Hydrogen-terminated Polycrystalline Diamond Research Articles

Photoelectric characteristics of hydrogen-terminated polycrystalline diamond MESFETs.

In the field of diamond MESFETs, this work is what we believe to be the first to investigate the optoelectronic properties of hydrogen-terminated polycrystalline diamond MESFETs under visible and near-UV light irradiation. It is shown that the diamond MESFETs are well suited for weak light detection in the near-ultraviolet region around the wavelength of 368 nm, with a responsivity of 6.14 × 106 A/W and an external quantum efficiency of 2.1 × 107 when the incident light power at 368.7 nm is only 0.75 µW/cm2. For incident light at 275.1 nm, the device's sensitivity and EQE increase as the incident light power increases; at an incident light power of 175.32 µW/cm2 and a VGS of -1 V, the device's sensitivity is 2.9 × 105 A/W and the EQE is 1.3 × 106. For incident light in the wavelength range of 660 nm to 404 nm with an optical power of 70 µW/cm2, the device achieves an average responsivity of 1.21 × 105 A/W. This indicates that hydrogen-terminated polycrystalline diamond MESFETs are suitable for visible and near-UV light detection, especially for weak near-UV light detection. However, the transient response test of the device shows a long relaxation time of about 0.2 s, so it is not yet suitable for high-speed UV communication or detection.

The influence of hydrogen plasma etching on the surface conductivity of the polycrystalline diamond surface and the temperature-dependent properties

With the development of carbon-based electronics, the polycrystalline diamond has drawn much attention in diamond electronic devices; as compared to single crystalline diamond, the scale of the polycrystalline diamond can be fabricated over 4 in. much more easily. However, until now, the influence factors on the surface conductivity of hydrogen-terminated polycrystalline diamond (H-PCD) are still unclear. In this work, the carrier concentration and mobility of H-PCD were investigated through Hall effect measurement. It was found that besides surface roughness, the temperature at which the equilibrium states of adsorption and desorption of H-PCD surface adsorbates are established also plays an important role in carrier concentration and mobility. With the increase of the establishment temperature, both carrier concentration and mobility show a decreasing tendency, which may be determined by the coefficient of the surface ionic scattering, phonon scattering, and the grain boundaries on the H-PCD surface. The investigation of this work will give some insight into the control of the surface conductivity on H-PCD from the aspect of the equilibrium state established temperature and surface roughness.

650 mW/mm output power density of H‐terminated polycrystalline diamond MISFET at 10 GHz

In this work, metal–insulator–semiconductor field effect transistors (MISFET) with gate length of 350 nm were fabricated on hydrogen-terminated polycrystalline diamond by a self-aligned process. Aluminium film with thickness of 2 nm was evaporated on the sample and formed self-oxidised alumina to act as the gate dielectric. The devices show good direct current and radio frequency performances with a maximum frequency of oscillation (f max) of 34 GHz and continuous-wave output power density of 650 mW/mm at 10 GHz.

Hydrogen-terminated polycrystalline diamond MOSFETs with Al2O3 passivation layers grown by atomic layer deposition at different temperatures

Metal oxide semiconductor field effect transistors (MOSFETs) with Al2O3 passivation layer grown by atomic layer deposition (ALD) at 200 oC and 300 oC were fabricated on hydrogen-terminated polycrystalline diamond by using gold mask technology. The device with 200 oC grown Al2O3 dielectric shows high output current, low on-resistance, large threshold voltage and high transconductance compared to that with 300 oC grown Al2O3. A maximum drain current of 339 mA/mm has been achieved by the 2-μm device of the former kind, which, as we know, is the best result reported for the diamond MOSFETs with the same gate length except the NO2-adsorbed case. The current-voltage (I-V) of gate diodes of both kinds of devices show the gate forward leakage is dominated by the Frenkel-Poole (FP) emission mechanism at a high electric field, and the gate of the latter device can sustain higher forward bias. The stability of successive I-V measurements of both kinds of devices was proved. We expect that a high performance H-diamond MOSFET with high stability can be achieved by a double-layer dielectric structure with 200 oC grown Al2O3 stacked by another high-quality high κ dielectric.

