We fabricated inversion channel diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with normally off characteristics. At present, Si MOSFETs and insulated gate bipolar transistors (IGBTs) with inversion channels are widely used because of their high controllability of electric power and high tolerance. Although a diamond semiconductor is considered to be a material with a strong potential for application in next-generation power devices, diamond MOSFETs with an inversion channel have not yet been reported. We precisely controlled the MOS interface for diamond by wet annealing and fabricated p-channel and planar-type MOSFETs with phosphorus-doped n-type body on diamond (111) substrate. The gate oxide of Al2O3 was deposited onto the n-type diamond body by atomic layer deposition at 300 °C. The drain current was controlled by the negative gate voltage, indicating that an inversion channel with a p-type character was formed at a high-quality n-type diamond body/Al2O3 interface. The maximum drain current density and the field-effect mobility of a diamond MOSFET with a gate electrode length of 5 μm were 1.6 mA/mm and 8.0 cm2/Vs, respectively, at room temperature.

We demonstrate high-efficiency excitonic emission with deep-ultraviolet (DUV) light of 235 nm at room temperature for a (111)-oriented diamond p-i-n junction light-emitting diode (LED) by introducing a thick i-layer. Significant enhancement in excitonic emission efficiency of over 500 times was observed for a diamond LED by increasing the i-layer thickness from 0.1 to 14 μm. Maximum output power and external quantum efficiency of excitonic emission for the LED without any specific device structure were 0.1 mW and 0.006%, respectively, under pulsed-current injection. We also demonstrate the sterilization of Escherichia coli by irradiation with DUV light from the diamond LED.

Diamond diodes with extremely low on-resistance are introduced and discussed. Heavily boron-doped p + -type and phosphorus-doped n + -type diamond films with hopping conduction at room temperature are utilized. These diamond films have a unique property, that is, their resistivity decreases drastically even at a high impurity concentration of >10 20 cm %3 without degrading the crystallinity. This unique property is applied to two kinds of diamond diodes. One is a p + -i-n + junction diode. The other is a Schottky-pn diode consisting of the combination of the p + -n and n-type Schottky junctions. Current-voltage and capacitance-voltage characteristics are evaluated for both diodes. Switching characteristics are also evaluated for Schottky-pn diodes. The results show a low on-resistance on the order of mΩ cm 2 and fast switching on the ns order. These results indicate that the low-loss diamond diodes can be realized by using the hopping p + -and n + -type layers.

We fabricated a diamond diode, namely a Schottky-pn diode (SPND), which is composed of a fully depleted n-type active layer sandwiched between a highly doped p-type layer and a Schottky metal layer. The SPND has superior characteristics that overcome the weak points of both a Schottky barrier diode and a pn diode. That is, the SPND showed high current density (over 4000 A/cm2) with low specific resistance (0.4 mΩ cm2) at a forward bias of 6 V while maintaining a high rectification ratio of ∼1010. Moreover, the SPND showed extremely fast turn-off speed of nanosecond order.

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We successfully observed electron emission from hydrogenated diamond (111) p–i–n+ junction diodes with negative electron affinity during room temperature operation. A heavily doped layer and p–i–n junction structure, rather than a p–n junction structure, play important roles in obtaining high diode and emission currents. The emission started when the applied bias voltage was equal to the expected built-in potential, and the emission current reached 8.8 µA during the room temperature operation. In this high current region, we observed an increase in quantum efficiency – a nonlinear increase in emission current.

HighlightsWe evaluated the genotoxicity of styrene oligomers extracted from polystyrene intended for use in contact with food.Compared with 50% ethanol, acetone extracted a far greater amount of styrene dimers and trimers from polystyrene.Ames tests and an in vitro chromosomal aberration test were negative.The risk of the genotoxicity of styrene oligomers migrated from polystyrene food packaging into food is likely very low.

We successfully fabricated a diamond diode, namely a Schottky p–n diode (SPND), which is composed of a fully depleted n‐type active layer sandwiched between a highly doped p‐type layer and a Schottky metal. The diamond SPND showed a high forward current density (over 4000 A cm−2 at 6 V) with a low built‐in voltage (∼1.5 V) at room temperature while maintaining a high rectification ratio of ∼1010. Further improvement of the high forward current density characteristics was found at high temperature. The SPND can be realized with higher forward current density than that of conventional diamond Schottky barrier diode, p–n diode, and recently proposed merged diodes, while maintaining the high rectification ratio.