Diamond Metal-semiconductor Field-effect Transistor Research Articles

Radiation effect of X-ray with 100 kGy dose on the electrical properties of MESFET based on hydrogen-terminated diamond surface conductivity

The irradiation effect of X-ray on the electrical properties of Schottky-barrier diode (SBD) and metal-semiconductor field-effect transistors (MESFET) based on the surface conductivity of hydrogen-terminated single-crystal diamond (SCD) epilayers was investigated. The Ohmic contact was formed by a Pd/Ti/Au multilayer and the Schottky metal was Al thin film for the fabrication of the diamond SBDs and MESFETs. The X-ray irradiation was performed with a dose of 100 kGy. It was observed that both the forward current of the SBDs and the drain current of the MESFETs experienced a reduction after the X-ray irradiation. The type of the single-crystal diamond substrate had an obvious effect on the radiation properties. For the MESFETs on the type-Ib SCD substrate, the variation of the drain currents as the irradiation was inhomogeneous across the devices. For the MESFETs on the type-IIa SCD substrate, the reduction of the drain currents is more uniform and the threshold voltage changed little upon X-ray irradiation. The partial oxidation in the air of the exposure area in the device and the edge of the Al gate may be responsible for the degradation of the device performance under X-ray irradiation. The passivation technique with radiation-robustness is needed for diamond devices based on the surface conductivity of diamond.

N-Type Diamond Metal-Semiconductor Field-Effect Transistor With High Operation Temperature of 300°C

The development of diamond power devices has been hindered due to the challenge in the achievement of n-type diamond electronic devices. In this study, we report the phosphorus-doped n-type diamond metal-semiconductor field-effect transistor (MESFET). We selectively grew heavily phosphorus doped diamond layer to improve the ohmicity of the source and drain contacts. The MESFET showed clear pinch-off and saturation characteristics. The transconductance was improved to be 0.1 <inline-formula> <tex-math notation="LaTeX">$\mu \text{S}$ </tex-math></inline-formula>/mm by 100 times from room temperature to 300&#x00B0;C.

Polycrystalline diamond normally-off MESFET passivated by a MoO3 layer

The normally-off hydrogen-terminated diamond metal–semiconductor field effect transistors (MESFETs) with a MoO3 passivation layer were fabricated on the CVD grown polycrystalline diamond substrate. The characteristics of the device at room temperature and 100 °C, 150 °C and 200 °C were investigated. The device with a 2-μm gate shows a threshold voltage of −0.38 V, the maximum output current of 35 mA/mm and the transconductance of 17.4 mS/mm. The device can still work normally until 150 °C, which shows great potential to be used in high temperature in the future.

Cause and Effects of OFF-State Degradation in Hydrogen-Terminated Diamond MESFETs

This article reports the first comprehensive analysis of the reliability of hydrogen-terminated diamond metal semiconductor field-effect transistors (MESFETs) submitted to OFF-state stress. We demonstrate that stress induces an increase in ON-resistance and a shift in the threshold voltage, along with a decrease in the transconductance peak value. These effects are ascribed to the generation of defects at the diamond surface and/or in the upper semiconductor layers. The defects are generated both in the access regions and under the gate, and their activation energy is 0.30 eV.

Improved drain current of diamond metal–semiconductor field-effect transistor by selectively grown p+ contact layer

Diamond metal–semiconductor FETs are attractive for high-temperature, high-radiation proof electronics. However, in the lateral-channel structure, source/drain contacts directly deposited on the drift layer induce a high series resistance. To maximize the drain current, herein a heavily-boron-doped (p+) contact layer was introduced underneath the source/drain contacts by selective-area growth. The RT drain current density was effectively increased from 0.06 to 0.2 mA mm−1. Moreover, the contact resistance between the selectively grown p+ layer and the drift layer was evaluated by the transmission line model.

Electric Field Characterization of Diamond Metal Semiconductor Field Effect Transistors Using Electron Beam Induced Current

Lateral gate depletion expansion towards drain contact has been analyzed on p-type diamond metal-semiconductor field effect transistor by electron beam induced current. The investigation was restricted to a closed channel to simplify the study and to directly observe the expansion of the lateral depletion region. The experimental data agreed with the theoretical model given in the literature.

Diamond Metal–Semiconductor Field-Effect Transistor With Breakdown Voltage Over 1.5 kV

A diamond metal-semiconductor field-effect transistor (MESFET) with a Pt Schottky gate was fabricated. The MESFET exhibited clear saturation and pinchoff characteristics. The drain current of the MESFET operated at 300 °C was 20 times higher than that at room temperature due to the activation of acceptors. The breakdown voltage was highly dependent on the gate-drain length and reached 1.5 kV at a gate-drain length of 30 μm, which is the highest reported for a diamond FET.

