Investigation of optical gain and L-I characteristics in (GaIn)(NAs)/GaAs lasers

Abstract

GaInNAs quantum well lasers have attracted significant interest in recent years. Their potential for operation at high temperatures without coolers and their application for low cost vertical-cavity surface-emitting lasers (VCSELs) are the main reasons for this interest. The main consequence of adding Nitrogen (N) to InGaAs materials is the band gap shrinkage. The reason for that is the interaction of N (acting as a localized defect) with the conduction band of the InGaAs. In previous studies, low temperature PL measurements of the impact of Nitrogen on the band structure of GaIn NAs have been examined. Pulsed measurements using a broad area GaInNAs QW laser were carried out and the results were analyzed in terms of the interaction of the N defect state with the GaInAs conduction band edge (band-anticrossing model). A detailed experimental temperature study of single quantum-well GaInNAs lasers at room temperature and above has been carried out. Experimental results of L-I, T₀, temperature dependence of lasing wavelength, optical gain and efficiencies are presented, discussed and compared with other materials. The temperature ranges studied is appropriate for most network applications. The gain spectra for moderate densities were experimentally measured using the method of Hakki and Paoli: the 600 μm long devise is biased below threshold and the gain is evaluated form the Fabry Perot modulation of the spontaneous emission spectra. A new concept will be introduced to study the bandwidth of the spectral gain and see its dependence with the temperature. The half-peak-BW will be the bandwidth where the gain decreases 50% from the peak gain. The temperature performance of the half-peak-BW has been studied obtaining a slope of 0.5871 nm/K. About the temperature dependence of the laser, a value of T_o (50 K) similar than the one found in InGaAsP has been found. This might disagree with the first results published of this new material system, giving extremely high values above 100 K. This is due to the high A parameter found in the previous materials. The improvement of the material is decreasing the A parameter and the characteristic temperature of the device. A small temperature dependence of the lasing wavelength was found (0.37 nm/K). This value was confirmed measuring the temperature dependence of the gain peak wavelength. This small temperature dependence can be understood by the interaction of the N state with the conduction band edge.