Reflection high-energy electron diffraction intensity oscillations during molecular-beam epitaxy on rotating substrates

Abstract

We report the gated detection of reflection high-energy electron diffraction (RHEED) signal intensity oscillations during molecular-beam epitaxy (MBE) while the wafer is being rotated at high speed (≳100 rpm). In general, a larger number of oscillation periods are observed with this technique than during stationary measurement because of the very high growth rate uniformity across the sample. We found that the average over all azimuths of the RHEED specular spot intensity shows the same growth induced oscillations. This allowed us to replace the gated detection by an averaging detection method: a low-pass filter suppresses fast variations due to rapid changes in azimuth, while passing low-frequency (<1 Hz) growth related oscillations. This simplifies the detection system and at the same time reduces noise related to wafer motion, 60 Hz, etc. These techniques have potential use for in situ monitoring of thickness and composition of device wafers.

MBE-Grown CdTe Layers on GaAs with In-assisted Thermal Deoxidation

“…10 Figure 1 shows the RHEED images of the epiready surface and thermal deoxidation effects under As 4 and In overpressures. Bright and streaky spots became discernible after both As 4 -and In-assisted deoxidation processes.…”

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. 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.…”

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

“…A similar approach has been implemented using custom-built hardware. 4 However, a software based method is vastly superior in its flexibility since it allows the MBE operator to tailor the filter for a particular rotation and growth rate. In addition, with a sophisticated numerical filtering technique the software approach is easily fast enough to allow real-time data collection.…”

“…van der Wagt et al demonstrated another technique for growth rate measurements on a rotating substrate. 4 They used high speed substrate rotation ͑ϳ400 rpm for growth rates of 1 ml/s͒ and a custom-built electrical filter to separate specular spot intensity variations due to rotation from those due to epilayer growth. They were successful in extracting the growth oscillations; however, the high speed rotation which the authors said led to excessive wear and the custom circuitry limited the application of their technique.…”