Erbium doped III-Nitride semiconductors: Material synthesizing and applications

This thesis targets the development of erbium (Er) doped III-nitride materials that will permit the realization of compact and robust optoelectronic devices for optical communications (λ ~ 1.5 μm). The intra-4f transition of trivalent Er ions (Er3+) from the first excited to ground state (4I13/2→ 4I15/2) gives the 1.54 μm emission corresponding to the minimal optical loss window of silica fibers. The thermal and structural stability of wide bandgap III-nitride semiconductors encourage the use of III-nitride semiconductors as host materials for Er doping. The unique properties of Er doped III-nitrides open up opportunities to develop electrically pumped optical amplifiers that have the advantages of both and semiconductor optical amplifiers (small size and ability for optical integration) and erbium doped fiber amplifiers (minimal interchannel crosstalk in WDM networks). It may lead to integration with other functional optical devices including wavelength routers, optical switches, and detectors. This prospect becomes especially attractive if crystalline Er-doped III-nitride materials could be grown on Si (001) substrates making this material system truly compatible with standard processes of the CMOS technology for silicon photonic integration. In this thesis work, Er doped III-nitride materials were synthesized by metal-organic chemical vapor deposition (MOCVD) with in-situ Er doping. We investigated MOCVD growth conditions to promote the 1.54 μm emission of Er doped III-nitride semiconductors. With strain engineering using the heterostructural GaN:Er growth, photoluminescence (PL) emission at λ = 1.54 μm was observed to increase with the built-in bi-axial strain of GaN:Er materials; With an increase of GaN:Er growth pressure, the number of Ga vacancies decreased, which led to an enhancement in the 1.54 μm emission in current injected GaN:Er p-i-n emitters; By decreasing the NH3 flow rate used during GaN:Er growth, the excitation cross-sections of a GaN:Er epilayer were increased, which enhanced the 1.54 μm emission. Also, the growth of crystalline Er doped III-nitride epilayers on Si (001) substrates has been demonstrated using selective area grown GaN/AlN/Si (001) templates. This thesis also studies the possible excitation approaches to enhance the 1.54 μm emission of Er doped III-nitride semiconductors. The optical excitation cross-section of GaN:Er semiconductors was found to decrease with an increase of the excitation wavelength, which correlates well with the absorption coefficients of GaN host materials. On the other hand, the electrical excitation cross-section of GaN:Er was found to be roughly three orders of magnitude larger than the one using a resonant excitation with λexc = 980 nm or 1480 nm. This large electrical excitation cross-section makes Er doped III-nitride semiconductor a promising candidate for chip-scale optoelectronic devices. Moreover, the crystalline qualities of GaN:Er semiconductors were found to influence the optical attenuation of GaN:Er-based optical waveguides at λ = 1.54 μm. Experimental results revealed that only those GaN:Er epilayers with high crystalline quality (with a typical rocking curve linewidth of (002) x-ray diffraction peak ≤ 380 arcsec) are suitable for the practical applications as optical amplifiers. We have also achieved SiO2/TiO2 distributed Bragg reflectors with a reflectivity > 95% at λ = 1.54 μm prepared by e-beam evaporator. GaN:Er combined with SiO2/TiO2 DBRs may offer novel applications of Er doped III-nitride semiconductors including high power infrared lasers.