Barrier Strain and Carbon Incorporation-Engineered Performance Improvements for AlGaN/GaN High Electron Mobility Transistors**

The improvements in electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) grown using metal-organic (MO)CVD by engineering structure, barrier strain, and unintentional carbon incorporation, are demonstrated in this work. Both normal HEMT structure (with a high temperature (HT) AlN buffer) and advanced HEMT structure (with a high-low-high temperature (HLHT) AlN buffer, and a HT AlN interlayer (IL)) present a breakdown voltage higher than 200 V, while a much smaller breakdown voltage of 17 V is measured on the conventional structure using a low-temperature GaN buffer. The HT AlN IL inserted in the middle of the conventional HEMT structure introduces a reduction in the tension of the AlGaN barrier, which results in an improvement of the surface morphology (0.46 nm). As a consequence, the two-dimensional electron gas (2DEG) mobility increases by remarkable 46% (1900 cm² V⁻¹ s⁻¹). The HLHT AlN buffer, substituting for the HT AlN buffer, leads to the enhancement of GaN crystalline quality, which contributes to the performance improvement for HEMTs. The advanced HEMT, using both an AlN IL and an HLHT AlN buffer, produces increases in the DC maximum drain current by 35.5% (∼680 A mm⁻¹), and in the transconductance by 15% (114 mS mm⁻¹) in comparison with the normal HEMT with an AlN buffer. The very low leakage current in the advanced HEMTs is caused by optimizing the design of the buffer and modifying growth parameters. Lastly, the reduction of AlGaN barrier tensile strain by inserting the HT AlN IL is promising for an improvement in AlGaN/GaN HEMT reliability.