Abstract
Various theoretical as well as empirical considerations about how to achieve lasing between the conduction and valence bands in indirect band gap semiconductors (germanium and silicon) are reviewed, starting from the dawn of the laser epoch in the beginning of the sixties. While in Ge the room-temperature lasing under electrical pumping has recently been achieved, in Si this objective remains still illusory. The necessity of applying a slightly different approach in Si as opposed to Ge is stressed. Recent advances in the field are discussed, based in particular on light-emitting Si quantum dots.
Highlights
After the pioneer publications describing the successful realization of the first semiconductor lasers (1962) on gallium arsenide GaAs [1,2,3,4], which is a direct band gap material, considerations appeared if lasing could be achieved in indirect band gap semiconductors
The reason was obvious: At that time, it was germanium that represented the material base of semiconductor electronics, being gradually replaced by silicon, a semiconductor with better noise properties due to the wider Si band gap
The difference between direct and indirect optical transitions as regards the probabilities of electron–hole radiative recombination was already well known: in indirect-gap semiconductors this probability had been known to be lower by many orders
Summary
After the pioneer publications describing the successful realization of the first semiconductor lasers (1962) on gallium arsenide GaAs [1,2,3,4], which is a direct band gap material, considerations appeared if lasing could be achieved in indirect band gap semiconductors. The reason was obvious: At that time, it was germanium that represented the material base of semiconductor electronics, being gradually replaced by silicon, a semiconductor with better noise properties due to the wider Si band gap (and, thereby, a lower thermal noise in Si devices operating at room temperature). Both these materials have indirect band gap (Figure 1), common knowledge already in the beginning of the 1960’s. To put it differently, to convert the case of Ge or Si to the GaAs case
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