The tunnel injection structure idea is to place an auxiliary quantum well (QWell) in the vicinity of quantum dot (QDot) area, separated with a thin barrier only. QWell serves as a reservoir of carriers, which next tunnel laterally into the QDot states. In such a system several fundamental laser parameters can be improved: carrier collection, threshold current and modulation rate.

There is presented an optical characterization of tunnel injection structures designed for 1.55 μm laser emission. The structures are based on InP substrate with InAs quantum dashes (QDashes – elongated QDots) as an active area and InGaAs QWell as a carrier collector. There have been applied different optical spectroscopy techniques for full characterization of tunnel injection structures properties. Photoluminescence (PL) has been used to follow QDash and QWell ground state emission, photoreflectance (PR – highly sensitive absorption-like modulation technique) has given an information about energies of optical transitions in the whole structure and photoluminescence excitation (PLE) has allowed to probe directly the energy transfer from QWell to QDash ground state.

PL temperature dependence has revealed two recombination channels: through quantum well and via quantum dash ground states [1]. The strong relative QDash emission has been observed up to approximately 100 K. At higher temperatures the QDash emission decreases significantly in favor of QWell radiative recombination. Low temperature PLE experiment combined with PR measurements has proved the presence of the QWell-QDash ground state energy transfer [2]. The PLE temperature dependence has indicated the carrier transfer presence up to temperatures above 100 K.

[1] P. Podemski, R. Kudrawiec, J. Misiewicz, A. Somers, J. P. Reithmaier, A. Forchel, Appl. Phys. Lett. 89, 061902 (2006).
[2] G. Sek, P. Poloczek, P. Podemski, R. Kudrawiec, J. Misiewicz, A. Somers, S. Hein, S. Hofling, A. Forchel, Appl. Phys. Lett. 90, 081915 (2007).

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