Simulation of output power and optical gain characteristics of self-assembled quantum-dot lasers: Effects of homogeneous and inhomogeneous broadening, quantum dot coverage and phonon bottleneck

Abstract

The effects of temperature (homogeneous broadening (HB)) on output power, gain spectrum, and light–current (L–I) characteristics of self-assembled quantum-dot lasers (SAQDLs) are investigated. We also analyze the effects of inhomogeneous broadening (IHB) and QD coverage on L–I characteristics and the effects of carrier relaxation and recombination lifetimes on L–I and optical gain–current characteristics. We propose the possibility of single mode lasing for every HB that is comparable, near, or equal to IHB and for every lasing injected current. We also show that peak optical gain does not change with variations of temperature (HB) and injected current. Simulation of L–I characteristics shows that L–I curves become nonlinear as HB elevates up to near IHB. Exceeding HB from IHB and elevating IHB result in degradation of L–I characteristics. Threshold current grows as temperature (HB) enhances. It is, therefore, concluded that the SAQDL has the best L–I characteristics when HB is equal to IHB. It is also shown that there is a threshold and an optimum QD coverage. We reveal that the phonon bottleneck degrades L–I characteristics and that the maximum output power decreases significantly with enhancement of IHB. Finally, we show that the phonon bottleneck, low wetting layer and QD crystal quality reduce the differential gain, relaxation oscillation frequency and modulation bandwidth.