Critical Microscopic Processes in Semiconductor Lasers
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Abstract The cascade of microscopic processes relevant to semiconductor laser operation is outlined. An integrated laser simulator which encapsulates these processes is applied to illustrate the connection between an accurate model of the optical gain in the quantum wells and measured characteristics of representative 1.3 ýtm InGaAsP/InP lasers. These results highlight the impact of carrier transport effects on the observed optical gain and the modulation response of semiconductor lasers.
Introduction The optical gain obtained by injection of electrons and holes into a semiconductor is fundamental to the operation of a semiconductor laser diode. Theoretical treatment of the optical gain is a challenging, many-body physics problem. However, the systematic comparison of any theoretical analysis of gain to experiments presents substantial additional problems. From the theoretical perspective, it is natural to treat the optical gain of a region of the device (e.g. a quantum well) as a function of the local density of electrons and holes. However, measurements of the optical gain must be performed with either optical or electrical excitation of this region. The bias conditions of the device or material may be accurately known, but the actual carrier accumulation in the region of interest (i.e. a quantum well) is the consequence of a generally complex sequence of transport and recombination processes. This renders direct and reliable comparison between theory and experiment difficult. More broadly, the transport and recombination processes are quite important to understanding and optimizing the performance of the laser diode. Substantial theoretical effort has been devoted to the important processes in semiconductor lasers e.g. optical gain, non-radiative recombination, carrier scattering, etc [1]. However it has also been recognized that an integrated approach is essential. Recent work incorporates bulk carrier transport, carrier capture into quantum wells, the optical gain in the quantum wells and the stimulated emission process [2-6]. This allows direct contact with measured laser diode characteristics. Unfortunately, it also increases the number of physical models that must be independently verified. A much broader base of experimental data is required to establish the accuracy of the simulations. More comprehensive comparison to experimental data supports a critical analysis of the essential microscopic processes. In this paper, we give a brief overview of the microscopic processes required to understand multiple quantum well semiconductor lasers. We discuss the incorporation of each process into an integrated simulator which has been described in more detail elsewhere [5-7]. We then conclude with a comparison of simulated and measured gain spectra for a typical InGaAsP/InP based 1.3 ptm laser designed for telecommunications applications. We show the impact of the transport processes on the modulation response of the laser.
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Mat. Res. Soc. Symp. Proc. Vol. 579 © 2000 Materials Research Society
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