Based on recent improvements of growth of In-rich InGaN quantum wells with low defect density, we demonstrate current driven InGaN laser diodes at wavelengths as long as 500 nm. The laser structures are grown on c-plane GaN substrate and are processed as broad oxide-insulated stripe laser diodes. We discuss the impact of the piezoelectric field on the emission energy of long wavelength laser diodes for this growth orientation. The combination of low threshold current density of 8.2 kA/cm2 with high slope efficiency of 650 mW/A enables high output powers up to several tens of milliwatts.
In this paper we investigate the waveguiding (WG) of direct green InGaN laser diodes grown on c-planeGaNsubstrates. The problem of parasitic modes emerges due to the reduced refractive index difference between the GaN waveguide and AlGaN cladding layers for green compared to blue emitting laser diodes. We discuss several approaches to avoid substrate modes. We investigate different materials and designs for optimized WG of green InGaN laser diodes using a 1D transfer matrix simulation tool
We investigate the spectral properties of violet 405 nm (Al,In)GaN laser diodes (LDs). Depending on the substrate the LDs are grown on, the lasing spectra show significant differences. LDs grown on low dislocation GaN substrate have a broad spectrum with several longitudinal modes, while LDs grown on SiC substrate are lasing on a single longitudinal mode.With increasing current, the laser emission of LDs grown on SiC substrate jumps from one longitudinal mode to another (mode hopping), whereas GaN substrate LDs show a smooth but asymmetric mode comb. The different envelopes of these spectra can be understood by assuming a variation of the gain for each individual longitudinal mode. With a high spectral resolution setup, we measure the gain of each longitudinal mode, employing the Hakki-Paoli method. Measurements show a slightly fluctuating gain for the modes of GaN substrate LDs, but much larger fluctuations for LDs on SiC substrate. We carry out simulations of the longitudinal mode spectrum of (Al,In)GaN laser diodes using a rate equation model with nonlinear gain (self saturation, symmetric and asymmetric cross saturation) and including gain fluctuations. With a set of parameters which is largely identical for LDs on either substrate, the simulated spectra truly resemble those typical for LDs on GaN or SiC substrate.
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