Molecular Beam Epitaxy (MBE), Atomic Layer Deposition (ALD), and in-situ X-Ray Photoelectron Spectroscopy Laboratory

The Hinkle group has established a cluster tool laboratory that enables state-of-the-art in-situ materials growth and characterization capabilities encompassing five separate MBE chambers (chalcogenide growth chamber, oxide growth chamber, nitride growth chamber, arsenide growth chamber, and group IV materials growth chamber), one MOCVD system (currently set up for nitrides), atomic layer deposition (ALD), and integrated analysis tools. The system utilizes 50 mm diameter wafers (for cleanroom process compatibility), and modified sample plates for the various deposition and characterization techniques. Wafers are transported throughout the system in a UHV transfer tube. Each deposition module has substrate heating and rotational capability for control of film uniformity and growth kinetics in addition to diffraction capabilities for real-time analysis of the growth quality. Each chamber is fully controlled by computer and operates at a base pressure in the 10-11 mbar range indicating the extreme cleanliness of the systems. The Analytical Module is equipped with an array of analytical techniques including monochromatic XPS, UPS, and Scanning Auger Electron Spectroscopy. Small samples (2.5 cm diameter) can also be separately introduced and characterized in the analytical module under heating and cooling conditions as well as depth profiling utilizing either angle-resolved XPS or Ar-ion depth profiling with in-situ sample rotation for better depth resolution.

The Atomic Layer Deposition module is integrated onto the system through an associated buffer chamber to enable the detailed study of thin films deposited by this technologically important technique (with in-situ XPS for example). The buffer chamber provides the ability to transport wafers through the system and surmount the pressure gap between the ALD reactor and the UHV system for subsequent surface characterization or MBE deposition. Additionally, the ALD reactor is capable of direct wafer/sample insertion as well. Up to six precursors are integrated, greatly expanding the parameter space that can be explored in the proposed research.

At Notre Dame, we also have a separate dual-chamber Riber 32 MBE machine associated with the Furdyna/Liu lab. One of the chambers is dedicated to the growth of III-V-based semiconductors, and is equipped with Al, Ga, In, As, and Sb elemental sources, together with a Be doping cell for p-type co-doping and a Si doping cell for n-type co-doping, when necessary. Recently, we have installed a phosphorus cell to this chamber to enable fabrication of phosphide semiconductors. The second chamber operates with Zn, Cd, Mn, Mg, Se, and Te elemental effusion cells used for the growth of II-VI semiconductor alloys; a Bi source for Bi-compounds; a nitrogen RF plasma source for p-type doping of II-VI materials; and an Oxford Applied Research e-Beam Evaporator serving as a source of high-melting-point metals (such as Mo and W). The two chambers are inter-connected by an ultrahigh vacuum channel, allowing transfer of wafers between the two chambers without exposure to atmosphere. The facility with all the essential ancillary facilities (chemical and laminar flow hoods, dedicated liquid nitrogen supply, de-ionized water, etc.). The cell shutters in both chambers are computer-controlled, and perform reliably in MBE mode, as well as in the more demanding atomic layer epitaxy (ALE) and migration-enhanced epitaxy (MEE) modes, which are useful in growths requiring deposition with extreme precision. The MBE growth is monitored in-situ by a 10 keV RHEED gun.

In addition to specimen fabrication, we have excellent capabilities for X-ray rocking-curve and lattice parameter determination located in the same room as the MBE machine, which provide immediate feedback on the quality and composition of the layers grown by MBE. The operation of the X-ray system in tandem with the MBE growth makes this arrangement especially efficient. Additionally, for more detailed structural characterization we have access to several high-resolution XRD systems on the Notre Dame campus. The most relevant for our needs are the Bruker APEX-II 3-circle diffractometer, Bruker Kappa 3-circle diffractometer, and Bruker D8 Advanced Powder Diffraction System. All of these instruments are located in our building.