Size effect on high temperature variable range hopping in Al⁺ implanted 4H-SiC.

Area of Science:

• Materials Science
• Semiconductor Physics

Background:

• Understanding charge transport in heavily doped semiconductors is crucial for device performance.
• Aluminum-doped 4H-Silicon Carbide (4H-SiC (Al)) is a key material for high-power electronics.

Purpose of the Study:

• To analyze the hole transport properties of heavily doped 4H-SiC (Al) layers.
• To determine the dominant transport mechanisms as a function of doping concentration and annealing.
• To investigate the influence of structural defects on charge transport.

Main Methods:

• Electrical characterization of 4H-SiC (Al) layers with varying aluminum concentrations (3x10^20 to 5x10^20 cm^-3) and annealing temperatures (1950-2100 °C).
• Analysis of resistivity and conductivity temperature dependence to identify transport mechanisms.
• Transmission Electron Microscopy (TEM) for structural investigation of implanted layers.

Main Results:

• Variable Range Hopping (VRH) into an impurity band explains the temperature dependence of resistivity.
• Two distinct VRH regimes were identified: isotropic 3D VRH and anisotropic nearly 2D VRH.
• Anisotropic 2D VRH, observed in heavily doped samples, correlates with the presence of basal plane stacking faults (SFs), with SF separation matching VRH hopping lengths.

Conclusions:

• The transport mechanism in heavily doped 4H-SiC (Al) is strongly influenced by doping levels and annealing, leading to VRH.
• Basal plane stacking faults significantly contribute to anisotropic 2D VRH transport in thick implanted layers.
• 3D Nearest Neighbor Hopping (NNH) is observed in lightly doped samples without detectable SFs.