| The GaInNAs(Sb) material system provides a promising solution for realizing low-cost optoelectronic devices operating in the wavelength range of 1300--1600 nm. Such devices are important for addressing current bottlenecks in optical fiber communication networks and for enabling optical interconnect technology to replace electrical lines limiting the future speed of microelectronics.; A unique property of this material system is that the incorporation of small concentrations of N (<2 at%) sharply lowers the band gap. Also, the luminescent efficiency of as-grown material is generally poor, but can be improved 20--100x by annealing. The increased luminescence, however, is accompanied by an undesirable blueshift of the band gap by 50--150 nm, which is unacceptable for reproducible control of the operating wavelength of devices. First principles band structure calculations are used to explain the band gap lowering in terms of the nature of N-related band-edge states. Using a combination of theoretical calculations and x-ray absorption, electroreflectance, photoluminescence, and photocurrent spectroscopies, the band gap shift after annealing is found to be caused by a thermodynamically-driven reconfiguration of N nearest neighbors, from mostly N-Ga as-grown to mostly N-In, which corresponds to a larger band gap state. Many properties of this material system are dominated by the semi-localized N band-edge states.; The electroabsorption properties of GaInNAs(Sb) quantum wells (QWs) are examined with photocurrent spectroscopy to determine their applicability for optical modulators. Excellent quantum confined Stark effect behavior is demonstrated, with sharp excitonic resonances. The peak absorption coefficient of fully annealed GaInNAsSb QWs is measured to be ∼35,000 cm-1 at 1525 nm wavelength, while annealed GaInNAs QWs exhibit peak absorption of ∼8,000 cm-1 at 1250 nm. In addition, thermal annealing was found to increase the absorption coefficient ∼2x, through enhancement of the oscillator strength by the atomic reconfiguration described above. The measured electroabsorption characteristics indicate that optical modulators can be fabricated throughout the 1300--1600 nm wavelength range with performance comparable or superior to{09}current technology. A modulation ratio of up to 15--20 dB over a 15--20 nm optical bandwidth using less than a 3 V swing is predicted for an asymmetric Fabry-Perot reflection modulator. |
