Wolfgang Stolz

Ultrafast characterization of semiconductor gain and absorber devices for mode-locked VECSELs

We present a comprehensive characterization of semiconductor gain and absorber devices utilizing novel measurement techniques. Using a 20fs probe laser, a time resolution in the few femtosecond range is achieved in traditional pump and probe measurements performed on VECSELs and SESAMs. In-situ characterizations of VECSEL samples mode-locked in the sub-500fs regime reveal the fast and longtime recoveries of the gain present in real lasing conditions. Spectrally-resolved probing gives further information about the properties of carriers in VECSEL gain media. Our results indicate that stable mode-locked operation is sustained by multiple carrier relaxation mechanisms ranging from a few femtoseconds to the pico- and nanosecond regimes.

Growth of III/Vs on Silicon

The growth of III/V semiconductors on Silicon substrates has attracted great attention since quite some time as several promising device concepts rely on the defect-free integration of optically or electrically active III/V layers on Silicon substrates. The present chapter summarizes our present knowledge on III/Vs on Silicon growth with great emphasis on the defects, which can arise at the III/V-Silicon interface. We address (nearly) lattice matched growth of GaP or multinary III/Vs on Silicon as well as highly-mismatched growth of pure III-Nitrides and III-Arsenides as well as III-Antimonides on Silicon substrates. Throughout the chapter we highlight, how an understanding of growth mechanisms can lead to a minimization of defect density, making the layers suitable for device applications. Suitable characterization techniques to assess layer quality are also introduced in the text.

Solar Cell Characterization with High Spatial Resolution

New techniques for a solar cell characterization with high spatial resolution are introduced and evaluated both by experiments on test structures and numerical simulations. The reliability is demonstrated and technical limits are assessed.

Emission dynamics of (GaIn)(NAs)/GaAs lasers emitting at 1.3 μm

The emission dynamics of an optically pumped 1.3 +m (GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser is investigated. We achieve room-temperature operation at 1285 nm with a low optical pumping threshold and fast emission dynamics: A minimum peak delay of 15.5 ps and a minimum pulse width of 10.5 ps are observed after excitation with 100 fs pulses. Laser operation with picosecond emission dynamics is demonstrated over a wide temperature range from 30 K to 388 K. We explain this extraordinarily large temperature operation range on the basis of measurements of the optical gain in (GaIn)(NAs)/GaAs. We find a gain broadening at elevated carrier densities due to contributions of higher subband transitions.