| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
U4, Highly Mismatched GaN1-xAsx Alloys across the Entire Composition Range |
| Author(s) |
Alejandro X. Levander, Sergei V. Novikov, Zuzanna Liliental-Weber, Iraida N. Demchenko, Jonathan D. Denlinger, Franziska Luckert, Robert W. Martin, Oscar D. Dubon, Tom Foxon, Junqiao Wu, Wladek Walukiewicz, Kin-Man Yu |
| On-Site Speaker (Planned) |
Alejandro X. Levander |
| Abstract Scope |
Typically only dilute (up to ~10%) highly mismatched alloys (HMAs) can be grown due to the large differences in atomic size and electronegativity of the host and the alloying elements. Recently, we overcame the miscibility gap of the GaN<SUB>1-x</SUB>As<SUB>x</SUB> system using low temperature molecular beam epitaxy (LT-MBE) and successfully synthesized alloys over a wide composition range. In the intermediate composition range (0.10 < x < 0.75) the resulting alloys are amorphous. Including the amorphous alloys, the band gap energy of the GaN<SUB>1-x</SUB>As<SUB>x</SUB> alloy spans from ~0.8 eV – 3.4 eV opening a wide range of possible applications, especially for multi-junction solar cells with a single semiconductor material system. It is important to note that the amorphous alloys have been grown on sapphire, silicon, and inexpensive glass substrates. Transmission electron microscopy (TEM) selected area diffraction (SAD) patterns and high resolution micrographs show that the alloys in the intermediate composition range are homogenously amorphous. The optical absorption spectra show very sharp absorption edges and a systematic shift of the absorption edge energy with composition indicating strong local ordering of the amorphous alloy. The band gap energy has also been confirmed by measurements of photomodulated reflectance, which probes the critical points of the density of states. We have also performed soft x-ray absorption and emission (XAS/SXE) measurements to probe the valence and conduction band density of states and determine the position of the band edges of GaN<SUB>1-x</SUB>As<SUB>x</SUB> with various As content. The thermal stability of these highly non-equilibrium alloys is important since device fabrication often requires high temperature processes. We have investigated the stability of these alloys in both furnace anneals and rapid thermal anneals (RTA). The a-GaN<SUB>1-x</SUB>As<SUB>x</SUB> films are stable in the amorphous phase for one hour anneals in temperatures up to 600°C. The films are also stable for 700°C-10sec RTAs, but above this temperature the alloy phase segregates into the constituent binary semiconductor phases. The resulting GaAs and GaN nanocrystals are uniformly distributed throughout the film and the relative size of the nanocrystals depends on the initial film composition and annealing conditions. The stability of the amorphous phase also suggests that the cations and anions in the as-grown a-GaNAs alloys are indeed randomly distributed. We will discuss our initial efforts to quantify the local structural order using extended x-ray absorption fine structure (EXAFS). |
| Proceedings Inclusion? |
Undecided |