We report the 250 degrees C operation of a diamond-based monolithic bidirectional switch. A normally-ON double gate deep depletion MOSFET was fabricated with a 400 nm p-type channel with a boron doping of [N-A-N-D] = 2.3 x 10(17) cm(-3) and an Al2O3 gate oxide thickness of 50 nm. The Ist and IIIrd quadrants transistor characteristics are successfully measured by controlling the channel conductivity with both gates separately, with a clear ON and OFF state. A threshold voltage around 35 V is obtained with a low minimum gate leakage current of 1.00 x 10(-4) mA/mm at a gate-source bias V-GS = 50 V. The bidirectional switch is then obtained by operating the MOSFET in the Ist quadrant of each gate setup. This first proof of concept offers a reverse conducting and reverse blocking diamond MOSFET, with only one drift region layer.

This paper proposes a system-level comparison between diamond and silicon carbide (SiC) power devices. It highlights the benefits of diamond semiconductors for power electronics applications. Actual diamond power devices were fabricated and characterised (DC, AC small-signal, large-signal power switching in a buck converter). Models of the diamond devices are discussed based on the experimental data, and the expected performances of the future diamond semiconductors in power converters are presented. These performances are compared to the commercialised SiC Schottky diodes for a given application. Our analysis shows that diamond devices can be used to increase the performance of power converters, especially at high temperatures. We demonstrate that for a junction temperature of 450 K, diamond semiconductors can divide the semiconductor losses and heatsink volume by three, in comparison with SiC devices. We also demonstrate that the switching frequency with diamond devices can be five times higher than with SiC devices, with lower total semiconductor losses and smaller heatsink in diamond-based power converters. This system-level analysis clearly shows the future improvements in the efficiency and power densities of power converters thanks to diamond power devices. The need for management of the specific junction temperature, which is required in order to exploit all of the properties of diamonds, is demonstrated and discussed.

Owing to its outstanding electro-thermal properties, such as the highest thermal conductivity (22 W/(cm∙K) at room temperature), high hole mobility (2000 cm2/(V∙s)), high critical electric field (10 MV/cm) and large band gap (5.5 eV), diamond represents the ultimate semiconductor for high power and high temperature power applications. Diamond Schottky barrier diodes are good candidates for short-term implementation in power converters due to their relative maturity. Nonetheless, diamond as a semiconductor for power devices leads to specificities such as incomplete dopant ionization at room temperature and above, and the limited availability of implantation techniques. This article presents such specificities and their impacts on the optimal design of diamond Schottky barrier diodes. First, the tradeoff between ON-state and OFF-state is discussed based on 1D analytical models. Then, 2D numerical studies show the optimal design of floating metal rings to improve the effective breakdown voltage. Both analyses show that the doping of the drift region must be reduced to reduce leakage currents and to increase edge termination efficiency, leading to better figures of merit. The obtained improvements in breakdown voltage are compared with fabrication challenges and the impacts on forward voltage drop.

In this paper, we introduce a set of experiments and analyses to comprehensively correlate the epitaxial structural defects and electrical characteristics in the pseudovertical homoepitaxial boron-doped oxygen-terminated (001) diamond metal-oxide-semiconductor capacitors (MOSCAPs). Current-voltage I(V), capacitance-voltage C(V), and capacitance-frequency C(f) characteristics of the MOSCAPs have been measured and analyzed, with the special focus when the structure is under positive bias, i.e., depletion regime. The defective spots, which are electrically active, have been identified as the origin of the MOSCAP's leakage current in depletion regime. The electrical features of these killer defects are characterized thanks to micrometer scale electrical measurements equipped under scanning electron microscope. The structural features of these killer defects are explored by transmission electron microscopy. By taking into account, the electrical characteristics of the killer defects, we introduced and simulated a small signal equivalent circuit of the whole structure. The comparison between simulations with ac measurements confirms that the gate leakage current appearing in depletion regime induces an inversionlike artifact observed on diamond MOSCAPs C(f, V).

This paper presents the integration of diamond Schotkky barrier diodes (SBDs) for power electronics applications and the problematics linked to their implementation in power converters. Various approches are considered for increasing the current rating of the power device. In particular, the parallelization and the interleaving of pseudo-vertical diamond SBDs are investigated. This study allows to evidence interactions between diodes from the same die which can result in unbalanced current distribution between diodes with differences in electrical performances. Modifications of the device structure are proposed in order to overcome this issue for improving the implementation of future diamond devices in power electronics applications.

