Nobel Prize in Physics 2000: Semiconductor Heterostructures and the Integrated Circuit

This note covers the Nobel Prize in Physics 2000: who won it, what semiconductor heterostructures and the integrated circuit are, how transistors and lasers became fast and small, how the discoveries unfolded, why they matter, and quick facts for exams.

What was the Nobel Prize in Physics 2000 awarded for?

The Nobel Prize in Physics 2000 was given "for basic work on information and communication technology". The Royal Swedish Academy of Sciences split the prize into two equal halves, one of which was shared. One half went jointly to Zhores I. Alferov and Herbert Kroemer "for developing semiconductor heterostructures used in high-speed- and opto-electronics", and the other half went to Jack S. Kilby "for his part in the invention of the integrated circuit".

In plain words, the three laureates were honoured for the physics that made modern electronics fast and small at the same time.

Alferov and Kroemer worked out how to build layered semiconductor sandwiches, called heterostructures, that made transistors and lasers run at very high speed.

Kilby showed that many separate electronic parts could be built into one single block of semiconductor material, the integrated circuit or "chip". Together, these two lines of work became the physical foundation of computers, mobile phones and the Internet.

The official name of this award is the Nobel Prize in Physics. It was announced on 10 October 2000 and the prize amount was 9,000,000 Swedish kronor, shared with one quarter each to Alferov and Kroemer and one half to Kilby.

Who are the laureates?

Zhores I. Alferov

Zhores I. Alferov was born on 15 March 1930 in Vitebsk, Belorussia, in the USSR (in what is now Belarus), and he died on 1 March 2019 in St. Petersburg, Russia.

At the time of the award he worked at the A.F. Ioffe Physico-Technical Institute in St. Petersburg, where he had been director since 1987. He received one quarter of the prize.

In 1963, independently of Kroemer, Alferov worked out the principle of a heterostructure laser, and his research team went on to build the first lasers of this kind that could run continuously at room temperature.

Herbert Kroemer

Herbert Kroemer was born on 25 August 1928 in Weimar, Germany, and he died on 8 March 2024. At the time of the award he was affiliated with the University of California, Santa Barbara, in the United States.

He received one quarter of the prize. In 1957, while working at RCA, Kroemer put forward the first detailed proposal for a heterostructure transistor, and in 1963, independently of Alferov, he proposed the principle of the double heterostructure laser.

Jack S. Kilby

Jack S. Kilby was born on 8 November 1923 in Jefferson City, Missouri, USA, and he died on 20 June 2005 in Dallas, Texas, USA. At the time of the award he was affiliated with Texas Instruments in Dallas.

He received one half of the prize, the largest single share. During the summer of 1958, while working alone in the laboratory, Kilby showed that an oscillator's separate components could all be fabricated from a single semiconductor material, and on 12 September 1958 he demonstrated a complete electronic circuit built from a single piece of semiconductor material; in February 1959 he filed a patent for this "Miniaturized Electronic Circuits".

What problem were these inventions trying to solve?

By the middle of the twentieth century, electronic equipment such as radios and early computers used vacuum tubes, which were bulky, fragile and wasted a great deal of energy as heat.

The invention of the transistor around Christmas 1947, honoured by the 1956 Nobel Prize in Physics, gave engineers a smaller and more reliable solid-state part that could switch and amplify electrical signals.

But transistors still had to be soldered one by one onto circuit boards along with resistors and capacitors.

As computers needed tens of thousands of components, soldering became slow, unreliable and a serious bottleneck: the number of transistors that could practically be wired together was limiting how powerful a machine could be.

At the same time, the transistors of that era were also too slow for high-frequency uses such as satellite links and later mobile telephony, because of resistance and capacitance effects inside an ordinary transistor's base region.

So electronics faced two separate but related problems that this prize's laureates each attacked. The first was a problem of complexity: how to connect enormous numbers of components without hand-soldering each one.

The second was a problem of speed: how to make transistors and light sources fast enough for high-frequency communication and for driving long optical fibres. Kilby's integrated circuit answered the first problem, while Alferov and Kroemer's heterostructures answered the second.

How does the integrated circuit work?

An integrated circuit, or chip, is a single piece of semiconductor crystal on which many active parts (such as transistors) and passive parts (such as resistors and capacitors) are built together and connected by thin metal strips, instead of being made separately and soldered by hand.

Kilby's insight in 1958 was that all these different components could be fabricated from the same block of semiconductor material rather than from different, cheaper materials as industrial practice then assumed.

