Microscopic Nonequilibrium Simulations in Semiconductor Laser Structures

In recent years, vertical cavity surface emitting lasers (VCSEL) have developed into an important semiconductor laser source in multiple applications. However, the limited output power of VCSEL systems restrains industrial applications. The vertical external cavity surface emitting laser (VECSEL) design overcomes this limitation by replacing the upper distributed bragg reflector by an external parabolic mirror. Nevertheless, heating of the active region and related phenomena as e.g. the thermal rollover arise and turn out to be the major problem for further enhancement of VECSEL output power (Zakharian et al., 2003). Those phenomena contain new challenges for the theoretical description. With our model, we have the unique possibility to simulate optical and thermal properties of VECSEL devices. An example shows the laser output spectrum of a VECSEL device experimentally measured with a streak camera setup. The VECSEL is pumped with a strong 500ns pump pulse. One clearly sees the thermal shift of the band gap corresponding to a lattice heating of 4.2K/mus. In comparison, our simulation shows a good agreement with a slope of the thermal heating of 3.6K/ mus for the same structure. Additionally, thermal resistance dependent rollover curves were calculated for the same structure and exhibit the expected behaviour. In the future we expect our simulations to aid in the design and manufacturing process of semiconductor lasers. On the more fundamental level, we are interested in the dynamics of the optical properties in connection to nonequilibrium carrier populations as present e.g. in chirped excitation.