Polycrystalline Diamond MOSFET With MoO3 Gate Dielectric and Passivation Layer

We report the hydrogen terminated polycrystalline diamond MOSFET with a 10-nm MoO3 gate dielectric and a 50-nm MoO3 passivation layer. The device with a gate length of $2~\mu \text{m}$ shows the saturation drain current ( ${I}_{Dsat})$ of 100mA/mm, the transconductance of 35 mS/mm, and the ON-resistance of $76.54~\Omega \cdot $ mm at ${V}_{GS} = -2.5$ V. The stability of the repeated ${I}_{DS} $ – $ {V}_{GS}$ measurements was demonstrated by a mere ${I}_{Dsat}$ decrease of 3.3% between the first and third sweepings. In addition, the devices worked well at 200 °C delivering even larger ${I}_{Dsat}$ than that at room temperature. The possible mechanisms for ${I}_{DS}$ – $ {V}_{GS}$ changes in the successive measurements and induced by the change of the ambient temperature are suggested.

DC and RF performance of surface channel MESFETs on H-terminated polycrystalline diamond

DC and RF performance of submicron gate-length metal–semiconductor field effect transistors (MESFETs) fabricated on hydrogen-terminated polycrystalline diamond is investigated in detail for different material electronic quality (grain size in the range 100–200 µm) and device geometry (drain-source channel length in the range 1–3 µm). DC characteristics appear almost independent of both properties, giving maximum drain-source current values in the range 120–140 mA/mm in MESFETs having same gate length (0.2 µm) and gate width (25 µm). The layer properties underneath the hydrogenated surface seem then to affect the DC behaviour to a lesser extent when the same hydrogenation procedure is used. At variance, the electronic quality of diamond layers employed for MESFETs realization largely affects the RF performance, resulting into a low oscillation frequency f max for a MESFET realized by a self-aligned process (1 µm drain-source channel length) onto low quality diamond polycrystalline film. Such a performance improves to f max = 35 GHz for devices realized onto large grain polycrystalline diamond, although fabricated without self-aligned gate procedure (3 µm drain-source channel length). These findings are discussed in terms of different roles played by surface hydrogenation, device geometry detail and electronic quality of the polycrystalline diamond substrate for MESFET realization.

Inhomogeneous DNA bonding to polycrystalline CVD diamond

Double stranded deoxyribonucleic acid (ds-DNA) layers, bonded to hydrogen terminated polycrystalline diamond, are characterized by scanning electron (SEM), fluorescence (FM), and atomic force microscopy (AFM). DNA grafting has been achieved using photochemical bonding of ω-unsaturated 10-amino-dec-1-ene molecules. SEM detects local variations of electron affinities on polycrystalline diamond, revealing distinct grain structures. FM applied on fluorescence labeled ds-DNA show laterally varying intensities of typically 20%, which resembles also grain structure as detected by SEM. Contact and tapping-mode AFM characterization reveal a tilted DNA bonding to diamond and a dense layer formation which gives rise to smoothening of surface properties. The lateral density variation of DNA is attributed to local variations of the photo-electron emission efficiency which affects the photochemical attachment chemistry of amine-linker molecules to diamond.

