Gain Measurement of Highly Stacked InGaAs Quantum Dot Laser with Hakki–Paoli Method

Abstract

A 147-µm-long cavity laser diode with 19 InGaAs quantum dot layers was fabricated by the ultrahigh-rate molecular beam epitaxial growth technique, and its gain properties were investigated using the Hakki–Paoli method below the threshold current (Ith) of 111.5 mA. At an injection current of 100.3 mA (0.9Ith), the positive net modal gain was in the range between 1005 and 1043 nm, corresponding to a photon energy of 45 meV. The maximum net modal gain and maximum modal gain were 46.5 and 60.5 cm-1, respectively. A differential net modal gain of as high as 3.8 cm-1/mA was observed at 0.77 times the threshold current. No gain saturation appeared below the threshold current, and injection currents higher than 78.4 mA (≈0.7Ith) were required to obtain a net modal gain.