Research / Systems

The UCSB MBE Lab currently has eight operational systems:

System C

System C is a horizontal reactor with 8 ports plus a dual gas injector/pyrometry port. As of 3/3/2008, available materials are: Al, Ga, In, Er, As, Sb, Si, Be, and CBr4. In addition, there is an e-beam evaporation chamber attached under UHV, allowing the deposition of thin films of Mo and possibly W. A thermally cracked hydrogen station allows desorption of native oxides from GaSb and similar wafers without melting them.

Recent activity on System C includes: ErAs nanoparticles and films on GaAs and InGaAs for physics, tunnel junctions, and thermoelectrics, High-mobility channels for InGaAs MOSFETs are also grown on this machine, as are record low resistance ohmic contacts to InGaAs and InAs for next-generation MOSFETs and HBTs.

GEN III

This Gen III system is a horizontal reactor with 12 source ports. As of 1/23/2019, the available sources are Ga, In, Al, As, Sb, Er, Si, and Be, which are all solids, and one gas source, CBr4, used for doping. This system is mainly used to grow group III-Vs including aresenides and antimonides. In the past, it was used to research vertical-cavity surface-emitting lasers (VCSELs) and rare earth thermoelectric materials.

Currently, this system is used to study quantum dot lasers, micropillars with coupled quantum dots for cavity quantum electrodynamics, and Er:In(Al,Ga)As for THz devices. This Gen III system has an integrated spectrometer for band edge thermometry and in-situ growth rate monitoring. This system belongs to John Bowers' research group.

Spintronics

Spintronics is an Applied Epi (Veeco) Gen II horizontal reactor with 8 ports plus a band-edge thermometry/pyrometry port. As of 10/24/2008, available materials are: Al, Ga, In, Mn, As, Cr, Si, and Be. The transmission band-edge thermometry system allows for accurate, reproducible control of the substrate temperature 400° below normal; this capability is useful for highly non-equilibrium growth of alloys such as GaMnAs, a ferromagnetic semiconductor.

Recent activity on Spintronics includes: optical studies of quantum-confined GaMnAs in the far-paramagnetic regime and studies of bulk (~100 nm) films of GaMnAs in the far-ferromagnetic regime.

Nitride GEN II

The plasma nitride system is a Varian Gen II horizontal reactor with 8 source ports plus a pyrometry port. As of 1/23/2019, the available sources are Ga, In, Al, Mg (p-dopant), Si (n-dopant), and two RF-plasma nitrogen units. One of the plasma sources is used for traditional growth rates of 0.3um/hr, and the other is for growth rates of up to 3 um/hr. There are three pumps in the main chamber, two cryo pumps and one ion pump. The system also has a custom built gas injector for CBr4 and BBr3, which was design and made by John English, making it unique in the world. Some past accomplishments done on this system include: reaching world record mobility for GaN, researching and achieving outstanding GaN/AlGaN HEMTs (high electron mobility transistors) performance, demonstrating growth rates above 7.6 um/hr, and creating the highest structural quality of BGaN using MBE. The Nitride Gen II system is capable of growth rates previously inaccessible to nitride PAMBE (plasma-assisted molecular beam epitaxy) because of its high growth rate plasma unit. It is also capable of growing at low temperatures, which enables high composition InGaN and even pure InN.

This system is currently used for research with James Speck's group and Umesh Mishra's group. The substrates used in this system are GaN on sapphire and free-standing GaN, SiC, ZnO. Current research topics on this system include: growing AlN/AlGaN on SiC for UVLED, reaching high N-flux InGaN for better light emitters and electronics, growing InGaN on ZnO for electronics, and electronics with GaN/AlGaN.

Nitride 930

The Nitride 930 is a tilted Veeco 930 reactor with 8 main source ports and is mainly used to grow III-nitrides. As of 1/23/2019, the available solid sources are Si, Ge, Mg, Ga, In, Al. The available gas sources are N2 plasma, NH3, and CBr4, which serves to provide carbon to the system. Gas filters are used for both nitrogen source to achieve high purity. The In, Al, two Ga, as well as the ammonia source, are most often used for the current research work. Though not as toxic as arsenide, dealing with the ammonia in this system can be difficult because, during growth, ammonia will freeze on the cryo-panel in the reactor, leaving ammonia ice which is easily identifiable by its green color. A recovery process will take place every two weeks on this system to "boil off" the ammonia ice build up by pausing the liquid nitrogen flow and heating up the cryo-panel in a controlled way. In the main chamber of the Nitride 930, there is an ion pump, a cryo-pump, and a turbo pump which is used to deal with high gas loads during the recovery process. In the buffer chamber, there is another ion pump. The current research done using this system are regarding tunnel junctions, UV LED, diodes, and p-transport studies. This system belongs to Professor James Speck's research group.

