Characterization of high-quality polycrystalline diamond and its high FET performance

We characterized high-quality polycrystalline diamond with large grains and fabricated polycrystalline diamond field effect transistors (FETs). The polycrystalline diamond had (110) preferred orientation, and its typical grain size was  100 μm. Well-resolved free exciton related emissions were observed at room temperature in cathodoluminescence. The FETs showed extremely high DC and RF performance. The cut-off frequency for current gain (f_T) and power gain (f_max) were 45 and 120 GHz, respectively. The maximum drain current (I_DS) was 550 mA/mm. These values are the highest among diamond FETs, including those fabricated from single-crystal diamond. These results suggest that high-quality polycrystalline diamond, whose maximum size is 4 in., is very promising for diamond electronic devices.