Electrical Characterization of GaN on SiC HEMT Wafer

In frontier research on RF and power electronic devices, the intrinsic electrical parameters of epitaxial wafers—particularly the transport properties of the two-dimensional electron gas (2DEG)—directly determine the frequency response, output current density, and reliability margins of the resulting devices. For universities and research institutes, epitaxial materials must not only meet design specifications but also provide quantifiable full-wafer uniformity, traceable batch-to-batch variation, and reproducible test methodologies, thereby supporting mechanism studies, device modeling, and process optimization.

This article takes SiC-based GaN HEMT epitaxial wafers as an example to systematically describe their core electrical characterization parameters and test methods, and presents typical measured uniformity data, aiming to provide researchers with a reference for material selection and quality assessment.

1. Substrate Selection and Epitaxial Structure Design

SiC substrates, with a thermal conductivity of ~490 W/(m·K) and a lattice mismatch with GaN of approximately 3.5%, offer irreplaceable heat-dissipation advantages in high-power RF applications. Taking a 4‑inch SiC‑based GaN HEMT epitaxial wafer as an example, the typical layer structure is as follows. The introduction of the AlN insertion layer enhances polarization discontinuity and significantly improves 2DEG mobility, while the graded composition and thickness design of the buffer layer serves to reduce threading dislocation density—an aspect of considerable importance for studies on breakdown voltage and interface state density.

Epitaxial Layer	Thickness
AlGaN barrier layer	*
AlN insertion layer	*
u‑GaN channel layer	*
Buffer layer (multi‑layer graded)	*
SiC substrate	510 μm

 

Full‑wafer multi‑point uniformity results:

Fig. 1 Sheet resistance and Hall coefficient at multiple test sites on a 4‑inch GaN‑on‑SiC epitaxial wafer

Fig. 2 Mobility and carrier sheet density at multiple test points on a 4‑inch GaN‑on‑SiC epitaxial wafer

PAM-XIAMEN supports customization of AlGaN barrier thickness, Al composition, AlN insertion layer thickness, and buffer layer structure schemes to meet the experimental design requirements of specialized research topics such as polarization engineering, stress regulation, or reliability physics, and, by combining precision MOCVD growth processes with comprehensive Hall characterization, provides epitaxial solutions that not only meet design targets but also are accompanied by fully traceable data documentation, thereby facilitating innovative development of high‑efficiency RF devices and power modules. For further details, please contact: [email protected].

2. Key Electrical Parameters and Their Physical Implications

For AlGaN/GaN heterojunctions, Hall-effect measurements yield four core output quantities, each corresponding to distinct physical mechanisms and device implications:

• Sheet resistance (Ω/sq): Reflects the conductivity of the 2DEG and is directly related to the on‑resistance. Its full‑wafer uniformity (standard deviation/mean) serves as a sensitive indicator for assessing the stability of growth temperature and gas flow distributions.
• Hall coefficient (m³/C): The sign indicates the carrier type (negative for electrons), and its absolute value, combined with the magnetic field and current, can independently verify the sheet density magnitude, aiding in distinguishing contributions from parallel conducting layers (e.g., buffer leakage).
• Mobility (cm²/(V·s)): The most widely regarded material quality criterion, governed by interfacial roughness, alloy disorder, and phonon scattering. In temperature‑dependent Hall measurements, the mobility‑temperature relationship can further be used to identify the dominant scattering mechanism.
• Carrier sheet density (cm⁻²): Determined by the Al composition, thickness, and polarization strength of the AlGaN layer, it directly affects the maximum saturation current and transconductance of the device.

3. Test Methods: Van der Pauw and In‑Line Non‑Contact Hall

The Van der Pauw method is conventionally employed as the standard characterization technique within the industry, performing at least eight current‑voltage combinations on four ohmic contacts to eliminate contact resistance effects and accurately extract sheet resistance and Hall coefficient. This method has been validated by international semiconductor standards and is suitable for precise transport analysis of heterojunction thin‑film materials.

For batch inspection needs, non‑contact microwave‑reflection Hall measurement is used as a supplementary approach, enabling rapid, nondestructive measurement of sheet resistance, mobility, and carrier concentration across the wafer, with a measurement range covering 100–20000cm²/(V·s), making it ideal for rapid feedback during process development iterations.

Whether you need GaN epitaxial wafer for research or for industrial applications, please contact us email at [email protected] and [email protected].

 

Reference:

Qiao, D., Ni, X., Fan, Q., & Gu, X. (2025). An Improved Fabrication Method for Van Der Pauw Mobility Measurement on GaN Epitaxy on Conductive and Non-Conductive Substrates. Coatings, 15(4), 491.