InAs quantum dots, grown on GaAs, are a promising candidate for 1.3µm lasers for use in silica optical fibre-based local and metro data communications systems. In this application, lasers are sought to operate in road-side cabinets over a wide temperature range without the need for expensive temperature control. Key to the reduction of temperature sensitivity in QD lasers is the improving of energy level separation.
PL spectra taken at low and high powers enables the identification of the confined states of the quantum dot and the surrounding wetting layer, providing valuable information on the internal electronic structure such as energy spacing and confinement potential depth.
A 532nm DPSS laser is used to excite a cryogenically-cooled QD sample. The resulting photoluminescence was analysed by a Bentham DMc150 double monochromator and InGaAs photodiode, providing excellent stray light rejection and high sensitivity, to enable the resolution of weak features even at very high excitation levels of MW/cm2.
At low power, the ground state dominates, whereas at high excitation power, the ground, 1st, 2nd, 3rd and wetting layer are clearly seen. (Images and application information courtesy of Dr David Childs, University of Sheffield)