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

This study utilizes a metalorganic chemical vapor deposition system to grow a β‐Ga2O3 epitaxial layer on a sapphire substrate and fabricate lateral β‐Ga2O3 metal‐oxide‐semiconductor field‐effect transistors (MOSFETs). To enhance the performance of the β‐Ga2O3 MOSFET, a (AlxGa1‐x)2O3 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 (AlxGa1‐x)2O3 layers containing different Al compositions, specifically (Al0.14Ga0.86)2O3 and (Al0.21Ga0.79)2O3. The influence of the Al composition in the (AlxGa1‐x)2O3 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 (ID,sat) from 2.94 to 7.88 mA mm−1—a significant 168% improvement in the (AlxGa1‐x)2O3/β‐Ga2O3 stacked epitaxy structure. For the high‐Al‐composition barrier layer ((Al0.21Ga0.79)2O3), 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‐Ga2O3/(AlxGa1‐x)2O3 interface, which reduced the leakage current density. By optimizing the Al composition in (AlxGa1‐x)2O3, transistors suitable for either high performance or high breakdown voltage are successfully produced.