GaN Gate Stack with Composite Doping for Threshold Control

The patent applies local quality by creating different gate structures with specific doping configurations in different regions of the semiconductor device. Enhanced mode transistors receive gates with one doping configuration while depletion mode transistors receive gates with another configuration, allowing each region to have optimized properties for its specific function. This is achieved through selective doping processes that modify local electrical characteristics without affecting other regions.

The gate formation process is segmented into multiple discrete steps including selective doping, epitaxial growth, and patterned etching. Each step is independently controlled to achieve the desired threshold voltage characteristics for different transistor types. The gate structure itself is segmented into regions with different doping concentrations and compositions, allowing independent optimization of E-mode and D-mode device characteristics.

The patent employs parameter changes by systematically varying doping concentrations, layer thicknesses, and material compositions to achieve precise control over threshold voltage. Different doping levels (e.g., 1e18 to 1e20 atoms/cm³), layer thicknesses (e.g., 5nm to 50nm), and material compositions (AlGaN with varying Al content) are used to tune the electrical characteristics of each gate structure for its intended function.

The gate structures utilize composite materials consisting of multiple semiconductor layers with different compositions and properties. The gate comprises stacked layers including doped GaN, AlGaN, and undoped GaN layers, each contributing specific electrical characteristics. This composite structure enables fine-tuned control of threshold voltage and carrier concentration that cannot be achieved with single-material gates.