Quantum dot lasers: from promise to reality

Abstract

Nanoscale coherent insertions of narrow gap material in a single-crystalline matrix, or Quantum Dot (QD) provide a possibility to extend the basic principles of heterostructure lasers. The idea to use heterostructures with dimensionality lower than two in semiconductor lasers appeared a quarter of a century ago, simultaneously with the proposal of a quantum well laser. However, fabrication of quantum wire- and, particularly, QD heterostructure (QDHS) lasers appeared to be much more difficult. The breakthrough occurred when techniques for self-organized growth of QDs allowed fabrication of dense arrays of uniform in shape and size coherent islands free from undesirable defects. Recently, some key parameters of QD lasers were significantly improved as compared to those for QW devices. High-power operation, record low threshold current densities, strongly reduced chirp and extension of the wavelength range on GaAs substrates up to 1.3 micrometer range were demonstrated. It also became clear that unique properties of QDs may give rise to a new generation of semiconductor lasers, such as far and middle infrared light emitters based on interlevel electron transitions in QDs or single quantum dot vertical-cavity surface-emitting lasers.