Oxide 930 (1)

This newer Oxide 930 (Veeco) system in the UCSB MBE lab has 8 ports plus a oxygen plasma unit. As of 1/23/2019, the available solid sources are Sr, Ba, Sm, Gd, La, Eu, Ti and Ru. The sources, Ti and Ru, are used to create the organometallic precursors, tetraisopropoxide (TTiP) and ruthenium tetroxide (ZTB), which are advantageous for thin-film growth of metals and metal oxides. This system is currently working with strongly correlated materials, or insulators and electronic materials in the group of heavy fermion compounds. It is primarily used for research in superconductivity and magnetotransport, or the transport of electrons through metals and semiconductors in a magnetic field. This system belongs to Professor Susanne Stemmer's research group.

Oxide 930 (2)

This Oxide 930 is a horizontal reactor with 9 source ports used to grow complex oxides. As of 1/23/2019, the available solid sources are Ba, Sr, and SnO2. The liquid sources are Sn and La, which is used as a dopant. The gas sources are TTiP and O2 plasma. This system uses two SnO2 cells to grow oxides as well as tin oxide powder, which can be harmful to the machine because it corrodes the interior of the reactor. In the recent years, this Oxide 930 mainly grew BaSnO3, SrTiO3, and BaTiO3. In the main chamber of this system, there is a cryo pump, cryo panel, and turbo pump. This system also has oxidation resistant cells and a beam flux monitor (BFM) that calibrates the flux of the effusion cell and checks the flux ratios of the different sources. Currently, the research done with this system is focused on growing BaSnO3 with high mobility by using different techniques, such as changing growth conditions, growing on different substrates, and growing topological materials like Ba3SnO or Sr3SnO. This system belongs to Susanne Stemmer's research group.

Oxide 620

The Oxide 620 is a vertical reactor with 6 source ports and a plasma-assisted molecular beam epitaxy (PAMBE) system. As of 1/23/2019, the available solid sources are Ga, Sn, In, Al, and Mg, but they are melted into liquids when operating, except for Mg, which stays as a solid. It also uses a RF-plasma source for oxygen. In the past, this system was used mostly for research of SnO2 (tin oxide) and Ga2O3 (gallium oxide).

Currently, the main growths done on this system are Ga2O3 and metal alloys with Ga, In, and Al. Ga2O3 is a wide band gap semiconductor with the potential of improving power electronics, so these films are grown and analyzed to understand its basic material properties. Other applications of this system include: doping heterostructures and device structures, studying Modulation Doped Field-Effect Transistors (MODFETs). This Oxide 620 system is belongs to James Speck's research group.

CdAs GenII

This Gen II system is a horizontal reactor with 8 source ports and is used mainly for Cd3As2 (cadmium arsenide), which is a semi-metal, and other III-V semiconductors. In the past, this system was used for the research and growth of materials such as MgO (magnesium oxide) and Ga2O3 (gallium oxide). As of 1/23/2019, the available sources are Ga, In, Al, Sb, and As. It uses 2 cells for Cd3As2 to get accurate vapor pressure measurements. This system also has Sb and As cracker cells, which produces Sb2 molecules that are used to create buffer layers, ensuring that the surface of the films are stable for growing Cd3As2. The buffer layer can be GaSb (gallium antimonide) or InGaSb (indium gallium antimonide), and it reduces mismatches between the film and substrates that contain some impurities.

This system is capable of growing high qualify films of Cd3As2 and some group III-V materials like GaSb (gallium antimonide). It also has a hydrogen etching system that cleans and prepares substrates, which allows the system to grow with Al materials as well. Currently, this Gen II machine grows Cd3As2 experimentally to research its physical properties because it has the potential to be applied in many areas such as electronics, quantum computers, and infrared detectors. This system belongs to Susanne Stemmer's research group.

Compact 21

The Compact 21 system is a vertical style MBE and is the newest MBE system at UCSB. Since arriving in mid 2018, the system has been used to explore growth of IV-VI semiconductors on III-V substrates. At present there are two compound IV-VI sources installed, PbSe and SnSe, in addition to a subset of III-V sources and a Se source for assisting in IV-VI growth. Growing IV-VI semiconductors on III-V substrates poses some distinct challenges, as the two classes of materials have different crystal structures, valency, and bonding behavior, which makes for non-trivial growth interfaces. Current work on this system focuses on growth of PbSnSe for optoelectronic applications, SnSe for thermoelectric applications, and future work will explore the properties of topological insulators like cubic SnSe and Sn-rich PbSnSe. This system belongs to Kunal Mukherjee's research group.

VG V80H III-V/Metals

The Oxide 620 is a vertical reactor with 6 source ports and currently 5 sources. The 5 sources are Sn, In, Sb, Ga, and an oxygen rf-plasma source.

Metals

The Oxide 620 is a vertical reactor with 6 source ports and currently 5 sources. The 5 sources are Sn, In, Sb, Ga, and an oxygen rf-plasma source.

Heusler GEN II

The Oxide 620 is a vertical reactor with 6 source ports and currently 5 sources. The 5 sources are Sn, In, Sb, Ga, and an oxygen rf-plasma source.

Veeco Oxide

The Oxide 620 is a vertical reactor with 6 source ports and currently 5 sources. The 5 sources are Sn, In, Sb, Ga, and an oxygen rf-plasma source.