Polycrystalline diamond MESFETs by Au-mask technology for RF applications

Metal-semiconductor field effect transistors (MESFETs) were fabricated on H-terminated polycrystalline diamond. The DC characteristics of the p-channel MESFET showed a maximum drain current density of 204 mA/mm at a gate-source voltage of −6 V, and a maximum transconductance of 20 mS/mm at a drain-source voltage of −1.5 V. The small signal S-parameters of MESFET with 2 × 100 μm gate width and 2 μm gate length were measured. An extrinsic cut-off frequency (fT) of 1.7 GHz and the maximum oscillation frequency (fmax) of 2.5 GHz were obtained, which was the first report on diamond MESFETs with RF characteristics in China.

Diamond MESFET performance improvement by layout optimisation

Hydrogen terminated diamond is a promising material for metal semi-conductor field effect transistor (MESFETs) fabrication and research effort is focused on diamond quality improvement. In this reported work, the focus of attention is on device layout and structure to improve RF performances, designed on the basis of diamond physical properties, taking into account the characterisation of previously fabricated devices. Significant increase of current gain cutoff frequency fT, from 3.4 to 6.7 GHz, has been obtained, while maximum oscillation frequency fMAX is raised from 10.4 to 11.8 GHz.

RF Performance of Diamond Metel–Semiconductor Field-Effect Transistor at Elevated Temperatures and Analysis of its Equivalent Circuit

Temperature dependent DC and RF characteristics of p-type diamond metal–semiconductor field-effect transistors (MESFETs) on hydrogen-terminated surfaces are investigated. The device is thermally stable up to 100 °C, because it does not deteriorate at all at higher temperatures. Temperature coefficients of transconductance (gm), drain conductance (gds), gate–source capacitance (Cgs), gate–drain capacitance (Cgd), cut-off frequency ( fT), and maximum drain current (Ids) were obtained from small-signal equivalent circuit analysis. The cut-off frequency ( fT) is almost totally independent of temperature. Intrinsic gm, gds, and Cgs decrease with increasing temperature. Cgd is almost totally independent of temperature. The threshold voltage shifts to the negative side with increasing temperature. We propose a band model of an Al-gate contact/H-terminated diamond to explain the temperature dependence of these components.

Temperature dependent DC and RF performance of diamond MESFET

This paper reports the first studies on temperature dependent DC and RF characteristics of diamond metal-semiconductor field-effect transistors along with circular-transmission-line-method measurements on hydrogen-terminated diamond surface. In general, the device under study is thermally stable up to 100 °C as it does not deteriorate at higher temperatures with the cut-off frequency for current gain maintained at 8∼9 GHz. It is found that the sheet resistance is almost totally independent of temperature, contact resistance is negligible, and channel conductance underneath the gate decreases with increasing temperature. The threshold voltage for the device is found to shift to the negative side with increasing temperature. A small-signal equivalent circuit analysis reveals that both transconductance and gate-source capacitance decrease with increasing temperature, which results in the almost constant cut-off frequency for current gain. The experimental results can be explained by the fact that with increasing temperature, the band near the Al/H-terminated diamond surface bends upward more weakly, which leads to a decrease of buffer capacitance. At the same time the mobility decreases and the transconductance therefore decreases.

Microwave Performance of Diamond Field-Effect Transistors

The microwave performance of diamond metal semiconductor field-effect transistors (MESFET) and metal insulator semiconductor field-effect transistors (MISFET) fabricated on hydrogen-terminated diamond surface is investigated. A cut-off frequency of 2.2 GHz is obtained on a 2 µm Cu gate MESFET with a transconductance of 70 mS/mm. A cut-off frequency of 11 GHz is obtained on a 0.7 µm gate MISFET with a transconductance of 40 mS/mm. Despite the lower transconductance, the cut-off frequency of MISFET is higher than that of MESFET due to not only gate minimization but also increased carrier mobility due to the use of CaF2 as the gate insulator. High-frequency equivalent circuits are derived from S-parameters for MISFET with various gate lengths. Reduction of gate-source parasitic resistance and capacitance in MISFET by the improvement of device structure yield high frequency performance.

