Current confinement and leakage currents in planar buried-ridge-structure laser diodes on n-substrate

An electrical device model for the planar buried-ridge-structure laser on n-type substrate is discussed. It takes into account the finite p-type contact resistivity, the two-dimensional current spreading, and the electron leakage current by drift and diffusion. Using this model, the influence of the relevant device parameters on the leakage current in InGaAsP/InP devices emitting at 1.3 μm is investigated. It is shown that leakage currents are negligible at room temperature if the contact stripe width does not exceed the sum of the active region width and the p-type confinement layer thickness, but they increase markedly with broader contact stripes and with contact resistivities above 10^-5 Ω-cm². The most important parameter influencing the leakage currents is the doping level of the P-InP confinement layer. With a p-type doping level of 1×10¹⁸ cm^-3, a p-type contact resistivity below 10^-5 Ω-cm² and a contact stripe width of 6 μm, the model calculations predict a maximum operation temperature exceeding 100°C. This agrees fairly well with experimental data proving that the rather simple planar buried-ridge-structure laser performs as well as more sophisticated devices incorporating current-blocking layers