High Uniformity Thick Film  of Single-Crystal Diamond: Morphology, Quality, and Device Properties

Abstract

MPCVD is the most effective method for growing inch-scale diamond wafers, but traditional growth processes result in edge polycrystallization and reduced effective area with increased thickness. Additionally, there is a trade-off between quality and growth rate. In this paper, the main challenges of decreasing crystal quality and inward shrinking of the single-crystal area after thick-film growth has been addressed. Under specific substrate-to-substrate holder area ratios and temperature conditions, seven high quality diamond samples up to 4.5 mm thick without a polycrystalline rim were obtained. The boule sample with the largest area gain was laser-cut into seven pieces, all of which demonstrated exceptional uniformity, with XRD rocking curve FWHM values below 77 arcsec and deviations of less than 7 arcsec between them. Similarly, the Raman FWHM values were below 2.1 cm⁻¹, with deviations less than 0.1 cm⁻¹. What’s more, Hydrogen-terminated diamond field-effect transistors (FETs) fabricated on these substrates exhibited high electrical performance, with current densities exceeding 90 mA/mm, on/off ratios greater than 109, and mobilities over 76 cm²/(V·S). The preparation of uniform and high-quality thick films offers a reliable approach for fabricating large-scale, high-quality diamond thick films. This advancement significantly broadens their potential applications in electronic and optoelectronic devices.

Keywords: MPCVD, Single crystal diamond thick films, Uniformity, High quality, Field effect transistor, Device properties