Super-gain nanostructure with self-assembled well-wire complex energy-band engineering for high performance of tunable laser diodes

Abstract

Although traditional quantum-confined nanostructures e.g. regular quantum wells or quantum dots have achieved huge success in the field of semiconductor lasers for past decades, these traditional nanostructures are encountering the difficulty of enhancing device performance to a higher level due to their inherent gain bottleneck. In this paper, we are proposing a new super-gain nanostructure based on self-assembled well-wire complex energy-band engineering with InGaAs-based materials to break through the existing bottleneck. The nanostructure is constructed by utilizing the special strain-driven indium (In)-segregation and the growth orientation-dependent on-GaAs multi-atomic step effects to achieve the distinguished ultra-wide and uniform super-gain spectra. The structural details and its luminescence mechanism are investigated by multiple measurement means and theoretical modeling. The polarized gain spectra with the max fluctuation of <3 cm−1 in 904 nm–998 nm for transverse electric (TE) mode and 904 nm–977 nm for transverse magnetic (TM) mode are simultaneously obtained with this nanostructure. It enables an ultra-low output power fluctuation of <0.7 dB and a nearly-constant threshold power throughout an ultra-wide wavelength range under a fixed injection level. It was difficult to realize these in the past. Therefore, the described super-gain nanostructure brings a brand-new chance of developing high performance of tunable laser diodes.

Ultra-broadband depolarization based on directly-coupled quantum wire-to-well modulation and their aliasing effect for polarization-insensitive light-emitting diodes

“…Owing to the one-dimensional quantum wires combining directly with the well in the directly-coupled well–wire regions, the band-gap is increased in this part compared with the pure-well part of the nanostructure. 32,41 Thus, peak A in the ASE spectrum in Fig. 3(a) comes from the directly-coupled well–wire region emission, while peak B is generated by the pure-well regions of the whole nanostructure.…”

“…This is achieved by utilizing the orientation-dependent on-GaAs multi-atomic step effect in the material growth. 32–34 A high In-content of 0.17 is applied for the InGaAs active structure (including the well and wires), ensuring that the strain-driven In-segregation effect would occur and promoting In-atom migration under the In-segregation effect during the material growth. 35,36 Owing to the In-segregation effect, the In-contents in both well and wires would vary continuously along the growth direction, resulting in the band-gap of the active structure changing accordingly.…”

“…All the above structural characterization data are consistent with our previous research results. 32,33…”

“…In view of the above considerations, we are proposing a novel depolarization solution and the corresponding quantum structure to realize ultra-broadband depolarization for strained light-emitting diodes. It is based on a kind of quantum well–wire-hybrid nanostructure recently proposed by our group, 32,33 where the quantum wires are formed directly on the well in a self-assembling way. This hybrid quantum-confined structure has displayed some special advantages over traditional quantum wells or dots.…”

“…However, as it is a new material structure, many of its physical properties and relevant mechanisms that may be different from those of traditional quantum structures are still unknown and have not been widely investigated so far. Previous research on this hybrid quantum-confined nanostructure focused mainly on its gain-broadening (super-gain) property due to the joint role of well and wires, 32 as well as the improvement in the high-temperature performance of the device due to the reduction in non-radiative recombination under the action of quantum wires. 33 Recently, a distinguished depolarization property due to wire-to-well strain modulation in this well–wire-hybrid nanostructure was observed in our experiments for the first time.…”