Effect of the AlGaO Spacer Layer on the Performance of β‐Gallium Oxide Metal–Oxide Semiconductor Field Effect Transistors

Abstract This study utilizes a metalorganic chemical vapor deposition system to grow a β‐Ga 2 O 3 epitaxial layer on a sapphire substrate and fabricate lateral β‐Ga 2 O 3 metal‐oxide‐semiconductor field‐effect transistors (MOSFETs). To enhance the performance of the β‐Ga 2 O 3 MOSFET, a (Al x Ga 1‐x ) 2 O 3 spacer layer is introduced, with its aluminum (Al) composition modulated through energy band engineering. Three epitaxial samples are designed: a reference sample (without a spacer layer) and samples with (Al x Ga 1‐x ) 2 O 3 layers containing different Al compositions, specifically (Al 0.14 Ga 0.86 ) 2 O 3 and (Al 0.21 Ga 0.79 ) 2 O 3 . The influence of the Al composition in the (Al x Ga 1‐x ) 2 O 3 layer on the two dimensional electron gas (2DEG) is investigated. The results show that a lower Al composition increases the carrier concentration in the 2DEG, boosting the saturation current (I D,sat ) from 2.94 to 7.88 mA mm −1 —a significant 168% improvement in the (Al x Ga 1‐x ) 2 O 3 /β‐Ga 2 O 3 stacked epitaxy structure. For the high‐Al‐composition barrier layer ((Al 0.21 Ga 0.79 ) 2 O 3 ), the higher energy barrier slightly reduces the turn‐on current but effectively increases the breakdown voltage, from 210 to 576 V—an improvement of 188%. These improvements result from the higher energy barrier of the β‐Ga 2 O 3 /(Al x Ga 1‐x ) 2 O 3 interface, which reduced the leakage current density. By optimizing the Al composition in (Al x Ga 1‐x ) 2 O 3 , transistors suitable for either high performance or high breakdown voltage are successfully produced.