$$where the energy E 00 depends on the surface donors concentration N D of n + doped 4H‐SiC as [ 35,45 ] : $$\[ \begin{array}{*{20}{c}}{{E_{00}} = \frac{h}{\pi }\sqrt {\frac{{{N_D}}}{{{{\rm{m}}_{{\rm{eff}},\,{\rm{SiC}}}}{\varepsilon _0}{\varepsilon _{{\rm{SiC}}}}}}} }\end{array} \]$$being m eff,SiC = 0.42 m 0 the effective mass and ε SiC = 9.6 the relative permittivity of 4H‐SiC, respectively. By fitting the temperature dependence of n on T for MoS 2 diodes on n + ‐SiC with Equations ()–(), as shown in Figure 4d, a value of N D ≈1 × 10 19 cm −3 is obtained.…”

Trap-mediated bipolar charge transport in NiO/Ga2O3 p+-n heterojunction power diodes

“…At high biases, the reverse current density shows a weak bias dependence, which was also observed in AlGaN [35], GaN [36], and Ga 2 O 3 [10,34]based devices and has been widely accepted as the contribution of Poole-Frenkel emission (PFE). Furthermore, PFE has been also reported to govern the current transport in the AlGaN/GaN heterostructure at low reverse biases [37]. PFE can be considered as the field-enhanced thermal excitation of carriers from the trap states into the continuum of electronic states, e.g., conduction band, which can be expressed as [34,35,37] ( )…”

“…Furthermore, PFE has been also reported to govern the current transport in the AlGaN/GaN heterostructure at low reverse biases [37]. PFE can be considered as the field-enhanced thermal excitation of carriers from the trap states into the continuum of electronic states, e.g., conduction band, which can be expressed as [34,35,37] ( )…”

Current transport in Ni Schottky barrier on GaN epilayer grown on free standing substrates

“…In wide band gap semiconductors, the thermionic Field Emission theory has been often used to explain the reverse J-V characteristic in Schottky Diodes [27,28,29]. The experimental J-V curves (at 25, 75 and 125°C) are reported together with those calculated using the thermionic field emission model (TFE) [30].…”