AlGaInN Materials and Heterostructures

Molecular Beam Epitaxy Growth of GaN and Related Alloys

Task leader: Igor Berishev igor@space.svec.uh.edu

Our group focuses on vacuum based deposition techniques such as molecular beam and chemical beam epitaxy (MBE and CBE). These have several advantages over MOCVD, such as lower growth temperature, in situ control of the growth, integration with other material systems, and possibly lower infrastructure, maintenance and production costs. Not all of these advantages have been realized to date. A better fundamental understanding of the growth mechanisms and material properties is critical to making MBE techniques competitive with MOCVD.

Our research group has designed and built a molecular beam epitaxy (MBE) system for the growth of GaN and related thin films and heterostructures. The system consists of a cylindrical growth chamber with a gravity held 3" diameter sample holder. It uses solid sources for Al, Ga, In, Mg, and Si deposition, and a gaseous rf-plasma nitrogen source or ammonia for N species delivery. The manipulator allows for x-y-z motion and rotation of the sample during growth. Reflection high-energy electron diffraction (RHEED) characterization is available for thin film surface structure determination.

Based on our experience, control of GaN MBE growth is significantly more complicated than that of other "traditional" III-V semiconductors. This is due to higher growth temperatures (700-850°C), low surface mobility of group III elements on N terminated surfaces, necessity to keep unit flux ratio between group III elements and N during the growth, and the unavoidable use of substrates with large lattice mismatch.

Our current studies are focused on the growth of device quality materials on Si wafers using our experience with sapphire wafers, including the initial stage of heteroepitaxy, strain relaxation, and in situ control of the growth by low energy ion scattering recoil spectroscopy.

Various experiments, utilizing this growth chamber have been already conducted and are underway. Please, see our recent publications for details.

In situ control of the GaN -based materials growth by time of flight mass spectroscopy of recoiled ions

Task Leader: Dr. Esther Kim EstherK@space.svec.uh.edu

Secondary ion mass spectroscopy (SIMS) is the most widely used and sensitive ex situ ion-based technique for material composition analysis. Unfortunately, in its present state SIMS does not allow real time thin film characterization under process conditions.

Time of flight mass spectroscopy of recoiled ion (TOF MSRI), a technique developed by Ionwerks, overcomes SIMS imitations through detection of high energy recoils in a glancing geometry. The advantages of TOF MSRI are: Operation at pressures up to 1 mTorr, isotopic sensitivity to all elements including hydrogen, high sensitivity to nitrogen, and virtually non-destructive analysis.

The TOF- MSRI technique has been successfully integrated in our laboratory with a GaN growth reactor. The reactor permits both gas source molecular beam epitaxy (GSMBE) and chemical beam epitaxy (CBE) GaN deposition.

The combination of time-of-flight low energy ion scattering (TOF-ISS) and RHEED makes for a powerful and unique in-situ surface characterization tool. They have allowed us to study the influence of growth conditions on the thin film quality (crystallinity, surface roughness, structure, and true surface termination), impurity or elemental incorporation mechanisms and interlayer diffusion studies, and direct measurement of the surface III to V ratio.

Currently we are investigating selective area growth of III-N compounds on various buffer layers. Such studies are directed toward fundamental understanding of important issues such as: (I) epitaxial lateral overgrowth dependence on crystal structure, termination and vicinal surfaces; (II) selective epitaxy for field emission tip arrays.


Space Vacuum Epitaxy Center
Web Spinner: Dave Moore WebSpinner@SVEC.UH.edu

Last modified: 06 Sep 2001