Ulf Olin

Ultrafast carrier trapping in Be-doped low-temperature-grown GaAs

Time-resolved photoluminescence is used to study low-temperature-grown (LTG) GaAs with Be doping. It is observed that the carrier trapping time in the as-grown LTG GaAs increases with Be doping. Similar effect is observed also in the annealed samples doped with less than 3×1019 cm−3 of Be. At higher doping levels, the trapping time in these samples is abruptly reduced to below 100 fs. This behavior is attributed to changes in As antisite density and the compensation effect of Be.

Optical bistability and gating in metalorganic vapor phase epitaxy grown GaAs étalons operating in reflection

Nonlinear Fabry–Perot etalons of GaAs have been fabricated with metalorganic vapor phase epitaxy technology. The etalons operate in reflection mode, and have an epitaxially grown, rear dielectric mirror consisting of a stack of alternating AlAs/GaAlAs layers. Optical logic functions using a HeNe laser and optical bistability at room temperature are reported. Low switching powers and improved etalon uniformity are obtained.

Subpicosecond carrier lifetimes in GaAs grown by molecular beam epitaxy at low substrate temperature

Time‐resolved photoluminescence transients of low‐temperature molecular beam epitaxially grown GaAs layers have been measured with femtosecond temporal resolution and compared with numerical Monte Carlo calculations. It has been shown that the shape of these transients measured at different emission energies is determined not only by the carrier lifetime but also by the electron redistribution in the conduction band. Analysis of the experimental results yields the carrier lifetime in the investigated samples of 400 fs.

Interwell carrier transport in InGaAsP multiple quantum well laser structures

We present direct measurements of interwell carrier transport in InGaAsP quantum well (QW) laser structures performed by time‐resolved photoluminescence. Conditions of originally empty and filled wells are explored. In both cases, the time for the hole transport across the structure is found to be of the order of tens of picoseconds. Comparison of experimental results and simulations allowed us to develop an adequate interwell carrier transport model that includes thermionic capture/emission over the QW interfaces and drift/diffusion in the barrier regions. We show that dynamic consideration of carrier densities and band bending for each QW are essential.

LOW-POWER OPTICAL BISTABILITY IN A THERMALLY STABLE ALGAAS ETALON

Optical bistability with 10 mW input power is reported in a thermally stable, nonlinear AlGaAs etalon. A 3‐μm‐thick silver layer, which serves both as high‐reflecting mirror and heat sink, makes it possible to operate the device at arbitrary duty cycles and pulse lengths up to 0.5 s, without any regenerative pulsations, at room temperature. The device operation depends on the plasma‐induced electronic nonlinearity, and switching times are typically 10 ns. Device performance is compared with results from a numerical model which takes diffraction, diffusion, and heat conduction into account.

Transverse effects in switching of bistable Fabry–Perot etalons filled with a saturable medium

A systematic variation of the Fresnel number has been performed when solving the nonlinear wave equation for a Fabry–Perot etalon filled with a saturable medium and including unsaturable background absorption. We show that the optimum Fresnel number for absorptive and defocusing bistability in media such as CdS, using the nonlinearity due to the bound exciton resonance, can be considerably greater than one and that bistability is completely lost for tight focusing.

Model for optical bistability in GaAs/AlGaAs Fabry–Perot étalons including diffraction, carrier diffusion, and heat conduction

A new model for optical bistability in layered semiconductor Fabry–Perot etalons is presented. The model accounts for diffraction, carrier diffusion, and thermal conduction. Assuming that the spot size and the thickness of the nonlinear layer are smaller than the diffusion length of the carriers, a simplified model is derived that has been used to design bistable AlGaAs etalons with improved thermal properties.

Photoexcited carrier transport in InGaAsP/InP quantum well laser structure

Measurements of photoexcited carrier transport in InGaAsP/InP graded‐gap separate‐confinement quantum well laser structures with a step‐like profile of the graded layers are performed by time‐resolved photoluminescence using upconversion. In all the investigated structures ambipolar carrier motion can be characterized by a constant velocity of (1.5±0.2)×106 cm/s. The experimental results are discussed in terms of step‐driven and ordinary diffusion.

Effects of diffraction and diffusion in dispersive optical bistability in Fabry–Perot étalons

Transverse effects in optical bistability, when both diffraction and diffusion are taken into account, have been studied. A numerical method is presented, as well as results for dispersive optical bistability in Fabry–Perot resonators for different diffusion lengths. It is shown that for small spot sizes, diffraction considerably influences the transmission characteristics and hysteresis disappears when diffusion is present.

Electron relaxation and capture in InGaAsP quantum well laser structures

Experimental investigations of electron relaxation in the confinement region and capture into the quantum wells are reported for InGaAsP/InP laser structures. The measurements are performed by time‐resolved photoluminescence using upconversion. The value for the electron capture of 1.4 ps is obtained. No dependence on the potential profile of confining layers has been observed.