Metal oxide semiconductor capacitors were fabricated using p-type oxygen-terminated (001) diamond and Al2O3 deposited by atomic layer deposition at two different temperatures 250 °C and 380 °C. Current voltage I(V), capacitance voltage C(V), and capacitance frequency C(f) measurements were performed and analyzed for frequencies ranging from 1 Hz to 1 MHz and temperatures from 160 K to 360 K. A complete model for the Metal-Oxide-Semiconductor Capacitors electrostatics, leakage current mechanisms through the oxide into the semiconductor and small a.c. signal equivalent circuit of the device is proposed and discussed. Interface states densities are then evaluated in the range of 1012eV−1cm−2. The strong Fermi level pinning is demonstrated to be induced by the combined effects of the leakage current through the oxide and the presence of diamond/oxide interface states.

The interfacial band configuration of the high-κ dielectric Al2O3 deposited at 120 ∘C by atomic layer deposition (ALD) on boron- and phosphorus-doped hydrogen-terminated (111) diamond was investigated. Performing X-ray photoelectron spectroscopy measurements of core level binding energies and valence band maxima values, the valence band offsets of both heterojunctions are found to be ΔEV = 1.8 eV and ΔEV = 2.7 eV for Al2O3/H(111)p and Al2O3/H(111)n, respectively. The ALD Al2O3 bandgap energy was measured from the O 1s photoelectron energy loss spectra to be EGAl2O3=7.1 eV. The interfacial band diagram configuration is found to be of type II for both Al2O3/H(111)p and Al2O3/H(111)n heterostructures having conduction band offsets of ΔEC = 0.2 eV and ΔEC = 1.1 eV, respectively. The use of doped (111) hydrogen-terminated diamond for developing future diamond metal-oxide-semiconductor field-effect transistors is discussed.

Cet article presente les avancees sur la simulation analytique et numerique de composants de puissance en diamant, ainsi que les problematiques de caracterisation associees. Les modeles specifiques au diamant ont ete implementes et ont ete calibres en confrontant les resultats de simulation aux dernieres donnees experimentales existantes. Enfin, un soin particulier a ete apporte sur la maitrise de l'auto-echauffement et de la calibration de la temperature du composant diamant sous test.

Heterostructures such as Schottky diodes and metal/oxide/semiconductor structures are the building blocks of diamond electronic devices. They are able to carry large current densities, up to several kA cm(-2), if a heavily boron-doped layer (p(++)) is included in the semiconducting stack, thus affording a metallic reservoir of mobile holes close to the lightly doped layer (p(-)). In this work, hole injection effects are evidenced experimentally in the two previously mentioned devices and also simulated numerically. Although the potential barrier height at metal/semiconductor interfaces is a fundamental parameter, a more general approach consists in defining the current density from the product of an effective velocity and carrier concentration at interface. In accordance with experimental results, such a view permits to describe both depletion and accumulation regimes, which indeed can exist at the metallic or oxide interface, and to take into account the increase of the hole concentration above the thermal equilibrium one in the p-layer. The lower the temperature, the larger is this second effect. For sufficiently thin p-layers, typically below 2 mu m, this effect frees device operation from the limitation due to incomplete ionization of acceptors and allows a strong decrease of the specific resistance and forward losses while preserving breakdown voltages in the range of 1.4-2 kV. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Electrical properties of metal-semiconductor (M/SC) and metal/oxide/SC structures built with Zr or ZrO2 deposited on oxygen-terminated surfaces of (001)-oriented diamond films, comprised of a stack of lightly p-doped diamond on a heavily doped layer itself homoepitaxially grown on an Ib substrate, are investigated experimentally and compared to different models. In Schottky barrier diodes, the interfacial oxide layer evidenced by high resolution transmission electron microscopy and electron energy losses spectroscopy before and after annealing, and barrier height inhomogeneities accounts for the measured electrical characteristics until flat bands are reached, in accordance with a model which generalizes that by Tung [Phys. Rev. B 45, 13509 (1992)] and permits to extract physically meaningful parameters of the three kinds of interface: (a) unannealed ones, (b) annealed at 350 °C, (c) annealed at 450 °C with the characteristic barrier heights of 2.2–2.5 V in case (a) while as low as 0.96 V in case (c). Possible models of potential barriers for several metals deposited on well defined oxygen-terminated diamond surfaces are discussed and compared to experimental data. It is concluded that interface dipoles of several kinds present at these compound interfaces and their chemical evolution due to annealing are the suitable ingredients that are able to account for the Mott-Schottky behavior when the effect of the metal work function is ignored, and to justify the reverted slope observed regarding metal work function, in contrast to the trend always reported for all other metal-semiconductor interfaces.

