Double heterostructures are the basis of semiconductor lasers, which have changed our daily life considerably, from bar code scanners at supermarket checkouts to the World Wide Web communication that relies on fast signal transduction via fiber-optic cables. In principle, their mode of action was invented independently by Herbert Kroemer and Zhores Alferov in 1963: An electric current induces an inverse population state within a thin semiconductor layer that is sandwiched between two other heterostructures and triggers the upright emission of laser light from that layer. Yet it was necessary to find the material in which this principle could be best harnessed so that semiconductor lasers would work continuously and at room temperature to practically apply them, as Alferov explains in this lecture. While the commercial development of such laser diodes was pioneered by American companies in the seventies, it was Zhores Alferov’s group who first succeeded in constructing their prototype by using a lattice of aluminum gallium arsenide and gallium arsenide in their laboratory at the Ioffe Institute in Leningrad in 1970.

His lecture could also be called “recent research on heterostructures at the Ioffe Institute”, Alferov says, whereby “recent for old people like me means approximately 40 years“. As the fifth director and fifth Nobel Prize Winner of the Ioffe Institute, he proudly presents some of the achievements of this institute, which had „started as a seminar on new physics in 1916” conducted by Abram Ioffe at the Polytechnical Institute in Saint Petersburg (which was named Leningrad between 1924 and 1991). His predecessors as Ioffe Institute affiliated Nobel Prize Winners were Nikolay Semenov (Chemistry 1956), Igor Tamm (Physics 1958), Lev Landau (Physics 1962) and Pyotr Kapitsa (Physics 1978). For Alferov himself, it was of symbolic significance that he shared one of the Nobel Prizes in Physics with Herbert Kroemer in the year 2000, as he stated in his Banquet Speech in Stockholm: „The Nobel Prize in Physics 2000, at the change of centuries, has a special meaning. The twentieth century was not only the century of wars and social explosions, it was the century of Physics and first of all quantum Physics...Just after the World War II discovery of the transistor and laser-maser principles - became the roots of information technology of the XX-th century. Invention of integrated circuits and creation of a new kind of materials - "Man-made crystals" - semiconductor heterostructures - led to the modern level of information and communication technology.“[1]

The distinction between „god-made and man-made crystals“, originally introduced by Leo Esaki (Nobel Prize in Physics 1973), is the leitmotif of Alferov’s lecture. „You can consider heterostructures in general as man-made crystals“, he says and invites his audience to follow him on a journey through the history of heterostructure research, „from the classical physical phenomenon, which happens in bulk heterostructures“ via super lattices, quantum well and quantum wire heterostructures to the growing of quantum dots within semiconductors, „the most dramatic story, which is going on now“.

Heterostructures have not only found many useful applications in lasers, light emitting diodes or solar cells, Alferov says, they also have enabled the discovery of very important physical phenomena, namely the quantized Hall effect (Nobel Prize in Physics 1985) and the fractional quantum Hall effect (Nobel Prize in Physics 1998), „in my consideration the most important discoveries in physics in the last three decades“. Alferov explains why quantum dots can be regarded as artificial atoms and what their future prospects are. Eleven and a half years later, quantum dots were used for the first time in a mass-produced consumer electronics product[2].

Joachim Pietzsch

[1] http://www.nobelprize.org/nobel_prizes/physics/laureates/2000/alferov-speech.html

[2] Quantum dots get commercial debut in more colorful Sony TVs. MIT Technology Review January 11, 2013. 
http://www.technologyreview.com/news/509801/quantum-dots-get-commercial-debut-in-more-colorful-sony-tvs/