Real-time extraction of growth rates from rotating substrates during molecular-beam epitaxy

Abstract

We present a method for measuring molecular-beam epitaxy growth rates in near real-time on rotating substrates. This is done by digitizing a video image of the reflection high-energy electron diffraction screen, automatically tracking and measuring the specular spot width, and using numerical techniques to filter the resulting signal. The digitization and image and signal processing take approximately 0.4 s to accomplish, so this technique offers the molecular-beam epitaxy grower the ability to actively adjust growth times in order to deposit a desired layer thickness. The measurement has a demonstrated precision of approximately 2%, which is sufficient to allow active control of epilayer thickness by counting monolayers as they are deposited. When postgrowth techniques, such as frequency domain analysis, are also used, the reflection high-energy electron diffraction measurement of layer thickness on rotating substrates improves to a precision of better than 1%. Since all of the components in the system described are commercially available, duplication is straightforward.

Reflection high-energy electron diffraction during substrate rotation: A new dimension forin situcharacterization

“…[1][2][3][4] The results demonstrate that it is possible to extract the growth rate by extracting the RHEED oscillation signal. These approaches are either based on intensity measurements combined with Fourier filtering, 1,5 and high frequency rotation 2 or measurements of the specular spot size combined with Fourier filtering.…”

“…These approaches are either based on intensity measurements combined with Fourier filtering, 1,5 and high frequency rotation 2 or measurements of the specular spot size combined with Fourier filtering. 3 Even if the RHEED oscillations are not evaluated, the specular spot intensity varies depending on the growth conditions used and can be used to characterize MBE growth. 4 RHEED measurements on nonrotating substrates, apart from growth rate determination 6 and characterization of interfaces 7 using RHEED oscillations, also use the information contained in the geometry and shape of the diffraction streaks to assess the surface structure in MBE.…”

Reflection high-energy electron diffraction oscillations on rotating substrates

“…A different method uses a spot tracking algorithm combined with numerical filtering techniques to determine the specular spot size and measure its variations during growth. 10 The signal in this case is quite noisy and a narrow filter window needs to be applied to determine the growth frequency, which means that the growth frequency has to be known quite accurately before the measurement. The use of the specular spot size or full width at half maximum ͑FWHM͒, though, is advantageous, since this signal typically varies by not more than one order of magnitude, allowing simple and fast processing of the digitized data.…”