| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
U7, GaN1-xBix: Extremely Mismatched Alloys |
| Author(s) |
Alejandro X. Levander, Sergei V. Novikov, Zuzanna Liliental-Weber, Alex Tseng, Jonathan D. Denlinger, Oscar D. Dubon, Tom Foxon, Junqiao Wu, Wladek Walukiewicz, Kin-Man Yu |
| On-Site Speaker (Planned) |
Alejandro X. Levander |
| Abstract Scope |
Semiconductor alloying is a common method for tailoring material properties for specific applications. In the class of semiconductors known as highly mismatched alloys (HMAs) component atoms are partially substituted with isoelectronic elements with very different atomic radius and/or electronegativity. Here we present an extreme case of group III-V HMAs where nitrogen with electronegativity of 3.5 eV and atomic radius of 75 pm is partially replaced with bismuth, which has a much smaller electronegativity of 1.8 eV and much larger atomic radius of 155 pm. Films of GaN<SUB>1-x</SUB>Bi<SUB>x</SUB> alloys with x up to 0.11 were grown at the temperature of ~100°C on sapphire substrates using non-equilibrium low temperature molecular beam epitaxy (LT-MBE). The bismuth content increases monotonically with decreasing growth temperature. Although the dominant Bi-containing phase is amorphous however, due to the extreme anion mismatch. X-ray diffraction (XRD) shows a presence of a small number of GaN crystals, possibly distributed throughout the film. A dramatic reduction in the optical band gap from 3.4 eV in GaN to < 1.2 eV for x ~ 0.11 has been qualitatively explained by the formation of a narrow band originating from the band anticrossing (BAC) interaction between localized Bi states and the extended states of the GaN matrix. Lowering the growth temperature further to ~80°C and using the bismuth beam equivalent pressure to alter the Bi content, the GaN crystalline phase was eliminated from the XRD pattern and a completely amorphous GaN<SUB>1-x</SUB>Bi<SUB>x</SUB> alloy with Bi content of up to ~20-25% was achieved. A systematic study varying the Ga and Bi flux during growth revealed that a Ga-rich condition was necessary to grow GaN<SUB>1-x</SUB>Bi<SUB>x</SUB> alloys with III/V ratio = 1. We have also studied the electronic structure of GaN<SUB>1-x</SUB>Bi<SUB>x</SUB> using soft x-ray absorption and emission (XAS/SXE) to probe the valence and conduction band density of states and determine the position of the band edges. These experiments verify the interaction of localized states introduced by the extremely mismatched Bi atoms with the extended states of the host valence band states. The electronic and optical properties of GaN<SUB>1-x</SUB>Bi<SUB>x</SUB> will be correlated with the microstructure revealed by transmission electron microscopy studies. |
| Proceedings Inclusion? |
Undecided |