In this paper we report on the multi-section gain and absorption analysis of strain engineered molecular beam epitaxy
(MBE) grown GaAs and InGaAs capped bilayers. The InGaAs capped bilayer quantum dot (QD) lasers extends the
room temperature lasing wavelength to 1.45 μm. The spectral measurement of gain demonstrates that net modal gain is
achieved beyond 1.5 μm at room temperature. Analysis of the temperature and current density dependence gain
characteristics of a GaAs capped bilayer sample indicate that the temperature sensitivity of threshold current around
room temperature is due to phonon assisted thermal escape of carriers from the QDs.
Quantum Dot lasers exhibit the novel phenomenon of dual state lasing where population inversion can be achieved on
two optical transitions within the dots. In principle this might occur if a phonon bottleneck exists to impede relaxation of
carriers from the higher energy state. Here we present an alternative explanation whereby different lasing modes
compete for carriers and are spatially separable. Evidence comes from a comparison of electrical and optical
measurements made on the devices. The evolution of a particular lasing mode depends on diffusion of carriers between
dots and we show how, using an equivalent circuit model, this is consistent with our measurements.
Self-assembled Quantum Dots (QDs)have great potential as the active region in semiconductor laser diodes, resonant cavity light emitting diodes and semiconductor optical amplifiers. Yet, after nearly a decade of intense research many of the promised advantages have yet to be fully achieved. In this paper it will be shown that this non-ideal behavior is the result of an inability to control the size, shape and composition of the three dimensional islands during growth and factors such as carrier relaxation, which are fundamental to the lasing process, are not well udnerstood. In addition, the presence of the wetting layer and non-radiative recombination centers incorporated in the barrier material during growth at temperatures below that normally used for high quality material lead to poor performance at high temperatures. The emphasis has recently shifted towards GaAs-based devices operating at telecomms wavelengths where there is the possibility of replacing InP-based emitters and fabricating vertical cavity lasers in the 1.3 and 1.55-micron wavelength regions. The progress here has been steady and it is likely that commercial products will be available soon. There are also encouraging indicators for single photon emitters utilizing single dots and wideband semiconductor optical amplifiers.
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