Diamond power devices. Concepts and limits

Diamond is a unique material with several outstanding physical and chemical properties. It has the highest thermal conductivity at room temperature and it is transparent from the UV to the far IR. Furthermore it has the highest hardness, the highest Young's modulus and it is chemically inert and radiation hard. These and other properties of diamond are of great interest for various commercial applications. Much progress has been made in the last decade to produce diamond with chemical vapour deposition (CVD) techniques. Today, CVD diamond plates of more than 10 cm in diameter and more than 1 mm in thickness are commercially available whose properties, especially the optical and thermal ones, are comparable to the best single-crystal diamonds. In this overview, the historical development of CVD diamond deposition with the main focus on the most important techniques, hot-filament and microwave assisted CVD, will be resumed. We describe the control of structural and morphological properties during the deposition which is a prerequisite of oriented growth and the doping of diamond which is needed for semiconductor and sensor applications. The second part of this overview will discuss optical, thermal, thermomechanical and electronic properties of single-crystal diamond and CVD diamond. Finally, we give a description of several applications such as IR windows, heatspreaders, temperature sensors, piezoresistive sensors, diodes and transistors.

https://iopscience.iop.org/article/10.1088/0034-4885/61/12/002/pdf

Growth and application of undoped and doped diamond films

GE POL Diamonds: Before and After

A temperature sensor based on an array of carbon nanowires written by a 30 keV Ga+ focused ion beam on diamond substrate has been developed. The temperature sensitivity of the electrical conductuctance between the nanowires is explained by the thermal activation of charge carriers in a heterostructure graphite-diamond over an energy barrier of 0.24 eV. The sensor shows an exponential increase of current with temperature at a rate of 0.1 dB/°C in the temperature range from 40 to 140 °C. The advantages of the novel carbon nanowire sensor are light blindness, compatibility with carbon nanotechnology, reproducibility and simplicity of fabrication. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Carbon nanowire‐based temperature sensor

Carbon nanowires written by focused ion beam on diamond surface are novel nanostructures with interesting electronic properties. In this communication, carbon nanowire structures working as temperature and chemical sensors are reported. The sensor structures were made as arrays of carbon nanowires written by a 30 keV focused ion beam on polycrystalline CVD diamond films. The electronic structure of a carbon nanowire array is discussed as multiple unipolar heterodiodes graphite-diamond-graphite (G-D-G). The energy barrier of the G-D-G diodes has been found of a value 0.25 eV. The structures exhibited changes in conductance when measured at different temperatures or when put in proximity of some volatile liquids. This temperature and chemical sensitivity is explained by the activation of the charge carrier flow over the G-D barrier caused by temperature or by the charge of the analyte molecules adsorbed on the surface of the structure. The temperature response of the sensors in the range from 40 to 140 is exponential at a rate of 0.11 . The chemical sensitivity has been found selective and particularly pronounced for water vapor. The advantages of the novel carbon nanowire sensors are their blindness to visible light, compatibility with carbon nanotechnology, simplicity and reproducibility of fabrication. The all-carbon nature of the sensors implies their applicability in medicine and biology.

Temperature and Chemical Sensors Based on FIB-Written Carbon Nanowires

The main advantages of stationary luminescence as a characterization technique of diamond are its relatively simple technical realization and a wide information gained on the impuritydefect structure of crystal. The physical reasons of capability of luminescence come from a very high Debye temperature of the diamond crystal, a strong interatomic bonding, and a relatively weak electron-phonon coupling in optical centers. As a result, a majority of optical centers in diamond possess the luminescence spectra with well resolved zero-phonon lines assisted by vibration-related replica, many of them retaining this spectral structure to room temperature and even above. As zero-phonon line spectrum is normally very sensitive to any external forces applied to the crystal (temperature, mechanical stress, magnetic and electrical fields), the optical centers can serve as sensitive markers, providing much information on the state of the diamond lattice surrounding them. The value of the luminescence increases when diamond is characterized as a material for electronic and, particularly, optoelectronic applications. In this area luminescence really proves to be a unique characterization tool giving a direct information on optical and electronic properties (for instance, impurity and defect content, lifetime of charge carriers, efficiency of radiative recombination etc.), to be used in the devices. In this review the basic parameters of the luminescence centers of diamond are considered and discussed from the view-point of the information they provide. Cathodoluminescence of diamond films and ion implanted layers is given as an example of luminescent characterization of diamond. The semiconducting structures with insulating active zones are discussed as a promising application of diamond for light emitting devices operating at high temperatures.

Luminescence Characterization and Application of Diamond

The results of electrical studies on natural insulating diamonds implanted with boron ions are presented. It is shown that effective electrical activation of the boron atoms occurs at a temperature higher than 1300 °C. The effect of hole injection through the p-i junction in diamond is described. The hole mobility in insulating diamond has been measured as about 700 cm2 V−1 s−1. Using the injection properties of the p-i junction, a diode and transistor on diamond have been made by ion implantation and photolithography.

p-Type semiconducting structures in diamond implanted with boron ions

High sensitivity thermal sensors on insulating diamond

p-type semiconducting boron doped layers have been fabricated on diamond substrates by ion implantation and subsequent annealing A number of the related published experimental data and theoretical models on electrical properties of boron doped diamond are analyzed with regard to the temperature coefficient of resistance (TCR) of temperature sensors The dependencies of the conductivity and activation energy on three parameters: (i) boron doping level NA (ii) electrical compensation ratio ND/NA ≡ C and (iii) duration of the postimplantation annealing time ta are studied By variation of NA, C and ta an optimized technological regime for the temperature sensor fabrication can be obtained One can summarize that: 1) the TCR value is not remarkably reduced with the boron concentration up to NA ~ 1019 cm−3, 2) an increase of the electrical compensation decreases the activation energy and consequently the TCR coefficient, 3) 1 h annealing at 1500°C is sufficient to remove the compensating radiation defects, 4) the variation of the ta from 1 min to 1 h changes the TCR value by 20% to 30% Technological steps of the fabrication of a micro temperature sensor are given

Temperature Sensor On Boron Ion Implanted Diamond

Fabrication of various types of diamond LEDs, their characteristics and the operation mechanisms are reported. All the devices are based on the double injection electroluminescence: charge carriers are injected into intrinsic (i) diamond from adjacent semiconducting p- and n- type areas. The i-area is activated with appropriate optical centers. In the first step a survey of the appropriate optical centers and their spectra is given. The devices are fabricated in the form of either planar or vertical p-i-n or p-i-p structures. It is shown that the electrical and optical properties of the devices are controlled by the type, concentration, and spatial distribution of the deep traps in the i-region. The selection of diamond substrates suitable for the fabrication of LEDs is an essential point and it can be performed with a microwave photoconductivity technique. Several fields of possible application of diamond LEDs are shown: high temperature LEDs, optical sensors of magnetic field, color switches, color indicators of temperature, the high temperature applications being the most promising application area. Perspectives of creation of diamond based laser diodes is shortly discussed.

A. A. Melnikov

Papers

Luminescence Characterization and Application of Diamond

p-Type semiconducting structures in diamond implanted with boron ions

High sensitivity thermal sensors on insulating diamond

Temperature Sensor On Boron Ion Implanted Diamond

LEDs on diamond