Diamond metal-oxide-semiconductor capacitors were prepared using atomic layer deposition at 250 °C of Al2O3 on oxygen-terminated boron doped (001) diamond. Their electrical properties were investigated in terms of capacitance and current versus voltage measurements. Performing X-ray photoelectron spectroscopy based on the measured core level energies and valence band maxima, the interfacial energy band diagram configuration of the Al2O3/O-diamond is established. The band diagram alignment is concluded to be of type I with valence band offset ΔEv of 1.34 ± 0.2 eV and conduction band offset ΔEc of 0.56 ± 0.2 eV considering an Al2O3 energy band gap of 7.4 eV. The agreement with electrical measurement and the ability to perform a MOS transistor are discussed.

Metal and oxide distribution in diamond metal–oxide–semiconductor (MOS) structures are characterized using several transmission electron microscopy (TEM) modes at nanometric scale. To understand their electrical behavior, oxygen distribution using electron energy loss spectroscopy (EELS) through the layer structure, high‐resolution electron microscopy (HREM), and annular dark field (ADF) observations are reported. Oxide thickness variations, as well as oxygen content variations have been identified and characterized at an atomic resolution. The latter allows to understand the related electrical behavior as, for example, leakages or shortcuts.

In the view of predicting the performances as well as anticipating the architecture of the future diamond devices, it is of fundamental importance to accurately implement the physical properties of diamond into finite element based software. In this context, we used Silvaco to model a diamond p–n junction and studied the carrier densities responsible for the electrical characteristics of the devices. The simulated electrical characteristics are compared to experimental data and the influence of Shockley–Read–Hall and Auger recombination models on the carrier densities and J(V) characteristics was investigated. The bias voltage boundary between low and high injection conditions, Ψbi=4.7eV, was well reproduced. However, the extremely low calculated carrier densities lead to extremely low current densities in the low injection regime, reaching the numerical precision limit. The simulation of the reverse characteristic predicts a breakdown voltage of 225V. Preliminary results on hopping conductivity implementation into the simulation tool are presented. Eventually, these results will be used to predict the architecture and behavior of future devices, such as bipolar junction transistor and metal–oxide–semiconductor field effect transistor.

Metal-oxide-semiconductor structures with aluminum oxide as insulator and p-type (100) mono-crystalline diamond as semiconductor have been fabricated and investigated by capacitance versus voltage and current versus voltage measurements. The aluminum oxide dielectric was deposited using low temperature atomic layer deposition on an oxygenated diamond surface. The capacitance voltage measurements demonstrate that accumulation, depletion, and deep depletion regimes can be controlled by the bias voltage, opening the route for diamond metal-oxide-semiconductor field effect transistor. A band diagram is proposed and discussed.

Diamond is not only known for being the hardest gemstone but also for being the semiconductor having the highest calculated figures of merit (FOM). This comes from the unique physical properties of this material. Thus, it is predicted that diamond should exceeds silicon carbide (SiC) and galium nitride (GaN) in terms of low loss device and better compromises for on-state resistance versus breakdown voltage. However, in practice the applications of diamond devices are still limited and the performances are still not reaching the theoretical predictions. The question is then how to predict and evaluate diamond device performances themselves and in their environment. One of the possible answer is by using finite element based softwares. Few reports exist on unipolar diamond device modeling, and none on diamond bipolar device. The main limitations come from the lack of parameters implemented in the simulation tools together with the difficulties for modeling wide band gap semiconductor, i.e. extremely low carrier concentrations. In this study, we present the results on the first simulation of a diamond bipolar junction transistor electrical characteristics. The validation of the simulation is the first step towards the prediction of the architecture and behavior of future diamond devices.