Characteristics Of H-diamond MOSFET With High Temperature ALD-grown HfO₂ Dielectric

Diamond has great potential for applications in the field of high-voltage,high-frequency and high-power electronic devices due to its outstanding properties,such as wide band gap,high thermal conductivity and high carrier mobility.The two-dimensional hole gas(2DHG)induced at the hydrogen-terminated diamond(H-diamond)surface provides a conductive channel for H-diamond devices,which greatly promotes the development and application of diamond devices.However,the H-diamond surface conductivity is very sensitive to the temperature.Desorption of acceptor-like adsorbates on the surface easily occur due to high-temperature process,then the surface conductivity degraded severely and affected the electrical characteristics of the device.It has been reported that most of the H-diamond metal-oxide-semiconductor field effect transistors(MOSFET)with high breakdown voltage use 200-400 nm thick oxide film as the gate dielectric layer or passivation layer.However,the very thick dielectric layer weakens the gate control on the channel.In view of the research background mentioned above,this paper studied the dielectric/H-diamond interface characteristics,and then fabricated and tested high-performance hydrogen-terminated diamond MOSFET devices.The specific research work and results are as follows.1.The effect of annealing temperature on the ohmic contact and hole conductivity of the unpassivated H-diamond surface are investigated.It is found that the sheet resistance of the H-diamond surface increased gradually with increasing annealing temperature from 5.8k?/?at room temperature to 17 k?/?after being annealed at 600?.However,the ohmic contact resistivity decreased steadily from 9.34×10^-4?·cm²at room temperature to4×10^-7?·cm²after 600?annealing.2.The interfacial band configuration between ALD-Hf O₂grown at 300?and H-diamond was investigated by using X-ray photoelectron spectroscopy.It is found out that band gap of Hf O₂is 5.16 e V,and the conduction band offset and the valence band shift at the Hf O₂/H-diamond interface are 2.31 e V and 2.00 e V,respectively.The staggered energy band structure shows that ALD-Hf O₂has great potential to accommodate high density of holes and it is suitable for p-channel H-diamond MOSFET.3.The ALD-Hf O₂/H-diamond MOSFETs with different gate lengths were fabricated on polycrystalline diamond substrates.The transistors exhibit high on/off ratio,which is close to 10⁹,indicating that the ALD-Hf O₂layer grown at 300?can effectively suppress gate leakage.The high-voltage ALD-Hf O₂/H-diamond MOSFET with different gate-to-drain distances are also fabricated.The device with gate length of 2?m and gate-to-drain distance of 30?m exhibits the maximum output current compared with the reported H-diamond devices of the same size under the same test conditions.At the same time,it maintains high on/off ratio and low subthreshold swing.The high-voltage test shows that the Baliga figure of merit is about 2.0MW/cm²,which rivals that of the H-diamond MOSFET with the record high breakdown voltage of 2000V.In conclusion,high-temperature(300?)ALD-Hf O₂was used as a dielectric layer to prepare high-voltage H-diamond MOSFETs at the first time.The device exhibits a high on/off ratio and desirable gate control capability.At the same time,the Baliga figure of merit rivals that of the H-diamond MOSFET with the record high breakdown voltage of2000V.The above experiments have confirmed that ALD-Hf O₂is suitable for high-voltage H-diamond MOSFETs.