Doped Diamond for Light-Triggered Electronics

Doped Diamond for Light-Triggered Electronics Doped Diamond for Light-Triggered Electronics Diamond is often considered the ideal semiconductor for high power electronics. The 5.45 eV bandgap sustains a breakdown field of > 10 MV/cm, the high electron and hole mobilities (4,500 cm2/V-s for electrons and 3,800 cm2/V-s for holes) provides low resistance, and the highest thermal conductivity (22 W/cm-K) sustains high current density. Moreover, for optically excited carriers the indirect bandgap provides a long carrier lifetime. This study will develop plasma CVD processes to deposit phosphorus or nitrogen doped epitaxial diamond layers on transparent substrates appropriate for optical switching characterization at LLNL. Co-doped phosphorus-nitrogen doped layers will also be demonstrated. The goal of the project is to provide layers of sufficient thickness and of different uniform doping density to determine optical excitation efficiencies (at LLNL). Optical grade single crystal substrates will be employed to enable optical testing with minimal uncontrolled background excitation from defects and impurities. A challenge will be achieving controlled and uniform doping concentration for layers up to 10 m thick. The dopant incorporation efficiency strongly depends on the crystallographic surface and surface faceting during growth can lead to lateral and vertical dopant non-uniformities. A research goal will be to establish plasma conditions to minimize faceting during growth and enable controlled and uniform doping with concentrations in the range of 5E17 to 5E19 cm-3. Diamond epitaxial layers will be fabricated using the ASU Diamond Materials Lab. Figure 1 presents a schematic of the diamond growth process, and pictures of the microwave plasma growth chamber and the sample configuration. Diamond growth is achieved with ~ 1% methane in hydrogen. The gas phase precursors for boron, phosphorus or nitrogen doped layers are trimethylborane (TMB), trimethylphosphine (TMP), or nitrogen, respectively. The growth is monitored with an emission spectrometer and a dual wavelength optical pyrometer. In this project, (100) and (111) oriented diamond plates will be purchased and used for substrates. The CVD substrates can have low impurity densities often < 1016 cm-3 with threading dislocation densities of ~105 per cm3. The high pressure, high temperature substrates have impurity levels often > 1016 cm-3 level but with threading dislocation densities <103 per cm3. The diamond epitaxial layers will be characterized using SIMS for dopant concentration, and photoluminescence to establish the impurity configuration and lateral uniformity. The research milestones include: Demonstrate epitaxial layers (1-10m) with N doping levels from 5 E17 to >1 E19 cm-3. Characterize doping with SIMS and photoluminescence. Provide substrates for optical characterization. Demonstrate epitaxial layers (1-10m) with P doping levels from 5 E17 to >1 E19 cm-3. Characterize doping with SIMS. Provide substrates for optical characterization. Demonstrate epitaxial layers (1-10m) with N and P co-doping. Characterize doping with SIMS and photoluminescence. Provide substrates for optical characterization.