High-frequency performance of diamond field-effect transistor

The microwave performance of a diamond metal-semiconductor field-effect transistor (MESFET) is reported for the first time. MESFETs with a gate length of 2-3 /spl mu/m and a source-gate spacing of 0.1 /spl mu/m were fabricated on the hydrogen-terminated surface of an undoped diamond film grown by microwave plasma chemical vapor deposition (CVD) utilizing a self-aligned gate fabrication process. A maximum transconductance of 70 mS/mm was obtained on a 2 /spl mu/m gate MESFET at V/sub GS/=-1.5 V and V/sub DS/=-5 V,for which a cutoff frequency f/sub T/ and a maximum oscillating frequency f/sub max/ of 2.2 GHz and 7 GHz were obtained, respectively.

Characterization of Diamond Surface-Channel Metal-Semiconductor Field-Effect Transistor with Device Simulation

The DC operation of surface-channel metal-semiconductor field-effect transistors (MESFETs) using p-type conductive layers on hydrogen-terminated diamond surfaces is investigated by two-dimensional device simulation. As a result, a model to describe the surface semiconducting layer, in which acceptors are distributed two-dimensionally on the surface, is found to reproduce actual device characteristics well. Based on the model, the carrier (hole) concentration at a depth of 10 nm is determined to be three orders less than that at the surface. This thin channel realizes complete channel pinch-off and drain-current saturation with high transconductance, observed in the actual diamond surface-channel MESFETs. In the simulation, the transconductance of diamond surface-channel MESFETs with a self-aligned 1 µm gate exceeds 100 mS/mm. This result agrees well with a recent experimental result. The transconductance over 100 mS/mm can compete with that of Si metal-oxide-semiconductor field-effect transistors (MOSFETs) of the same gate length. The hydrogen-terminated diaomond surface is naturally equipped with the silicon-on-insulator-like (SOI-like) thin channel and shallow junction depth required for a nanoscale FET, such as one with a gate length of less than 50 nm.

High-temperature, high-voltage operation of pulse-doped diamond MESFET

The fabrication and operation of a pulse-doped diamond metal-semiconductor field-effect transistor (MESFET) is presented showing a usable source drain voltage of 70 V and no breakdown up to 100 V at 350/spl deg/C operating temperature. A channel sheet concentration of 8.5×10/sup 12/ cm/sup -2/ could be fully modulated leading to a maximum transconductance of 0.22 mS/mm, although full activation of the boron acceptor had not been reached. For an optimized device structure, with reduced gate length below 0.25 μm and full activation, more than 10 W/mm RF-power density can be predicted.

Pulse-doped diamond p-channel metal semiconductor field-effect transistor

A p-type diamond metal semiconductor field-effect transistor (MESFET) structure, utilizing a boron pulse-doped layer as the conducting channel, has been successfully fabricated. The pulse-doped structure consists of an undoped diamond buffer layer, a highly doped thin diamond active layer, and an undoped diamond cap layer grown by the microwave plasma assisted chemical vapor deposition method. It is shown that this field-effect transistor with a gate length of 4 μm and the gate width of 39 μm exhibits an extrinsic transconductance of 116 μS/mm with both pinch-off characteristics and current saturation.

Diamond devices made of epitaxial diamond films

In order to improve the characteristics of diamond metal semiconductor field-effect transistors (MESFETs), a new structure having a non-doped layer between the gate electrode and the boron-doped layer was fabricated using selective epitaxial growth. The gate electrode was made of aluminum and the source and drain electrodes were made of tungsten. This FET was found to have a tendency toward drain current saturation at room temperature and to operate at 300°C.

The potential of diamond and SiC electronic devices for microwave and millimeter-wave power applications

The potential of SiC and diamond for producing microwave and millimeter-wave electronic devices is reviewed. It is shown that both of these materials possess characteristics that may permit RF electronic devices with performance similar to or greater than what is available from devices fabricated from the commonly used semiconductors, Si, GaAs, and InP. Theoretical calculations of the RF performance potential of several candidate high-frequency device structures are presented: the metal semiconductor field-effect transistor (MESFET), the impact avalanche transit-time (IMPATT) diode, and the bipolar junction transistor (BJT). Diamond MESFETs are capable of producing over 200 W of X-band power as compared to about 8 W for GaAs MESFETs. Devices fabricated from SiC should perform between these limits. Diamond and SiC IMPATT diodes also are capable of producing improved RF power compared to Si, GaAs, and InP devices at microwave frequencies. RF performance degrades with frequency and only marginal improvements are indicated at millimeter-wave frequencies. Bipolar transistors fabricated from wide bandgap material probably offer improved RF performance only at UHF and low microwave frequencies. >