Ultra-Thin Barrier Enhancement-Mode InAlN/GaN HEMTs on Sapphire Substrate with a DIBL of 5.2 mV/V

Gallium nitride (GaN) materials provide excellent characteristics for high-power and high-frequency devices with low on-resistance (Ron) owing to their high-mobility two-dimensional electron gas (2DEG) and wide bandgap. Due to the strong spontaneous and piezoelectric polarization in GaN heterojunction, 2DEG exhibits conductivity even when no gate voltage is applied. Consequently, depletion-mode (D-mode) high electron mobility transistors (HEMTs) can be naturally achieved; however, achieving enhancement-mode (E-mode) HEMTs can take time and effort. It is worth mentioning that E-mode HEMTs only need to operate with a single positive polarity, which simplifies circuit design by removing the requirement for a negative bias voltage. Thus, E-mode HEMTs have the advantage of decreasing the intricacy, power usage, and processing expenses of GaN systems, making them the preferable choice for RF systems. The gate recess technique, which has drawbacks such as complex process stages, interface degradation, and instability in threshold voltage, is frequently employed to create E-mode HEMTs. This study successfully produced recess-free E-mode HEMTs on a sapphire substrate using an ultra-thin barrier (UTB) structure, resulting in the natural depletion of 2DEG. PECVD SiN passivation effectively restores the 2DEG in the access region while protecting devices, considerably reducing Ron. The E-mode HEMTs showed a threshold voltage of +0.5V, a Drain Induced Barrier Lowering (DIBL) of 5.2 mV/V, an an I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</inf>/I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</inf> ratio of 4×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup>, and a maximum current/power gain cut-off frequency (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf>/f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf>) of 37/123 GHz. The exceptionally low drain-induced barrier lowering (DIBL) indicates that the devices possess a consistent threshold voltage, and the UTB construction shows promising potential for reducing the impact of short-channel effects. UTB E-mode HEMTs offer advantages in simplifying the manufacturing process, enabling significant scalability, and delivering excellent high-frequency performance.