LNNano - Brazilian Nanotechnology National Laboratory

Thin Film Growth Facilities

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The LCS manages equipment for thin film deposition, mainly dedicated for the growth of III-V semiconductor heterostructures. Unlike the SPM instruments, the machines are not open to external users. Never the less, we are happy to provide samples to external demand, either inside scientific collaborations or as service.


III-V Molecular beam epitaxy system

Since August 2015, the LCS runs a 2″ III-V semiconductor epitaxy chamber. The machine main chamber was constructed by Dr. Karl Eberl MBE Komponenten GmbH and existing components were integrated into the system. It currently consists of an ultra-high vacuum process chamber (base pressure ca. 5.0×10-11 mbar) with four effusion cells (Ga, Al, In, As) and two doping cells (Si,Be). Furthermore, a preparation chamber to carry out hydrogen cleaning is installed. The MBE system is automated with EpiSoft allowing to grow complex heterostructures, e.g. superlattices. RHEED images can be captured with iRHEED. The system was build with financial support of SisNANO, FAPESP and CNPq.

Structural quality of samples

A series of test samples has been grown to demonstrate the structural quality of the machine. We are able to provide high quality GaAs, InGaAs/GaAs and AlGaAs/GaAs heterostructures as well as self-assembled InAs islands.

p43_10x10 p34_1x1 P17_fit
10×10 micron AFM image of a hydrogen cleaned substrate surface with 10 ML of GaAs redeposited after cleaning. The GaAs surface is of high quality demonstrating not only the good growth of GaAs homoepitaxial material, but also our capability to clean GaAs surfaces. The sample was grown at 480°C and never under went thermal deoxidation. Surface of a AlGaAs/GaAs heterostructure. The AFM image shows an area of 1×1 micron. HR-XRD measurement of a 6x times InGaAs/GaAs superlattice. The perfect fit between the measured and the simulated curve indicates a high material quality of the InGaAs/GaAs heterostructure. The HR-XRD was carried out by Sukarno Olavo Ferreira at the Federal University of Viçosa.
002_Height_001_p46 P461x1 Dots_analysis
10×10 micron AFM image of InAs self-assembled islands grown at ca. 500°C. AFM image demonstrating the 1×1 1×1 micron area used for the dot statistic. Height distribution of the InAs dots grown at 500°C extracted with Gwyddion form the 1×1 micron AFM image. The average height is ca. 9 nm for the dots with a small standard deviation less than 1.5 nm in the height indicating good uniformity. Dot density is rather high with 53 per square micron.

Optical properties

We grown a first set of standard samples to characterize the optical quality of the epitaxial structures. Photoluminescence was carried out by Fernando Iikawa of the University of Campinas. The obtained spectra indicate a good optical quality of the samples with a low carbon background doping. The InAs island growth has to be further optimized, but the structures are optical active and of good quality.

GaAs-QW GaAs
Optical response of a GaAs quantum well in AlGaAs barriers. The well has a full width at half maximum of 2.7 nm. GaAs bulk luminescence from the GaAs quantum well sample at low excitation. We can observe the free GaAs exciton and have a low response from the carbon background doping at 830 nm indicating a low background doping level. Photoluminecense of a unstrained single mesoscopic GaAs structure. We can observe linewidth down to 180 micro-eV in such samples. Published Nanoscale Research Letters 12, 61 (2017).

Acknowledgments

Beside the members of the LCS, especially Saimon Filipe Covre, Evandro Lanzoni and Ailton Garcia Jr., we like to thank Prof. Dr. S. O. Ferreira, Prof. Dr. F. Iikawa and Prof. Dra. M. Cotta for the help during the setup. We are also grateful to the LNLS workshop and vacuum group as well as the CNPEM maintenance group for there help and contributions during installation of the MBE lab.

Setup video

See the birth of the machine:


ALD

We inherited a Cambridge Atomic layer deposition system. The system was intended to be used for in-situ growth on a beamline. Currently, we prepare the system to be opened as a user growth facility as well as defining internal projects for it. It is used to grow high quality dielectric material like TiO2 and Al2O3 for device application. For obtaining samples from the system, please contact us via e-mail.