Semiconductor Spin-Lasers

Authored by: Igor Žutić , Rafał Oszwałdowski , Jeongsu Lee , Christian Gøthgen

Handbook of Spin Transport and Magnetism

Print publication date:  August  2011
Online publication date:  April  2016

Print ISBN: 9781439803776
eBook ISBN: 9781439803783
Adobe ISBN:

10.1201/b11086-45

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Abstract

The word laser is an abbreviation for light amplification by stimulated emission of radiation. However, considering its modern applications, it is perhaps better viewed as a light-generating device, rather than a light amplifier [1]. The operating principles of lasers can be traced back to the prediction of stimulated emission by Albert Einstein in 1917 [2]. One of the key laser characteristics is dependence of the emitted light on pumping or injection. We will distinguish conventional lasers and spin-lasers depending if this pumping/injection introduces spin-unpolarized or spin-polarized carriers, respectively. Typically, in conventional lasers two regimes are distinguished. For low pumping there is no stimulated emission, laser operates as an ordinary light source: the emitted photons are incoherent. However, the higher pumping regime with stimulated emission and coherent light makes the laser such a unique light source. The intensity of pumping/injection above which there is a phase-coherent emission of light is called the lasing threshold. Important advances in semiconductor lasers can be associated with the reduction of threshold current density for the onset of lasing. It could be shown that such a reduction would not only decrease the power consumption of lasers but can also significantly enhance their dynamic performance [4]. A schematic illustration in Figure 38.1 shows the historical evolution of threshold reduction in semiconductor lasers, realized by gradually replacing a bulk-like active region (known also as the gain medium, where the lasing action takes place) with structures of reduced dimensionality: quantum wells (QWs), quantum wires, and quantum dots (QDs).

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