MBE1

Growth System MBE 1 (SiGe)

Paola De Padova - paola.depadova@ism.cnr.it

Carlo Ottaviani - carlo.ottaviani@ism.cnr.it

Sandro Priori - sandro.priori@ism.cnr.it

Laboratory: IC11

Rome - Tor Vergata

The heart of an MBE apparatus resides into the Knudsen effusion cells (called K-cells or effusion cells) and in a system to monitor the epitaxy and/or film crystallinity. This is, for instance, the reflection high energy electron diffraction (RHEED) system. In this case the RIBER K-cells are designed for an operating temperature up to 1200°C, pyrolytic BN, or at 1400°C C-pyrolytic BN. Conventional temperature control based on the proportional–integral–derivative (PID) device join to a thermocouple feedback, provides a temperature stability ΔT of few °C

TECHNICAL SPECIFICATIONS

Working pressure ~10-11^-11 mbar
Si(C-BN-1400 °C), Ge(BN-1200 °C, Mn(BN-1200 °C) K-cells; Si (flux=0.04 Å/min); Ge (flux=0.16 Å/min);
Sb, As, Bi- Surfactants effusion cells;
Ag, Au- Capping Layer effusion cells;
DC direct sample heating (RT-1200 °C) and Indirect heating (RT-450 °C ) systems;
Air-vacuum Fast Load-lock Sample Transfer System;
Variable e- HV (0-15 KeV) for RHEED system;
Hi-Speed Camera for real-time data diffraction acquisition (Image-software-MAC).

AVAILABLE TECHNIQUES

RHEED Ultra-High Vacuum (UHV) System for Surface Science Investigations;
Cleaning Semiconductor (SC), Metal (M)-Surfaces reconstruction;
Epitaxial growth SC/SC, SC/Metal/SC;
Homo- and Hetero-structures growth: 1D, 2D and 3D Materials.

SAMPLES

Sample lateral dimensions: 10 x 5 mm (ideal), 3 x 3 mm (minimal), 10 x 10 mm (maximal);
Sample thickness: ideally up to 2 mm (thicker and/or smaller samples also feasible).

USED FOR

Fundamental Surface Science study;
Artificial Atomic Epitaxial Growth;;
Discovery of new 1D, 2D and 3D epitaxial SC/SC; M/SC for micro-nanoelectronics and solar cells purposes;
Semiconductors for Microelectronics;
Microcircuits;
Ultra-thin Films;
Samples Cleaning;
Thin-film Stability;
Barrier Layers;
Lubrication;
Chemical Industry;
Coatings/Catalysis.

CASE STUDIES

Cross-sectional high-resolution transmission electron microscopy (HRTEM) image of a Mn0.06Ge0.94 film grown on a Ge(001)2✕1 substrate held at 520 K_0.06Ge_0.94 on Ge(001)2✕1

The structural, electronic, and magnetic properties of the Mn0.06Ge0.94 diluted magnetic semiconductor_0.06Ge_0.94, grown at 520 K by molecular-beam epitaxy on Ge(001)2✕1, have been investigated. Diluted and highly ordered alloys, containing Mn5Ge3 nanocrystals₅Ge₃. The valence band photoelectron spectrum of Mn_0.06Ge_0.94 shows a feature located at −4.2 eV below the Fermi level, which is the fingerprint of substitutional Mn atoms in the Ge matrix. Magnetization measurements show the presence of a paramagnetic component due to substitutional Mn atoms and of a ferromagnetic like component due to Mn₅Ge₃. The Mn L2,3 x-ray absorption spectrum of this polyphase film shows no marked multiplet structure, but a bandlike character.

See: P. De Padova, et al., Phys. Rev. B 77, 045203 (2008).

Immagine ad alta risoluzione in sezione-trasmessa ottenuta al microscopio elettronico a trasmissione (HRTEM) sul film di Mn_0.06Ge_0.94 cresciuto sul substrato di Ge(001)2✕1 tenuto ad una temperatura di 520 K.

Immagine ad alta risoluzione in sezione-trasmessa ottenuta al microscopio elettronico a trasmissione (HRTEM) di un film di Mn₅Ge₃ cresciuto sul substrato di Ge(111), misurata lungo la direzione di asse di zona [-1-12] del substrato di Ge(111). (b) Vista laterale a sfere e sticks di un'epitassia coerente tra il film di Mn₅Ge₃ e il substrato di Ge.

Spettri di assorbimento a raggi-X di L_2,3 di Mn misurati per polarizzazione circolare della luce destra [σ⁺ (linea rossa)] and sinistra [σ⁻ (blue dashed line)] e il corrispondente segnale XMCD (σ⁺ − σ⁻) (linea nera).

See: W. Ndiaye et al., Phys. Rev. B 91, 125118 (2015).

Mn₅Ge₃ film on Ge(111)

An investigation of the structural, magnetic and electronic properties of≈3 nm thick Mn₅Ge₃ grown on a Ge(111)-c(2✕8) reconstructed surface is reported. High resolution transmission electron microscopy and selected area electron diffraction give evidence of 2.2% in-plane compressive strain between the Mn₅Ge₃ and the Ge substrate. Magneto optical Kerr effect measurements show that the films are ferromagnetic with a Curie temperature of ≈325 K. The analysis of Ge 3d core level photoelectron spectra of the Mn₅Ge₃ allows determining an upper limit of 76 meV for the Ge 3d5/2 core-hole lifetime broadening Ge 3d_5/2. The Ge 3d3/2 core-hole lifetime broadening is found to be 15 meV larger than that of the Ge 3d5/2 core hole_3/2 _5/2, because of the existence of a Coster–Kronig decay channel due to the metallic character of Mn5₅Ge₃.