Carsten Agert

(GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser with ultrabroad temperature operation range

The temperature dependence of the emission of a (GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser is investigated. We find laser emission over an extremely broad temperature range from 30 K up to 388 K. The laser threshold varies from 5 kW/cm2 at 373 K down to a minimum of 1 kW/cm2 at 180 K and increases again to 4 kW/cm2 at 30 K. Picosecond emission dynamics after femtosecond optical excitation is obtained with peak delays below 33 ps and pulse widths below 20 ps over the entire operation range.

Advanced III–V solar cell structures grown by MOVPE

Abstract The paper reports on the progress of MOVPE-grown III–V epitaxial structures and tandem solar cell development. A multi-wafer reactor with a capacity of five 4-in wafers is used to grow high-efficiency, large-area tandem solar cells. The benefits of advanced tandem structures for concentrator applications based on Ga0.35In0.65P/Ga0.83In0.17As grown lattice mismatched to GaAs are discussed. In order to achieve super-high efficiencies a mechanical stack of monolithic tandem cells made from Ga0.51In0.49P/GaAs and Al0.25Ga0.75As0.02Sb0.98/GaSb is suggested.

Completely passive operation of vapor-fed direct methanol fuel cells for portable applications

A vapor-fed DMFC with completely passive operation on both anode and cathode sides was demonstrated and employed for the research of structural parameters and operation under ambient conditions. By applying reference electrodes which were screen-printed on the same ionomer membrane with the working electrodes the potential losses on each side were evaluated separately. Thus, the reason for the losses could be discovered in detail. Comparisons between the air-breathing cathode and the forced air flow cathode between vapor methanol and liquid methanol feed were made with different methanol concentrations. It was found that the water profile on the electrodes, either produced from reaction or from the feed solution, could influence the cell performance dramatically. The different efficiencies of the vapor-fed DMFC were calculated. Due to the methanol crossover the total system efficiency was still very low for the vapor-fed DMFC. However, the fact that the cathodic potential loss for the vapor-fed DMFC in a high current density range is less than that for the liquid DMFC makes the former more attractive than the latter.

MOVPE of GaSb, (AlGa)Sb and (AlGa)(AsSb) in a multiwafer planetary reactor

Abstract Trimethylaluminum, tritertiarybutylaluminum (TTBAl) and dimethylethylamine alane (DMEAA) are compared as aluminum precursors for the growth of (AlGa)Sb and (AlGa)(AsSb) in an industrial size multiwafer planetary MOVPE reactor. The thermal activation behavior of the aluminum precursors is shown to be a critical factor as the growth is in the kinetically controlled regime. Both the efficiencies of TTBAl and DMEAA are shown to depend on the V/III-ratio which is attributed to prereactions with trimethylantimony. Oxygen and carbon concentrations are reported for various compositions of (AlGa)Sb. Compared to TTBAl, the use of DMEAA results in an oxygen level in (Al 0.19 Ga 0.81 )Sb which is reduced by approximately one order of magnitude.

Low oxygen content trimethylaluminium and trimethylindium for MOVPE of light emitting devices

The reduction in oxygen contamination levels in organometallic precursors has been established as a key requirement in the metal organic vapour-phase epitaxy (MOVPE) of high brightness light emitting diode (LED) and laser devices. A number of different volatile oxygen-containing impurity species have been identified, and both physical and chemical techniques have been developed to eliminate them from a wide range of source materials to produce the next generation grade of high-purity products. In this study conclusive growth results are presented to highlight the significantly improved quality of device structures obtained when higher purity oxygen-free precursors are employed.