High performance lasers and spin-polarized light emitting diodes with quantum dot active regions

The modulation bandwidth of conventional 1.0--1.3 mum self-organized In(Ga)As quantum dot (QD) lasers is limited to ∼6--8 GHz due to hot carrier effects arising from the predominant occupation of wetting layer/barrier states. Thermal broadening of holes in the valence band of QDs also limits the performance of these lasers in modulation bandwidth and characteristic temperature, T0. Tunnel injection and p-doping have been investigated in order to alleviate these problems. Finally, distributed feedback (DFB) QD lasers have been studied as single mode sources, circumventing problems associated with the broad emission encountered in Fabry-Perot lasers.; Loss-coupled InGaAs/GaAs 1.0 mum QD DFB lasers with 30 dB side-mode suppression ratio and single-mode lasing linewidth of 4 A at room-temperature has been demonstrated. High-performance p-doped ln(Ga)As/GaAs QD lasers emitting at 1.3 and 1.1 mum are reported. Zero dependence of slope efficiency and threshold current (infinite T0) from 5 to 75°C is reported in 1.3 mum p-doped QD lasers, the first in any semiconductor laser, which is attributed to the significant role of Auger recombination in QD lasers and its decrease with temperature. P-doped QD lasers exhibit only a few GHz improvement of modulation bandwidth as compared with undoped lasers.; The impact of utilizing both p-doping and tunnel injection in the characteristics of 1.1 mum QD lasers was studied and compared with undoped tunneling injection lasers. Higher modulation bandwidth (∼25 GHz) and differential gain (3 x 10-14 cm2) are measured in p-doped tunnel injection lasers with T0 ∼ 205 K from 5 to 95°C. The p-doped tunnel injection QD lasers exhibit zero linewidth enhancement factor and negligible chirp (<0.4 A). These dynamic properties of QD lasers surpass those of equivalent quantum well lasers.; Future 80 GHz wavelength division multiplexing systems require optical sources with more challenging bandwidths which may be acquired by utilizing carriers spin as an extra modulation scheme. Operation of spin-polarized light emitting diodes with GaMnAs spin-aligning layer is demonstrated at ∼90 K with a high output light polarization of 30% at 4.5 K. Curie temperatures above 300 K is demonstrated in InMnAs self-organized diluted magnetic quantum dots for future room-temperature spintronic applications.