Optimization of enhancement-mode MIS-GaN HEMT with dual channel for simple process using TCAD simulation

Area of Science:

• Semiconductor Physics
• Materials Science
• Device Engineering

Background:

• Gallium Nitride (GaN) high electron mobility transistors (HEMTs) are crucial for high-power and high-frequency applications.
• Achieving enhancement-mode (E-mode) operation in GaN HEMTs is essential for simplified circuit design and reduced power consumption.
• Current E-mode fabrication methods, such as recessed gates or p-GaN gates, involve complex and precise processing steps.

Purpose of the Study:

• To demonstrate a novel metal-insulator-semiconductor (MIS) dual-channel HEMT (IDC-HEMT) structure for achieving E-mode operation.
• To investigate the impact of the dual-channel structure on the transistor's electrical characteristics, particularly the threshold voltage (Vth).
• To confirm the feasibility of E-mode operation without resorting to intricate fabrication techniques.

Main Methods:

• Utilizing the Synopsys Sentaurus™ technology computer-aided design (TCAD) simulator for device modeling and simulation.
• Designing a dual-channel structure with two AlGaN/GaN heterojunction layers to form two distinct two-dimensional electron gas (2DEG) layers.
• Analyzing the electron dynamics and charge distribution within the dual-channel structure to understand the mechanism for E-mode operation.

Main Results:

• The proposed MIS dual-channel HEMT (IDC-HEMT) successfully achieved E-mode operation with a threshold voltage (Vth) of 0.25 V, a significant positive shift of 1.66 V compared to a single-channel device.
• The 2DEG sheet densities were measured: 5.49 × 10^12 cm^-2 (upper channel, single-channel HEMT), 3.43 × 10^12 cm^-2 (upper channel, dual-channel HEMT), and 0.76 × 10^12 cm^-2 (lower channel, dual-channel HEMT).
• The IDC-HEMT exhibited a slightly increased on-resistance (R_on) of 28.7 Ω·mm compared to the single-channel HEMT's 22.7 Ω·mm, attributed to the reduced 2DEG density in the upper channel.

Conclusions:

• The dual-channel structure effectively induces a negative bias body effect, enabling a positive shift in threshold voltage for E-mode operation.
• This IDC-HEMT design offers a viable alternative for achieving E-mode GaN HEMTs, circumventing the need for complex etching processes.
• The results confirm the potential of the dual-channel approach for developing simpler and more efficient E-mode GaN power devices.