Optical measurement of Ga beam flux for MBE

Real-time in-situ flux monitoring by wavelength-modulated atomic absorption spectroscopy in molecular beam epitaxy: Application to Ga flux measurement

“…Their respective absorption strength [14] and distribution of the initial and final state of the transition at the usual Ga-cell temperature [15] are almost identical. Both have been used for previous fixed wavelength measurement, either at 403.3 nm [3,4] or at 417.2 nm [7][8][9]. So, the main criterion to choose one of these wavelengths is that the 417.2 nm line was too close to the commercial nitride laser upper wavelength limit: the 403.3 nm line has thus be preferred.…”

“…To reach a sufficient sensitivity, complicated optics had to be used to increase the atomic absorption, for example through a double-pass of the optical beam inside the MBE chamber [7,8]. Apart from these absorption experiments, it must also be mentioned that Ga flux monitoring has been achieved by means of fluorescence measurements, although some difficulties have apparently prevented a further use of this technique [9]. An efficient way of overcoming the sensitivity problem inherent to direct transmission measurements is by modulating the wavelength (WMAAS).…”

Monitoring and Control in Vapor phase Epitaxy

“…Several groups have adapted atomic absorption spectroscopy to measure and stabilize the flux of group-III metals in molecular-beam epitaxy. [5,6] Atomic fluorescence has a sensitivity approximately four orders of magnitude higher because it is a measurement of a signal against zero background, while an absorption measurement involves the detection of a small intensity loss in a large background probe beam.…”

Development of a fluorescence based flux sensor for thin film growth and nanoparticle deposition

“…Alternatively, the fluorescent signal of nanoparticles can be used to obtain a very fine control of the deposition rate. One of these ideas, proposed already some time ago, is to use a laser induced fluorescence intensity [8][9][10]. In this paper, flux measurements are demonstrated on two different test systems.…”