1. A single crystal of semiconductor material (first germanium, later mainly silicon) is grown and sliced into thin wafers.
2. Different regions of the wafer are treated so that some areas act as transistors, others as resistors and others as capacitors, all on the same piece of material.
3. Thin conducting strips are laid down on top to connect these regions electrically, replacing the separate soldered wires of older circuits.
4. The finished wafer is cut up into many identical chips, each containing a complete working circuit.

Kilby demonstrated a working circuit of this kind on 12 September 1958 and filed a patent application for "Miniaturized Electronic Circuits" on 6 February 1959.

Working independently at Fairchild, Robert Noyce later showed that aluminium adhered well to silicon and silicon dioxide, which became the practical interconnect method used in industry.

Kilby and Noyce are both regarded as co-inventors of the integrated circuit, but only Kilby received the Nobel Prize, since Noyce had died in 1990 and the prize is not normally awarded after death.

The number of components that can fit on one chip has grown enormously since 1960, a trend popularly known as Moore's law, which observed that chip performance roughly doubles every eighteen to twenty-four months.

Draw three boxes side by side: a bulky vacuum tube, a small single transistor, and a flat chip containing many tiny transistors, resistors and capacitors joined by thin connecting lines, to show the shrinking of electronics across these three stages.

How do semiconductor heterostructures make fast transistors and lasers?

A semiconductor is a material whose ability to conduct electricity lies between that of a good conductor (like copper) and an insulator (like glass).

A heterostructure is built by growing several very thin layers of different semiconductor materials, such as gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs), one on top of another, so that each layer has a different band gap, the amount of energy needed to free an electron to move and carry current.

Kroemer proposed in 1957 that if the base of a transistor were made from a material with a smaller band gap than the surrounding layers, electrons could flow through it far more easily while unwanted current in the opposite direction stayed low, giving much higher amplification at high frequencies.

In a heterostructure laser, a very thin layer with a smaller band gap is sandwiched between two layers with a larger band gap.

This "double heterostructure", proposed independently by Alferov and Kroemer in 1963, traps both the moving electrons and holes and the light particles (photons) they produce inside the thin middle layer, which lets the laser work continuously at room temperature instead of needing extra cooling.

Alferov's research group at the Ioffe Institute in Leningrad (now St. Petersburg) achieved a pulsed double heterostructure laser in late 1968 and reported a laser that worked continuously at room temperature in May 1970, a few weeks ahead of competing American groups working at the same problem.

Draw three horizontal layers: a thin middle layer with a small band gap sandwiched between two outer layers with a larger band gap, with arrows showing electrons and holes meeting in the thin middle layer and photons being emitted from it, to show how light and current carriers are both trapped in the same narrow region.

How did the discovery unfold?

Why does this work matter?

The Academy's presentation speech described this prize as rewarding the physics behind microelectronics and photonics that underlie almost every modern information device.

Chips built as integrated circuits became, in the Academy's words, components "now in all modern electronics", running everything from washing machines and cars to computers and medical scanners.

Heterostructure transistors made possible the fast, low-noise amplifiers used in satellite links and mobile phone base stations, while heterostructure lasers made continuous, room-temperature light sources possible for optical-fibre communication, CD players and bar-code readers.

The press release for the prize noted that the laureates' inventions laid "a stable foundation for modern information technology", a foundation that let information technology spread through society far faster than earlier technologies such as the printed book.

Heterostructures also opened up pure physics research: the two-dimensional layer of electrons formed at a heterojunction boundary was the experimental setting used for the quantum Hall effect, recognised by the 1985 and 1998 Nobel Prizes in Physics.

Open questions remain about how long continued miniaturisation of chips can continue, since both the physical limits of atomic-scale materials and the rising cost of manufacturing equipment set practical boundaries on how far "Moore's law" style doubling can go.

How does this connect to what you study?

Students who study electricity and semiconductors in physics will recognise the transistor as a basic switching device, and this prize explains how transistors were combined into integrated circuits and made faster using layered heterostructures.

The idea of a band gap, the amount of energy needed to free an electron in a material so that it can carry current, connects directly to classroom discussions of conductors, insulators and semiconductors, since a semiconductor's band gap lies between the two extremes.

The laser diode explained here also links to the general physics idea of light being produced when electrons and holes recombine inside a material, releasing energy as photons. A student who has studied how current flows through a junction can extend that idea to see how stacking two junctions together, as in a double heterostructure, confines both the moving charges and the light they produce to one thin layer.

The chapter on digital electronics or computer basics taught in many schools also connects here: the integrated circuit that Kilby helped invent is the physical object inside every logic gate and memory chip that a student might draw as a block diagram, so understanding how many components fit onto one chip gives a concrete picture behind that classroom diagram.

