Defect Metrology and Charge Trapping Dynamics in Transfer-Doped Diamond Transistors

Hydrogen-terminated (surface-channel) diamond transistors hold great promise for next-generation, high-frequency, high-power RF electronics and advanced communications due to diamond's high breakdown field and superior thermal conductivity. However, wide-scale operational deployment is constrained by "current collapse" and "knee walkout" - phenomena where transient charges trapped at defect sites in the semiconductor prevent the transistor from operating at its full, high-frequency RF power. Commercial device-characterization tools, built primarily for silicon or traditional compound semiconductor materials, lack the specialized physics and sensitivity required to isolate and characterize traps in ultra-wide bandgap (UWBG) diamond devices. These performance-limiting charge traps can reside in multiple distinct, critical locations within the device stack, including the gate dielectric, the dielectric-to-diamond interface, the diamond epitaxial layer, the epitaxial-to-substrate interface, and the diamond bulk substrate. Understanding and mitigating these mechanisms requires a specialized metrology capability. This topic seeks the development of a comprehensive measurement system and associated methodology capable of extracting trap density, energy levels, physical location (specifically identifying the layers or interfaces where the traps reside), and time constants characterizing these defects so that design teams can efficiently work to address them. Standard capacitance-voltage (CV) or simple transient electrical analyses do not provide sufficient physical insight into trap dynamics. Specifically, a successful technique and system must be capable of resolving multiple trap populations and correlating these distinct signatures with observed current collapse behavior in diamond. Because hydrogen-terminated diamond relies on unique surface-channel p-type conduction, validation of these new techniques can not necessary rely on prior validation from conventional n-type semiconductor materials (e.g., GaN, Ga2O3, AlN), as the fundamentally different physical mechanisms and device architectures may not be acceptable surrogates for the diamond device behavior. To meet operational requirements, all primary experimental validations and core metrology capability demonstrations under this effort must be performed specifically on Government-provided hydrogen-terminated diamond material and RF transistor devices. The Government will provide these verified working devices and/or test articles as Government Furnished Property (GFP) during the execution phase to anchor the research. The public literature contains examples of hydrogen-terminated diamond RF transistors that exhibit comparable baseline characteristics [1, 2]. While the GFP will vary in specific design, architecture, and properties from the literature, they can provide a baseline for concept development. It is expected that preliminary or intermediate metrology demonstrations on other wide or ultra-wide bandgap semiconductor devices may be used for initial development, the main and final capability demonstrations must be validated directly on the specific diamond device architectures provided. This effort will address a critical metrology gap, establishing a validated metrology standard that accelerates the development of high-reliability diamond RF electronics.