Electronic structure and optical properties of 1.55 µm emitting InAs/InGaAsP quantum dash tunnel injection structures
Optical spectroscopy studies have been reported on an application-relevant system emitting at 1.55 µm and consisting of an InGaAsP injector quantum well (QW), separated by a thin InP barrier (of various thicknesses) from InAs elongated quantum dots called quantum dashes (QDash). The investigated systems constitute tunnel injection structures, whose operation principle is the transfer of carriers captured by the injector QW to the QDash layer by means of tunnelling. Numerical calculations in the eight-band kp model with a realistic dash geometry are used in order to determine the energies of confined levels and their wave functions, results of which are then verified by comparison with measured photoreflectance spectra and used to interpret spectroscopic findings. The tunnelling of carriers from QW to QDash layer is evidenced by photoluminescence excitation measurements and further supported by unusual temperature behaviour of PL peaks broadenings. Careful numerical analysis of confined states and their wave functions explains optical properties of investigated samples. The suggestions for the proper design of structures based on the injection of carriers for applications in telecom lasers are given; most importantly it is shown that care must be taken so that the QW does not significantly influence the dash emitter.