The History of p-n Junction Discovery, or the Beginnings of the Transistor
Transistors were invented half a century ago, and remain the foundation of modern digital technology. But who discovered the physical phenomena and basic principles underpinning their development? To answer this question we reveal a shining moment in the history of IT development in Ukraine, and the work of an outstanding physicist: Vadim Yevgenyevych Lashkaryov.
In 1956, in a Stockholm concert hall, three American scientists, John Bardeen, William Shockley, and Walter Brattain, received the Nobel prize “for research in semiconductors and the discovery of transistor effect”. This represented a major breakthrough in physics, and ensured their names would be forever etched in the history of science. However, they were not the only ones to carry out such research.
Fifteen years earlier, at the beginning of 1941, a young scientist called Vadim Lashkaryov published an article describing how two sides of a “barrier layer”, located parallel to the interface between copper and cuprous oxide, would exhibit opposite signs of charge carriers. Afterwards, this discovery would be named “p-n junction” (p for “positive”, n for “negative”), and be the phenomenon underpinning the scientific breakthrough for which the Americans were awarded the Nobel prize. In addition, Lashkaryov’s article revealed the injection mechanism, a crucial phenomenon providing the operational basis of semiconductor diodes and transistors. Unfortunately, Lashkaryov’s research did not reach the West and so he did not receive the credit that his work deserved.
The official history of transistor begins with the first public announcement of the advent of the semiconductor amplifier-transistor, which appeared in American press in July 1948. The invention was credited to the American scientists Bardeen and Brattain, who had been working to create a so-called point-contact transistor based on n-type germanium crystal. They achieved their first promising results in late 1947, but the apparatus was unstable and behaved unpredictably, and thus their point-contact transistor had found no practical use.
The breakthrough came in 1951 when William Shockley created his more reliable n-p-n type junction transistor consisting of three n, p, and n type germanium layers of one centimeter overall thickness. Within just these few short years, the significance of the American scientists’ invention became obvious, and they were awarded the Nobel prize.
Yet long before these events, and before the beginning of the Great Patriotic War in 1941, Lashkaryov had carried out a series of successful experiments, discovering р-n junction and revealing the hole-electron diffusion mechanism. Following this, in the early 1950’s, semiconductor triodes (what became termed transistors) were first created in the Ukraine, then part of the USSR, under Lashkaryov’s management.
Given the importance of this discovery to computing, it is helpful to understand in a little more detail. In scientific language, p-n junction is a region of space at the interface of two semiconductors of p and n type where a transition occurs from one type of conductance to another. Electric conductance of a material depends on how strongly the nuclei of its atoms keep hold of electrons. E.g., most metals are good conductors as they possess a huge amount of electrons weakly bound to their atoms’ nuclei, and these electrons are easily attracted by positive charges and repulsed by negative charges. Such electrons on the move are carriers of electric current. On the other hand, dielectrics do not let current through because electrons in them are strongly bound to atoms and do not respond to the action of an external electric field.
Semiconductors behave in a different manner. The atoms in the crystals of semiconductors form a lattice in which outer electrons are bound by forces of a chemical nature. In pure form, semiconductors are like dielectrics: they transmit current poorly or not at all. However, as soon as a small amount of atoms of certain elements (admixtures) is added to the crystal lattice, their behavior changes dramatically.
In some cases, atoms from the admixture become bound to the semiconductor’s atoms releasing redundant electrons, and the excess of free electrons imparts negative charge to the semiconductor. In other cases, admixture atoms generate the so-called “holes” capable of absorbing electrons. In this way, a deficit of electrons occurs, and the semiconductor becomes positively charged. Under the appropriate conditions, semiconductors can transmit electric current. However, as distinct from metals, they transmit it in dual manner. Negatively charged semiconductors strive to get rid of excess electrons; this is n-type conductance (from “negative”). Electrons act as carriers of charge in semiconductors of this type. On the other hand, positively charged semiconductors attract electrons to fill in their “holes”. However, when one hole is filled in, another is created next to it - the one abandoned by the electron. In this manner, holes generate a flow of positive charge directed opposite to the movement of electrons. This is р-type conductance (from “positive”). In both types of semiconductors, the so-called minority carriers of charge (electrons in р-type semiconductors and holes in n-type semiconductors) support current in the direction opposite to the direction of majority charge carriers’ movement.
By introducing admixtures to germanium or silicon crystals, it is possible to create semiconductor materials possessing desirable electric properties. For instance, introducing a small amount of phosphorus produces free electrons and the semiconductor then assumes n-type conductance. In contrast, adding boron atoms causes the emergence of holes, and the material becomes a р-type semiconductor.
Thus, it was discovered that a semiconductor mixed with admixtures was able to conduct an electric current; the value of which, under certain influences, may be varied within broad limits.
When a method was discovered in USA to exert such influence electronically, the transistor was born (from the initial denomination “transresistor”).
In addition to his first two works, in 1950 Lashkaryov jointly published an article with V. I. Lyashenko, titled “Electronic States on the Surface of a Semiconductor” article which presented the results of results into semiconductors surface phenomena. These phenomena became the operational foundation for integrated circuits based on field transistors.
In the 1950’s, Lashkaryov also managed to solve the problem of mass rejection of germanium mоnоcrystals, by revising the technical requirements. Rigorous research carried out by Lashkaryov and Miselyuk at the Institute of Physics of the Academy of Sciences of the Ukrainian SSR in Kyiv, revealed that the existing level of germanium monocrystals technology could already create point-contact diodes and triodes possessing the required characteristics. This made it possible to accelerate the industrial production of the former USSR’s first germanium diodes and transistors.
Following this discovery, in the early 1950’s production of the first point-contact transistors was organized under Lashkaryov’s management. He also formed a scientific school in the field of semiconductor physics, which became one of the leading schools in the USSR. The founding of the Institute of Semiconductors of the Academy of Sciences of Ukraine with V. E. Lashkaryov as its head in 1960 was further recognition of the outstanding results achieved.
“In the future this tiny crystal that Vadim Yevgenyevych shows us will contain a whole computer!” Academician Sergey Lebedev, who created the continental Europe’s first computer (MESM), predicted. History has proved him right, although it took more than 20 years before large-scale integration circuits (LSIs) came into being, containing tens and hundreds of thousands of transistors on a crystal, and later, the super large scale integration circuits (VLSIs) containing many millions of components, paving the way to today’s information age.