Boron concentration profiling by high angle annular dark field-scanning transmission electron microscopy in homoepitaxial δ-doped diamond layers

Abstract

To develop further diamond related devices, the concentration and spatial location of dopants should be controlled down to the nanometer scale. Scanning transmission electron microscopy using the high angle annular dark field mode is shown to be sensitive to boron doping in diamond epilayers. An analytical procedure is described, whereby local boron concentrations above 1020 cm−3 were quantitatively derived down to nanometer resolution from the signal dependence on thickness and boron content. Experimental boron local doping profiles measured on diamond p−/p++/p− multilayers are compared to macroscopic profiles obtained by secondary ion mass spectrometry, avoiding reported artefacts.

Electronic and physico-chemical properties of nanometric boron delta-doped diamond structures

“…The grey scale "noise"-in this STEM-HAADF image is attributed to a residual amorphous overlayer and to local lamella thickness variations. 30 As can be seen in Figs. 6(b) and 6(c), the nanometric scale was reached.…”

“…This means that the real thickness is probably even lower than that deduced above. Note that here a quantitative boron doping profile deduced from such profiles, as recently published using a STEM-HAADF based method, 30 was not derived as this ground value of the profile was not reached so that the inferred doping maximum value would be erroneous. An alternative would be to use atomic resolution STEM-HAADF with a much lower beam spot size, but the difficulties in preparing sufficiently thin FIB-machined lamella without any amorphization prevented us from obtaining the required atomic contrasts.…”

“…The sample was prepared with a Quanta 200 3D focused ion beam, with a final thickness of approximately 70 nm as detailed elsewhere. 30 Spectroscopic ellipsometry measurements were made taking advantage of the difference in refractive indices of NiD and p þþ diamond: these were performed from 250 to 1000 nm in air using a Woollam M-2000 ellipsometer. The experimental spectra were fitted to numerical simulations as described elsewhere 32 in order to determine the respective thicknesses of the NiD and p þþ layers present in the alternating NiD/p þþ /NiD multilayers.…”

Critical boron-doping levels for generation of dislocations in synthetic diamond

“…Thin p þ layers can act as barriers to dislocations propagation, because the high boron concentration increases the probability that a dislocation meets an interstitial or a boron pair on its way, and stops its extension during crystal growth. Epilayers grown under h100i directions in this reactor are usually fully strained 37 up to tens of micrometers thickness 38 and free of dislocations 36 (except for those from the substrate), similar to sample D.…”

“…This sample grown along h001i is composed of four p þ layers (labeled from F-16.1 to F-16.4) separated by p À layers, where the boron concentration was kept below 10 16 at/cm 3 . The grey contrast between p þ and p À layers has a chemical origin, and it is used to quantify the boron enrichment 36 above 10 20 at/cm 3 . This chemical contrast coexists with the contrast induced by dislocations in the present DF configuration.…”