Boron doped diamond

Abstract

A layer of single crystal boron doped diamond produced by CVD and having a total boron concentration which is uniform. The layer is formed from a single growth sector, or has a thickness exceeding 100 μm, or has a volume exceeding 1 mm3, or a combination of such characteristics.

Description

[0001] This is a divisional application of U.S. application Ser. No. 10 / 653,419, filed Sep. 3, 2003, which is a continuation of U.S. application Ser. No. 10 / 319,573, filed Dec. 16, 2002.BACKGROUND OF THE INVENTION [0002] This invention relates to doped diamond and more particularly to doped diamond produced by chemical vapour deposition (hereinafter referred to as CVD diamond). [0003] There are a range of applications of diamond for which a doped diamond layer of significant dimensions, with a uniform dopant concentration and associated electronic and / or optical properties would be advantageous. Dependent on the detailed application, this material needs to substantially exclude detrimental electronic or optically active traps or defects. To date, material of this type has not been available. [0004] Applications such as high power electronics require bulk free standing diamond with thicknesses ranging from 50 to 1000 μm and lateral sizes varying from 1×1 mm2 to 50×50 mm2. For viable ...

AI Technical Summary

Benefits of technology

[0032] The method of the invention may additionally include the use of controlled nitrogen additions to the source gas. The nitrogen in the source gas provides an additional means of control of the morphology developed by the growing single crystal, and the incorporation ratio for nitrogen is substantially lower than that for boron. Thus nitrogen additions, calculated as molecular nitrogen, in the range greater than 0.5 ppm and less than 10000 ppm, and preferably in the range greater than 1 ppm and less than 1000 ppm, and more preferably in the range greater than 3 ppm and less than 200 ppm do not adversely affect the electronic properties of the boron doped layer significantly, since the doped material intentionally has boron present as a scattering centre, but does enhance the size of the {100} growth sector and reduce the size of competing growth sectors such as the {111}. This means that, for growth on a {100} plate, the addition of nitrogen enables the growth to remain substantially {100} growth sector. Those skilled in the art will appreciate that the stage of using nitrogen to modify the morphology, and the stage of growing the uniformly boron doped layer may be separated or sequential.

[0033] The uniformly boron doped diamond of the invention thus enables a wide range of applications in areas such as electronic, detectors, high power electronics etc. In addition, there are other applications where the uniformity in the colour, luminescence, or other properties associated with uniform boron doping is advantageous. For example, in certain applications such as a cutting blade, boron may be used to colour the diamond thus improving visual control, and uniformity in the colour can be perceived as a factor indicating quality. Alternatively the diamond may be used in decorative applications such as polished gemstones, where uniformity in colour is again generally perceived as a quality factor.

Problems solved by technology

To date, material of this type has not been available.

Other potentially shallow dopants reported in the literature to be under investigation include S, P, O, Li, but these are not yet available as reliable bulk dopants.

However, the incorporation of boron during synthesis is a very sensitive property of the particular growth sector.

The only currently reliable post growth treatment applicable to diamond is ion implantation, and this provides a method of producing layered diamond structures, but not uniform bulk doping.

Unfortunately residual damage (vacancies and interstitials) is always created under conditions of ion implantation.

This damage is impossible to remove completely, although annealing treatments can reduce it.

The damage leads to degraded charge carrier properties resulting from defect scattering and compensation of boron acceptors.

Diamond films have also been doped unintentionally when, for example, the plasma has decomposed a substrate holder fabricated from hexagonal boron nitride.