  The influence of the growth conditions as well as the device design on the
device performance of (GaIn)As/Ga(AsSb)/(GaIn)As "W"-quantum well lasers is
investigated. To this purpose, the epitaxy process is scaled to full two inch
substrates for improved homogeneity while the growth process is carried out in
a single run for an improved quality. Furthermore, the optical confinement
factor is increased by increasing the aluminum concentration within the
cladding layers to a value of 65%. The procedure is carried out for devices
with emission wavelengths of 1.26 micrometer as well as 1.30 micrometer.
Differential efficiencies as high as 58% and threshold current densities as low
as 0.16 kA/cm^2 are observed in case of devices emitting at 1.26 micrometer at
room temperature. Furthermore, excellent characteristic temperatures of T_0=(72
plus minus 5)K and T_1=(293 plus minus 16) K are recorded in the temperature
range between 10 degree Celsius and 100 degree Celsius. Devices emitting at
1.30 micrometer exhibit differential efficiencies of 31% and threshold current
densities of 0.50 kA/cm^2 at room temperature. Further improvements of these
properties and wavelength extension schemes are briefly discssused.