DNA Bonding to CVD Diamond Probed by Scanning Electron-, Fluorescence-, and Atomic force- Microscopy

ABSTRACTDouble stranded desoxyribonucleic acid (ds-DNA) layers, bonded to hydrogen terminated polycrystalline diamond, are characterized by scanning electron (SEM), fluorescence (FM), and atomic force microscopy (AFM). DNA grafting has been achieved using photochemical bonding of ω-unsaturated 10-amino-dec-1-ene molecules. SEM detects local variations of electron affinities on polycrystalline diamond, revealing distinct grain structures. FM applied on fluorescence labeled ds-DNA show laterally varying intensities of typically 20 %, which resembles also grain structure as detected by SEM. Contact and tapping mode AFM characterization reveal a tilted DNA bonding to diamond, dense layer formation which gives rise to smoothening of surface properties. The lateral density variation of DNA is attributed to local variations of the photo-electron emission efficiency which affects the photochemical attachment chemistry of amine linker molecules to diamond.

Interaction of thermally activated and molecular oxygen with hydrogenated polycrystalline diamond surfaces studied by synchrotron radiation techniques

In the present work we study the interactions between thermally activated and molecular (unactivated) oxygen gas with a hydrogen-terminated polycrystalline diamond film surface. As revealed by H + photodesorption measurements using excitation energies in carbon and oxygen K-edges, and X-ray photoelectron spectroscopy, molecular oxygen does not adsorb onto the hydrogenated diamond surface. However, thermally activated oxygen does adsorb onto it. A dominant reaction path leads to the formation of surface C–O–H bonds, although it is likely that some abstraction of chemisorbed hydrogen with formation of carbonyl bonds happens as well. The effect of oxygen on the electron emission properties of the films is studied by photon induced secondary electron emission (SEE) spectroscopy. The hydrogen-terminated, oxygen-free diamond surface exhibits negative electron affinity and high SEE intensity. Adsorption of thermally activated oxygen results in a slightly positive electron affinity (∼0.4 eV) and a decrease in the intensity of SEE, whereas electron emission properties of this sample following exposure to molecular oxygen seem to be unaffected.

Effect of average grain size on the work function of diamond films

The work function of hydrogen-terminated polycrystalline diamond films deposited by electrophoresis on molybdenum was studied using ultraviolet photoelectron spectroscopy with 21.2 eV photons for average grain sizes ranging from 0.32 to 108 μm. The work function has a maximum of about 5.1 eV at 0.32 μm, then decreases with increasing grain size to a minimum of about 3.2 eV at an average grain size of about 4 μm and then increases to a value of about 4.8 eV at a grain size of 108 μm. The results are consistent with a model in which the work function is controlled by the work function of single crystal diamond (111) at the larger grain sizes, graphitic carbon at the smaller grain sizes, and by a negative electron affinity that increases with decreasing grain size due to defects near diamond (111) crystallite edges for the intervening grain sizes. The large change in work function (almost a factor of 2) could be useful to make conductors with different work functions for microelectronic gate structures.

Small signal equivalent circuit of an isotype heterojunction dominated by traps : M. J. Hampshire and R. D. Tomlinson, Solid-St. Electron. 13 (1970), p. 41

DC and RF performance of submicron gate-length metal–semiconductor field effect transistors (MESFETs) fabricated on hydrogen-terminated polycrystalline diamond is investigated in detail for different material electronic quality (grain size in the range 100–200 µm) and device geometry (drain-source channel length in the range 1–3 µm). DC characteristics appear almost independent of both properties, giving maximum drain-source current values in the range 120–140 mA/mm in MESFETs having same gate length (0.2 µm) and gate width (25 µm). The layer properties underneath the hydrogenated surface seem then to affect the DC behaviour to a lesser extent when the same hydrogenation procedure is used. At variance, the electronic quality of diamond layers employed for MESFETs realization largely affects the RF performance, resulting into a low oscillation frequency fmax for a MESFET realized by a self-aligned process (1 µm drain-source channel length) onto low quality diamond polycrystalline film. Such a performance improves to fmax = 35 GHz for devices realized onto large grain polycrystalline diamond, although fabricated without self-aligned gate procedure (3 µm drain-source channel length). These findings are discussed in terms of different roles played by surface hydrogenation, device geometry detail and electronic quality of the polycrystalline diamond substrate for MESFET realization.