Finally, the mention of satellite links and mobile telephone base stations ties this prize to any lesson on communication systems, since the heterojunction transistors described here are the real components that make those weak, high-frequency signals usable.

Quick facts for exams

The Nobel Prize in Physics 2000 was awarded "for basic work on information and communication technology". It was announced on 10 October 2000 by the Royal Swedish Academy of Sciences. One half went jointly to Zhores I. Alferov and Herbert Kroemer for developing semiconductor heterostructures used in high-speed- and opto-electronics, and the other half went to Jack S. Kilby for his part in inventing the integrated circuit. Alferov worked at the A.F. Ioffe Physico-Technical Institute in Russia, Kroemer at the University of California, Santa Barbara in the USA, and Kilby at Texas Instruments in the USA. The total prize amount was 9,000,000 Swedish kronor.

Note: Source. The prize facts in this note are from the Nobel Prize's official site, nobelprize.org.

Glossary

• Semiconductor — a material whose ability to conduct electricity lies between that of a conductor and an insulator.
• Band gap — the amount of energy needed to free an electron so it can move and carry current in a material.
• Heterostructure — a structure built from several thin layers of different semiconductor materials, each with a different band gap.
• Transistor — a solid-state device that can switch or amplify an electrical signal.
• Integrated circuit — a single piece of semiconductor material on which many components and their connections are built together.
• Heterojunction transistor — a transistor whose base layer has a smaller band gap than the surrounding layers, giving higher speed and lower noise.
• Double heterostructure laser — a laser in which a thin low-band-gap layer between two higher-band-gap layers confines electrons, holes and light to produce continuous laser light.
• Photon — a particle of light, released when an electron and a hole recombine inside a semiconductor laser or light-emitting diode.
• Light-emitting diode (LED) — a semiconductor device built with a similar layered design to a laser diode that emits light without lasing.
• Moore's law — the observation that the number of components that fit on a chip roughly doubles every eighteen to twenty-four months.
• Two-dimensional electron gas — a thin sheet of electrons that forms at the boundary between two layers of a heterostructure.
• Opto-electronics — electronic devices, such as lasers and light-emitting diodes, that work by producing or detecting light.

Common errors and misconceptions

• Misconception: Jack Kilby invented the integrated circuit entirely alone. Correct: Robert Noyce independently developed the version using aluminium connectors that became the practical industry standard, so the two are generally regarded as co-inventors, though only Kilby could receive the Nobel Prize since Noyce had already died.
• Misconception: all three laureates worked on the same invention. Correct: Alferov and Kroemer worked on heterostructures for fast transistors and lasers, while Kilby worked separately on the integrated circuit; the two lines of work were recognised together under one broad citation.
• Misconception: a heterostructure is just a very small transistor. Correct: a heterostructure is a layered combination of different semiconductor materials with different band gaps, which can be used to build many kinds of devices, including transistors, lasers and light-emitting diodes.
• Misconception: semiconductor lasers were first made to work continuously at room temperature in the United States. Correct: Alferov's team in Leningrad reported continuous room-temperature operation in May 1970, a few weeks before the competing American group.
• Misconception: the integrated circuit and the microprocessor are the same invention. Correct: the integrated circuit, demonstrated by Kilby in 1958, was followed roughly ten years later by the microprocessor, which packed enough components onto one chip to form a complete computer processor.
• Misconception: the prize money was shared equally among the three laureates. Correct: Alferov and Kroemer each received one quarter of the prize, while Kilby alone received one half.

Exam-style questions with model answers

Q1. What was the official citation for the Nobel Prize in Physics 2000? [2 marks]

1. The prize was awarded "for basic work on information and communication technology", split between heterostructure work by Alferov and Kroemer and the integrated circuit invented in part by Kilby.

Q2. Name the three laureates of the Nobel Prize in Physics 2000 and state their affiliations at the time of the award. [2 marks]

1. Zhores I. Alferov was at the A.F. Ioffe Physico-Technical Institute in Russia, Herbert Kroemer was at the University of California, Santa Barbara, and Jack S. Kilby was at Texas Instruments, both in the USA.

Q3. Explain what a semiconductor heterostructure is and why it helps make fast transistors. [4 marks]

1. A heterostructure is built from several thin layers of different semiconductor materials, each with a different band gap, grown one on top of another.
2. In a heterojunction transistor, the base layer has a smaller band gap than the layers around it.
3. This lowers the barrier for the electrons that carry useful current, while the unwanted hole current flowing the other way stays about the same.
4. The result is a transistor that amplifies more strongly and works at much higher frequencies, with lower noise, than an ordinary transistor made from a single material.

