Refractive index expressions for Ga 1 − x ln x As , GaAs 1 − x N x and Ga 1 − x ln x N y As 1 − y alloys

Dilute nitride alloys have attracted considerable interest in recent years because their potential for optoelectronic device applications. Particularly, GaInNAs/GaAs laser diodes (LDs) are one of the strongest candidates as alternative to GaInPAs/InP devices commonly used in telecommunication systems at 1.3-1.5μm. However, while GaInNAs/GaAs LDs at 1.3μm with low threshold currents and high values of characteristic temperature (T 0), have been obtained by several groups [1-3], there are still serious problems to experimentally achieve optical emission at 1.55 μm. Results indicate that to make real the full potential of dilute nitride LDs a further optimization of the structures is needed. For this purpose an accurate knowledge of materials parameters such as the refractive index is required. An exact knowledge of the refractive index is needed to properly design the laser waveguide. While for Ga1−xlnxAs, experimental data and expressions for the refractive index have been published [4-7], GaAs1−xNx and Ga1−xlnxNyAs1−y have been less studied. Due the lack of accurate data for Ga 1−xlnxNyAs1−y, values of the refractive index between 3.6 and 3.8 have been used in simulation of lasers structures emitting at lasing wavelength of 1.3μm [8,9], but there are some inconsistencies in the published data. For example Miloszewski et al [10] in simulation of MQW Ga0.62In0.38NyAs1−y laser structures used values of the refractive index of: 3.725, 3.722 and 3.712 ( y = 0.1, 0.5, 1.8), in contradiction with the experimental observation that the refractive index of Ga 1−xlnxNyAs1−y increases in proportion to the nitrogen content, as in others III-V alloys. Report by Kitataniet al [11], give Ga1−xlnxNyAs1−y refractive index data for samples with x = 33% and nitrogen compositions of 0.5% and 0.6%, obtained from spectroscopy ellipsometry (SE) in the wavelength range from 1.15 to 1.50μm. Their results shown that the refractive index increases as N concentration increases, according to the trend observed in conventional III-V semiconductor alloys in which a decrease in the band gap energy is accompanied by the increase of the refractive index. Leibiger et al [12] reported the refractive index of Ga1−xlnxNyAs1−y in the wavelength range from 0.95 to 1.65μm for five combinations of indium and nitrogen concentrations. Jinet al [13] reported values of the refractive index between 3.6 and 3.8 for a 1.3 μm Ga1−xlnxNyAs1−y MQW Fabry-Perot laser. The modal refractive index was obtained by measuring the longitudinal mode separation between two adjacent modes from the laser emission spectra. On the other hand Li et al [14] studied the refractive indices of Ga1−xlnxNyAs1−y in the wavelength range 400 < λ < 700 nm, which is below the range of interest for practical telecom lasers. Since the indium mole fraction used in the Ga1−xlnxNyAs1−y active layers of lasers diode is around of 0.36%, it is important to accurately know the refractive index for samples with this composition. MacKenzie et al, measured the amplified spontaneous emission spectra for a Ga0.613In0.387N0.012As0.988 QW edge emitting laser and extracted a refractive index value of 3.75 [15]. In this work, we carefully evaluates the available refractive index data and propose an expression suitable to estimate the refractive index of Ga 1−xlnxNyAs1−y alloys for the nitrogen composition and wavelengths range of interest, including the cases of Ga 1−xlnxAs, GaAs1−xNx alloys.