CPM Seminar

High Performance Quantum Dot Lasers on GaAs and Si

Zetian Mi

Department of Electrical and Computer Engineering
McGill University

The desirable characteristics of a semiconductor laser required for optical communications and related applications include large modulation bandwidth, uncooled operation, and small chirp and α-parameter. One of the materials of choice is self-organized InAs quantum dots (QDs) grown on GaAs or Si substrates. Conventional QD lasers, however, suffer from hot carrier problems due to the presence of a two-dimensional wetting layer and closely spaced hole energy levels, leading to large temperature dependence of the threshold current and small modulation bandwidth. Special techniques, such as p-doping and tunnel injection, have been demonstrated to be very effective in alleviating these problems to a large extent. In the scheme of tunnel injection, cold carriers are directly injected into the lasing ground states of QDs by phonon assisted tunneling from the injector well, leading to minimized hot carrier effects and greatly increased differential gain and modulation bandwidth. P-doping, on the hand, provides excess holes in the dots. Deleterious effects, such as carrier spreading and gain compression due to thermally broadened hole distributions, can be largely eliminated. The effectiveness of these special techniques, as well as the performance of InAs QD lasers are, ultimately, strongly influenced by the quality and spectral broadening of the dots. In this context, I will present our recent studies on the growth and characteristics of p-doped and tunnel injection QD lasers on GaAs and Si. The lasers exhibit nearly ideal characteristics, such as ultralow threshold current (~ 60 A/cm²), temperature invariant operation (T₀≈∞), large modulation bandwidth (f_-3dB = 24.5 GHz), and near-zero α-parameter and very low chirp (~ 0.1 Â).