AlGaAs Laser Diode

The SiLENSe software initially developed for III-nitride wurtzite semiconductors is adapted now to cubic III–V compounds. Database of materials properties was also updated to include optical characteristics of cubic III–V compounds.

This section illustrates software capabilities for simulation of 808 nm AlGaAs-based high-power laser diode.

Generally, to increase the differential quantum efficiency of a laser diode, one should reduce internal optical losses of the waveguide mode that first reaches the oscillation threshold. An effective way to reduce the internal optical losses is the use of a graded-index (GRIN) waveguide, producing a built-in pulling field due to the bandgap variation in the graded-composition material.

To illustrate this effect, we consider here the laser heterostructure specified as:

• 0.3 μm n-GaAs buffer layer (n = 2x10¹⁸ cm⁻³)
• 1.5μm n-Al_0.6Ga_0.4As cladding layer (n = 1x10¹⁷ cm⁻³)
• undoped 0.15 μm AlGaAs waveguide layer with the AlAs molar fraction descending from 0.6 to 0.3
• 10 nm strained InGaAlAs active region providing the light emission at 808 nm
• undoped 0.15 μm AlGaAs waveguide layer with the AlAs molar fraction ascending from 0.3 to 0.6
• 1.5 μm p-Al_0.6Ga_0.4As cladding layer (p = 2x10¹⁷ cm⁻³)
• 0.2 μm p+-GaAs contact layer (p = 1x10¹⁹ cm⁻³)

The background hole concentration in the nominally undoped waveguide layers is considered about 0.7 – 3.0x10¹⁶ cm⁻³, according to capacitance–voltage measurements.

Some computations results is presented on the Figs 1 -2. A specific feature of the band diagrams is a non-monotonic profile of the conduction band edge. This is due to the crossover of the Γ- and X-valleys resulting in variation of conduction band offset between GaAs and AlGaAs. Fig.3 and 4 present a comparison of theoretical predictions for some of the laser characteristics with observations. A good agreement between the theory and experiment justifies the applied approach and the main conclusions made on the basis of simulations.

Figure 3 The threshold current density as a function of the cavity length.

Figure 4 Predicted and measured threshold current and operation current corresponding to the output power of 2 W.

You can find more detailes in publication by K. A. Bulashevich, V. F. Mymrin, S. Yu. Karpov, D. M. Demidov and A. L. Ter-Martirosyan “Effect of free-carrier absorption on performance of 808 nm AlGaAs-based high-power laser diodes” Semicond. Sci. Technol. 22 (2007) 502–510