Hybrid Quantum Well/Quantum Dot Structure for Broad Spectral Bandwidth Emitters

We report a hybrid quantum well (QW)/quantum dot active element for an application in broadband sources. These structures consist of an InGaAs QW and six InAs dot-in-well (DWELL) layers. The single QW is designed to emit at a wavelength coincident with the second excited state of the quantum dot. We compare two hybrid QW/quantum dot samples where the QW position is changed, and show that carrier transport effects make QW placement very important through current-voltage, capacitance-voltage, photocurrent, and temperature-dependent spontaneous emission measurements. Using the optimal structure, due to the combined effects of quantum dot ground states, first excited state, and QW emission, a positive modal gain spanning ~300 nm is achieved for the segmented contact device. The values for modal gain are further confirmed by simultaneous three-state lasing, which is studied spectroscopically. Finally, a hybrid QW/quantum dot superluminescent diode (SLD) is reported; the device exhibits a 3 dB emission spectrum of 213 nm, centered at 1230 nm with a corresponding output power of 1.1 mW. The hybrid SLD is then assessed for an application in an optical coherence tomography system; an axial resolution of ~4 μm is predicted.