| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Friday Sessions |
| Session TF-FrM |
| Session: | Thin Films: Growth and Characterization II |
| Presenter: | Michael Moseley, Georgia Institute of Technology |
| Authors: | M.W. Moseley, Georgia Institute of Technology B. Gunning, Georgia Institute of Technology J.E. Lowder, Georgia Institute of Technology G. Namkoong, Old Dominion University W.A. Doolittle, Georgia Institute of Technology |
| Correspondent: | Click to Email |
MME is a growth technique applied to molecular beam epitaxy of III-nitrides in which metal and dopant cell shutters are periodically opened and closed while active nitrogen flux remains constant. This technique uses metal-rich fluxes that would accumulate droplets in traditional MBE, taking advantage of the enhanced adatom mobility provided by excess metal. The periodic shuttering of the effusion cells allows the excess metal to be consumed, providing smooth, dry surfaces required for devices that demand abrupt interfaces.
In this study, MME is applied to the growth of InGaN and transient RHEED intensities are monitored for differing metal shutter open times (Fig. 1). It is found that these RHEED transients are the result of a RHEED oscillation associated with the buildup and consumption of the metal adlayer. This allows for observation and control of fractions of adsorbed metal layers. However, there is a drastic difference between the RHEED transients of low and high metal shutter open times. This difference is attributed to indium surface segregation, resulting in leftover In on the surface that does not form InN at these elevated temperatures. A model for adlayer buildup and consumption is developed, and a key RHEED signature is identified as the onset of surface segregation. The thickness of the adsorbed metal at this onset is found to be between 1 and 2 ML for various compositions. Samples grown throughout the miscibility gap using this technique exhibited single phase XRD spectra and < 1 nm RMS roughnesses (Fig. 2). High hole concentrations in p-InGaN are also achieved by MME (Fig. 3).
At the low temperatures required for high indium-content InGaN, an intermediate growth regime in MBE does not exist. Thus, traditional MBE cannot produce metal-rich InGaN without droplets or surface segregation. Because the onset of surface segregation (1<x<2 ML) occurs below droplet accumulation (<2.3 ML), this study confirms that for metal-rich InGaN growth, some form of modulation must be employed.
This work was supported by the Air Force Office of Scientific Research under a basic science grant managed by Kitt Reinhardt.