InAs self-assembled quantum dot and quantum dash lasers on InP for 1.55 μm optical telecommunications

1.3 mum quantum dot (QD) lasers grown on GaAs substrates have recently shown promising performances. For the 1.55 mum wavelength range, QD structures grown on InP substrates have been proposed to produce lasers for long haul telecom. At this wavelength, the progress has been delayed by the difficulties to obtain high density of small QDs by molecular beam epitaxy. On (100) InP substrates, elongated structure named quantum dash (QDH) are achieved in the standard conditions. The growth on high index substrates allows the achievement of a higher density of smaller quantum dots. In this paper, we compare laser performance of devices elaborated on both substrates. After quantum dot elaboration optimization, on (311) B substrates, laser emission at 1.59 mum on the ground state transition is obtained at room temperature (RT), A very low threshold current density (Jth) of 21 A/cm² for the best QD lasers is measured. This value can be compared to the Jth of quantum well (QW) laser, which are in the few hundred A/cm2. On (100) substrates laser emission is observed at 1.45 mum for a current density of 375 A/cm2 at RT. The evolution of the Jth and of the emission wavelength as a function of temperature is studied on both structures. The changes are interpreted in terms of density of states and of form of the gain curve