Combined effect of carrier heating and carrier transport on the intensity modulation response of quantum well lasers

Abstract

A model is proposed for high-speed modulation dynamics of quantum well (QW) lasers which includes the effects of hot carriers, hot phonons, carrier transport across a separate confinement heterostructure, carrier capture into QW and carrier emission from QW. It is shown that an effective potential barrier height and the carrier density in QW can be critical factors for the direct modulation performance of high-speed QW lasers. In the case of large carrier density and high degree of the confinement of phonon modes, there exists a threshold effective barrier height for rapid decrease in the modulation bandwidth. The microscopic origin of this dynamic behaviour of QW lasers is attributed to a multiplicative effect of carrier heating and carrier transport. At high modulation frequencies, in addition to the multiplicative effect, carrier injection heating influences strongly on the intensity modulation response resulting in increase of the modulation bandwidth under large band-gap offsets. Simple expressions for a time constant for electron temperature relaxation and a phonon number modulation factor are derived. It is demonstrated that these quantities depend strongly on the carrier density and the degree of the confinement of phonon modes.