CARRIER-DENSITY-INDEPENDENT RADIATIVE CONSTANT IN 1.3 MU-M BURIED HETEROSTRUCTURE LASERS

An important carrier dependence of the radiative coefficient in InGaAsP active material in semiconductor lasers which operate at wavelength 1.3 mu m is a result that has appeared in the literature for more than a decade. Quantitative measurements of the radiative current in 1.3 mu m buried heterostructure lasers with very low leakage characteristics are presented. These data show that the saturation of spontaneous emission versus current curves is caused by the large, voltage-dependent nonradiative component of the current, rather than by a ''shrinking'' radiative coefficient B. Moreover, the dependence of the radiative current on active-layer voltage V-j is well explained by the bimolecular law S proportional to Bnp, where S is the radiative current and n (p) is the electron (hole) concentration. Plots of log(S) vs V-j reflect both the Fermi statistics of the conduction-band occupation and motion in energy of the hole Fermi level. A carrier dependence of the radiative coefficient of the size reported in the literature cannot be reconciled with the fundamental attributes of the spontaneous emission data. The carrier dependence of B in the literature arises experimentally as a requirement of self-consistency between differential carrier lifetime and spontaneous emission versus current data. It is observed here that the carrier lifetime versus current curves, as measured, are distorted by the high impedance of the laser chip at low bias. If a correction to the lifetime data is made, consistency between lifetime and spontaneous emission data is achieved, with no need to invoke a carrier dependence of B. Furthermore, the nonradiative coefficient needed to fit the corrected lifetime data is three times larger than before. (C) 1995 American Institute of Physics.