Q4. Describe how Jack Kilby developed the integrated circuit and why it was important. [4 marks]

1. In the summer of 1958 Kilby, working alone in the laboratory at Texas Instruments, tried to solve the problem of connecting growing numbers of transistors, resistors and capacitors without soldering each one separately.
2. He showed that an oscillator's different components could all be made from a single piece of semiconductor material.
3. In September 1958 he built a complete working circuit in one piece of germanium and filed a patent for his "Miniaturized Electronic Circuits" in February 1959.
4. This integrated circuit, or chip, became the basis of almost all later computers and electronic devices, since it allowed many components to be connected on a single block without hand-soldering.

Q5. Explain how the double heterostructure laser works, and discuss how this invention changed technology. [6 marks]

1. A double heterostructure laser has a very thin layer with a small band gap sandwiched between two layers with a larger band gap, a design proposed independently by Alferov and Kroemer in 1963.
2. Electrons and holes that recombine inside the thin middle layer release energy as photons, which are the particles of light that make up laser light.
3. Because the thin middle layer traps both the electrons and holes and the photons they produce, the density of excited carriers rises much higher than in a simple, single-material laser.
4. This confinement lets the laser run continuously at room temperature instead of needing bulky cooling and only working in short pulses, as earlier semiconductor lasers did.
5. Alferov's group achieved a pulsed version of this laser in late 1968 and a continuously operating version at room temperature in May 1970, ahead of competing groups in the United States.
6. Without this invention, the Academy noted, modern society would lack optical-fibre broadband communication, CD players, laser printers, bar-code readers and laser pointers, all of which rely on heterostructure laser diodes.

Q6. Why did the Nobel committee treat the integrated circuit and semiconductor heterostructures as part of the same prize? [3 marks]

1. Both inventions were judged to be foundational to modern information and communication technology, which needs electronic systems that are both fast and small.
2. The integrated circuit solved the problem of fitting huge numbers of components together without error-prone soldering, enabling computers and processors.
3. Heterostructures solved the separate problem of speed, enabling fast transistors and continuous-working lasers that carry information through satellites, mobile networks and optical fibres.

Key takeaways

• The Nobel Prize in Physics 2000 honoured work on information and communication technology, split between heterostructures and the integrated circuit.
• Zhores Alferov and Herbert Kroemer each received one quarter of the prize for semiconductor heterostructures used in high-speed and opto-electronics.
• Jack Kilby received one half of the prize for his part in inventing the integrated circuit at Texas Instruments in 1958.
• A heterostructure is built from thin layers of semiconductor materials with different band gaps, stacked on top of each other.
• Heterojunction transistors made possible the fast, low-noise amplifiers used in mobile phone networks and satellite links.
• Double heterostructure lasers, proposed in 1963, made it possible for semiconductor lasers to work continuously at room temperature.
• Alferov's team achieved continuous room-temperature laser operation in May 1970, a few weeks before competing American groups.
• The integrated circuit let many transistors, resistors and capacitors be built on one chip instead of being hand-soldered together.

Test yourself

Who shared the Nobel Prize in Physics 2000 with Jack S. Kilby?

Zhores I. Alferov and Herbert Kroemer shared the other half of the prize for developing semiconductor heterostructures used in high-speed and opto-electronics.

What share of the prize did Jack Kilby receive?

Jack S. Kilby received one half of the Nobel Prize in Physics 2000, while Alferov and Kroemer each received one quarter.

Where was Zhores Alferov affiliated at the time of the award?

Zhores Alferov worked at the A.F. Ioffe Physico-Technical Institute in St. Petersburg, Russia, where he had been director since 1987.

What is a semiconductor heterostructure?

A semiconductor heterostructure is built from several thin layers of different semiconductor materials, each with a different band gap, stacked on top of one another.

What problem in electronics did Kilby's integrated circuit solve?

It solved the problem of connecting many transistors, resistors and capacitors without error-prone hand-soldering, by building them all on one semiconductor chip.

Why could double heterostructure lasers work continuously at room temperature?

They confined electrons, holes and photons together in one thin layer with a smaller band gap, raising their density enough for continuous laser action without extra cooling.

When was the Nobel Prize in Physics 2000 announced, and by whom?

It was announced on 10 October 2000 by the Royal Swedish Academy of Sciences.

Give one everyday device mentioned by the Academy that depends on heterostructure lasers.

CD players use heterostructure laser diodes to read data, and bar-code readers and laser pointers use similar technology.