Pros and cons of green InGaN laser on c‐plane GaN

Abstract

The challenges of green InGaN lasers are discussed concerning material quality as a function of InGaN composition, quantum well design and piezoelectrical fields. Investigations of polar quantum well designs and comparison with simulated nonpolar structures demonstrate that the quality of the indium rich layers is more important than the influence of interface charges. A high risk of dark spots at high In concentrations of 26-33% is observed. Small changes of about 2% of In significant reduce or increase the quantity and size of dark luminescence areas. Polar designs are a trade-off between low indium concentrations of 4 nm wide quantum wells and high overlap of electrons and holes in 2 nm narrow designs. Furthermore, our single quantum wells have less non-radiative defects than indium rich multiquantum well structures. Optimized active layer designs and the material qualities enable us to get green InGaN lasers on c-plane substrates for cw operation at 515-524 nm and wall plug efficiencies of 3.9-2.3%. Slope efficiency of 0.3-0.4 W/A allows up to now highest optical output power of 50 mW.

Influence of quantum well inhomogeneities on absorption, spontaneous emission, photoluminescence decay time, and lasing in polar InGaN quantum wells emitting in the blue-green spectral region

“…1(c). It is worth noting that also other authors reported that lasing from polar InGaN QWs is expected/observed when the electric field related to polarization effects is partially screened [14,32,33].…”

Critical impact of Ehrlich–Schwöbel barrier on GaN surface morphology during homoepitaxial growth

“…To accommodate the double bilayer structure of the wurtzite lattice along [0001], sites for only one sub-lattice on alternating bilayers are considered in the simulation (Fig. 2), this leads to a small offset in the simulation grids between the two types of bilayer along the [11][12][13][14][15][16][17][18][19][20] direction. The simulations were performed to deposit 1000 monolayers (MLs) of material onto the substrate, at rates of between 1 and 80 ML/s, and for both 400 x 400 and 800 x 800 site models with screw periodic boundary conditions.…”

“…Nucleation on the terrace of 2D islands without (c) and with (d) an ESB.Neighbors of atomic sites in the kinetic Monte Carlo simulations. The sub-lattices and six site neighbors for a site (larger circle) in each of the two bilayers, 1 and 2, are shown in red and physical sublattice is represented in the simulations, with a displacement of the hexagonal grid along ±[11][12][13][14][15][16][17][18][19][20] between each bilayer. flow growth mode without (a) and with (b) an ESB.…”

Challenges and approaches of fabricating GaN-based green lasers

“…A positive effect of built-in fields is however that it also reduces transition energy i.e. increases emission wavelength, which allows using less In concentration to achieve desired lasing wavelength [1]. But this benefit can only be useful if low optical gain is needed to reach threshold (Fig 1(a)), i.e.…”

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During recent years, several research groups have demonstrated a steady progress in increasing InGaN quantum well (QW) laser emission wavelength [1][2][3][4][5], however the threshold current ( Fig. 1) and wall plug efficiency (WPE) are still worse than those for blue LDs.

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