Coupled quantum well to quantum dot heterostructure laser.

摘要

Quantum-dot (QD) active layers have received much attention because of the possibility of changing the step-density of states of a quantum well (QW, thin layer L_z $\lesssim$ 500 Å) to the discrete states of a QD (small “box” L_x, L_y, L_z $\lesssim$ 500 Å), potentially leading to an ultimate form of laser. However, significant inferior properties relative to the QW, such as carrier collection and redistribution properties, assure that the QW cannot be completely displaced by the QD. A new heterostructure system that combines the comparative advantages of the QW and the QD is proposed leading to the development of the coupled QW to QD heterostructure laser.; Data are presented demonstrating continuous 300-K photopumped InP quantum dot (QD) laser operation (656–679 nm) realized by coupling, via tunneling, an auxiliary InGaP QW to the QDs of an InP-In(AlGa)P-InAlP heterostructure.; Data are presented showing that a QD+QW laser diode has a steeper I-V characteristic than does a similar diode with no auxiliary QW. The InP+InGaP QD+QW diode is capable of 300-K visible-spectrum QD laser operation, while the single-layer InP QD diode (single QD layer) saturates at low current ($\lesssim$1 mA) and does not exhibit stimulated emission.; Data are presented demonstrating the cw 300-K visible spectrum (654 nm) laser operation of a single 7.5 ML InP QD layer coupled by a 20-Å In _0.5Al_0.3Ga_0.2P barrier to an auxiliary 70-Å In_0.5Ga_0.5P QW. The simple stripe-geometry (530 μm × 10 μm) InP QD + InGaP QW heterostructure laser, enhanced by the QW and operating on an upper QD state (42% quantum efficiency), is capable of over 10-mW/facet cw 300-K operation in spite of the weak heat sinking of probe operation.; Data are presented demonstrating the cw 300-K visible spectrum of a 642-nm, 646-nm and 654-nm QD+QW laser. Data indicate that stronger coupling between QW and QD layers results in better (weaker) wavelength shift versus temperature characteristics (Δλ/ΔT ∼ 0.13nm/°C for strong coupling and ∼0.19nm/°C for weak coupling).; Data are presented showing that the gain of a QD laser is improved by strong resonance-enhanced coupling of QD states to MQW states for pulsed laser operation between λ = 607 and 619.7 nm.; Despite the use of tensile strained MQWs (strong TM radiation recombination), pulsed laser operation with TE polarization is observed.; Data (infrared wavelengths) are presented showing that it is advantageous to locate strain-matching auxiliary InGaAs layers QWs within tunneling distance of a single QD layer of an AlGaAs-GaAs-InGaAs-InAs QD heterostructure laser to realize also smaller size QDs of greater density and uniformity. (Abstract shortened by UMI.)