Diamond synthesis can be achieved through several routes. The two main methods are high-pressure high-temperature synthesis (HPHT) and chemical vapour deposition (CVD).

Diamond synthesis can be achieved through several routes. The two main methods are high-pressure high-temperature synthesis (HPHT) and chemical vapour deposition (CVD). HPHT diamond is commonly used today in many industrial applications including: cutting, drilling, thermal management etc. However, HPHT diamond invariably contains many crystal defects and impurities. CVD diamond, on the other hand, can be grown under conditions of high purity resulting in fewer impurities. Unfortunately, the deposition conditions have invariably resulted in polycrystalline material. It was only recently shown that it is possible to grow thick free-standing plates of high-purity single-crystal CVD (SCCVD) diamond by homoepitaxy. To a great extent the interest in high-purity SCCVD diamond has been driven by the desire to develop diamond as a semiconductor material for electronic device applications. To achieve high activation in a doped semiconductor it is necessary to have a low degree of compensation. For p-doped material, for instance, the amount of compensating donors (shallow or deep) must be kept to a minimum. This puts strict demands on the impurity concentration of the material. Successful p-doping of diamond by adding boron during deposition has been demonstrated. Concentrations of nitrogen impurities < 1014 cm-3 have also been achieved, leading to low compensation levels.

Schematic setup of a “Belt” apparatus for the production of HPHT synthetic diamonds

Rough HPHT synthetic diamond

Schematic setup of a system for the production of CVD synthetic diamond.

Polished CVD synthetic diamond

微波CVD法制备的各种单晶钻石（打磨抛光后的）

CVD Diamond

ChemicalVaporDeposition (CVD) diamond is manufactured by means of a diamond synthesis technology in which a low pressure reactor is used to combine a thermal or plasma activating agent with a gas-phase carbon to produce a chemical reaction which results in polycrystalline diamond crystal growth or deposition upon a solid surface or substrate.

Although not a new concept (CVD diamond synthesis was first introduced by scientists over 50 years ago) it is only within the last decade that CVD diamond synthesis has shown its potential to become a commercially and economically viable alternative to natural diamond in the workplace, able to be grown in a controlled environment to desired thicknesses of up to ~2mm. CVD diamond wafers can also be cut into a variety of shapes and polished to achieve mirror-like finishes if required.

CVD Diamond Grades & Applications

Optical Grade CVD Diamond– High purity & transparency (transmission 65% @ 8-10µm).IR (Infra-red) Windows

Thermal Grade CVD Diamond– High hardness & thermal conductivity (>12W/cmK).Heat SpreaderIC (Integrated Circuit)LD (Laser Diode)LDA (Laser Diode Array) for thermal management

Mechanical Grade CVD Diamond– High hardness, good tensile strength & fracture toughness.Dressing Tools– Single & multipoint dressers; grinding wheel dressers.Cutting Tools- Surgical knives; cutting tool inserts; drill bits; reamers etc.Wear Resistant Coatings– Non-ferrous, plastic and composite materials.Wire Dies – Wire die blanks for hard metal wire e.g. tungsten, molybdenum & stainless steel.

CVD法制备的单晶金刚石（微波法制备）

A single crystal CVD diamond plate

Comparison of common semiconductor materials:
 x-axis: Bandgap; y-axis: Combined electron + hole mobility;
 Area of circles proportional to thermal conductivity.

Optical grade diamond window

ScienceDaily (Feb. 26, 2004)— Washington, D.C. -- Producing a material that is harder than natural diamond has been a goal of materials science for decades. Now a group* headed by scientists at the Carnegie Institution's Geophysical Laboratory in Washington, D.C., has produced gem-sized diamonds that are harder than any other crystals. Further, the researchers grew these diamonds directly from a gas mixture at a rate that is up to 100 times faster than other methods used to date.

This photograph shows a synthetic brilliant cut single-crystal diamond grown by chemical vapor deposition, CVD. About 2.5 mm high, this crystal was grown in about 1 day at Carnegie. The very bottom (table) of the crystal is a type 1b seed: hence the yellow tint which is due to internal reflection (the CVD diamond is transparent). [C.S. Yan et al., Physica Status Solidi (a) 201,R25 (2004)]. The researchers have also reported that these CVD diamonds are capable of easily generating ultrahigh pressures to at least 200 GPa. [W.L. Mao et al., Appl. Phys. Lett. 83, 5190 (2003)] (Image used with permission Physica Status Solidi http://www.pss-rapid.com) .

微波CVD法制备的各色单晶钻石

 Gemological and spectroscopic properties of 43 CVD synthetic diamonds from Apollo Diamond Inc. were examined to characterize the latest generation of their CVD products. These samples, which included both faceted gems and partially polished crystals, were provided as representative examples of Apollo’s 2006–2007 production. Relative to the Apollo CVD products examined in 2003, the new samples showed significant improvements in size, color, and clarity. In addition to colorless and near-colorless material, fancy orange-to-pink colors are now produced. These high-quality CVD-grown diamonds, comparable in color and clarity to natural diamonds, can be identified using a combination of gemological and spectroscopic properties.