The intermediate-band solar cell (IBSC) has been proposed as a high-efficiency solar cell because of the extended absorption it allows for, which results from the intermediate band. In order to further increase the efficiency of IBSCs, we study a novel device with dual intermediate bands. Because of the extended absorption from the second intermediate band, the efficiency of a dual IBSC can reach 86.5% at a full concentration. Moreover, we study the performance of the IBSC based on InAs/InGaAs quantum dots. The efficiency of the device is shown to be able to reach 74.4% when the In composition is 75%. In addition, the transition process between the dual intermediate bands greatly affects the efficiency, so it is important to design the dual intermediate bands in a precise manner.

A core–shell nanowire heterostructure is an important building block for nanowire-based optoelectronic devices. In this paper, the shape and composition evolution induced by adatom diffusion is investigated by constructing a growth model for alloy core–shell nanowire heterostructures, taking diffusion, adsorption, desorption and incorporation of adatoms into consideration. With moving boundaries accounting for sidewall growth, the transient diffusion equations are numerically solved by the finite element method. The adatom diffusions introduce the position-dependent and time-dependent adatom concentrations of components A and B. The newly grown alloy nanowire shell depends on the incorporation rates, resulting in both shape and composition evolution during growth. The results show that the morphology of nanowire shell strongly depends on the flux impingement angle. With the increase in this impingement angle, the position of the largest shell thickness on sidewall moves down to the bottom of nanowire and meanwhile, the contact angle between shell and substrate increases to an obtuse angle. Coupled with the shell shapes, the composition profiles are shown as non-uniform along both the nanowire and the shell growth directions, which can be attributed to the adatom diffusion of components A and B. The impacts of parameters on the shape and composition evolution are systematically investigated, including diffusion length, adatom lifetime and corresponding ratios between components. This kinetic model is expected to interpret the contribution of adatom diffusion in growing alloy group-IV and group III-V core–shell nanowire heterostructures.

Aiming to realize high-speed optical transmitters for isolator-free telecommunication systems, 1.3 μm p-modulation doped InGaAs/GaAs quantum dot (QD) lasers with a 400 μm long cavity have been reported. Compared with the un-doped QD laser as a reference, the p-doped QD laser emits at ground state, with an ultra-low threshold current and a high maximum output power. The p-doped QD laser also shows enhanced dynamic characteristics, with a 10 Gb/s large-signal direct modulation rate and a 7.8 GHz 3dB-bandwidth. In addition, the p-doped QD laser exhibits a strong coherent optical feedback resistance, which might be beyond −9 dB.