Microwave circuit model of the three-port transistor laser

Based on an earlier charge control analysis, we have constructed a microwave circuit model of a three-port quantum-well (QW) transistor laser (TL) by extending Kirchhoff’s law to include electron-photon interaction, to yield an electrical-optical form of Kirchhoff’s law. The TL circuit model includes both intrinsic device elements and extrinsic parasitic elements, and fits accurately measured microwave $S$-parameters upto 20 GHz and matches also measured eye-diagram data up to 13 Gb/s (equipment-limited). The TL model yields both electrical and optical device parameters as well as physical quantities such as QW charge density, $nQW∼1016cm−3$⁠, which is useful in the analysis of the device physics of TL operation. The low density indicates that the base QW charge level is not as important as the current driving the QW and supplying electron-hole recombination, and implies that the quasi-Fermi level is discontinuous in the TL base. The model is used to simulate a directly modulated TL up to 40 Gb/s, for example, a TL employed in an optical communication link.