Effects of plasma species during the molecular-beam epitaxy growth of dilute nitride semiconductors for infrared optoelectronic device applications

Dilute nitride semiconductors based on GaInNAs have a large range of infrared optoelectronic device applications. The incorporation of a small amount of nitrogen (~1-3% N) causes a significant wavelength redshift (~150meV-%-1) in the optical response, which has a variety of applications for the near- (1.06-1.55µm) to mid- (2-5µm) infrared. The molecular-beam epitaxy growth of narrow bandgap dilute nitrides most often requires a plasma source to incorporate nitrogen into InGaAs. There are however implications on the optical properties with this nitrogen incorporation, which are a result of defects due to the N atoms and the various plasma species required for the nitrogen incorporation. My work helps to further elucidate the impact of these effects; in particular, I focus on the effects of plasma species on the optical properties of dilute nitrides. To this end, GaInNAs-based quantized structures were grown by plasma-assisted molecular beam epitaxy in a Varian Gen 2 MBE system. Quantum well heterostructures, with AlAs cladding layers, were grown to mimic a device structure. An Applied-Epi UniBulb radiofrequency plasma source was used to activate nitrogen species from an N2/Ar source gas mixture. The plasma source was equipped with two parallel DC-biased ion deflector plates. Samples were grown on GaAs substrates under different plasma, ion, and growth conditions. Materials were characterized using x-ray diffraction and room temperature photoluminescence. The x-ray diffraction was primarily used to resolve structural compositions, whereas peak photoluminescence intensities were used to determine material quality. Both in situ and ex situ plasma diagnostic tools were used, which include optical emission spectrometry and a dual-grid retarding field ion energy analyzer, respectively. Samples were annealed by rapid thermal annealing to improve the optical response and to further study the effects of plasma species. A greater number of ions and higher ion energies demonstrated a deleterious effect on optical properties. It was found that both polarity and magnitude of the applied DC-bias are important considerations when choosing an appropriate deflector plate voltage. Furthermore, atomic nitrogen species may be more efficient in the nitrogen incorporation of dilute nitride materials, when compared to metastable nitrogen species of the N2 molecule.