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Semiconductor quantum voltage source

Especially interesting for
  • metrology institutes
  • the semiconductor industry

At PTB, a quantized voltage was generated for the first time with an integrated semiconductor circuit. This task was tackled by connecting a single-electron pump and a quantum Hall resistor on a semiconductor chip. So far, such quantized voltages have only been generated by means of superconducting circuits.

Schematic diagram of the semiconductor quantum voltage source. A bove a narrow semiconductor channel, three control electrodes (G1 to G3) are positioned, two of which are controlled by two DC voltages (V1 and V2). Due to the additional AC modulation VAC on electrode G1, the quantized current – which, in turn, generates a quantized voltage Vout in the adjacent quantum Hall resistor – is produced.

Semiconductors have been the most important material system for electronic circuits and IT applications for the past decades. Also in the field of electrical metrology, semiconductors are commonly used to reproduce resistance: due to the quantum Hall effect, the Hall resistance RH is quantized in special semiconducting samples in the magnetic field B. Hereby, its value RH = h/e2 is determined using solely the two fundamental constants h (Planck’s constant) and e (elementary charge). Until recently, it had, however, not been possible to generate a quantized voltage based on semiconducting components. Such quantized voltages could only be realized by means of the Josephson effect, which occurs in superconducting circuits.

In the past few years, semiconductorbased quantized current sources – socalled single-electron pumps – have been developed at PTB. Driven by an alternating voltage of frequency ƒ, these pumps generate a current of quantity I = e ∙ ƒ if a single electron per pump cycle is transported. When combining these singleelectron pumps with a quantum Hall resistor in an integrated semiconducting quantum circuit (see Fig.), one obtains a quantized output voltage of Vout = (h/e) ∙ ƒ. What is particularly interesting about this is that this output voltage is, on principle, identical to the output voltage of a superconducting Josephson circuit but is based on totally different physical effects.

The generation of a quantized voltage using such an integrated semiconducting quantum circuit has recently been demonstrated experimentally. For this purpose, the single-electron pump and the quantum Hall resistor were manufactured in a joint production process from a semiconductor layer system on a chip. To operate the component shown in the picture, only two DC voltages are required, as well as a high-frequency AC voltage to control the single-electron pump. The component exhibits a robust quantization of the output voltage up to frequencies of a few GHz, so that output voltages of up to 10 μV can be generated.

In future, the output voltage of the novel semiconductor quantum voltage source is to be increased even more considerably. The output voltage can, in principle, be increased by a factor of up to 1000 by connecting several single-electron pumps in parallel and by connecting several quantum Hall resistors in series on the semiconductor chip. The quantum voltage having been increased in this way could then be used for fundamental experiments, for example, to close the metrological triangle.


Frank Hohls,
Department 2.5 Semiconductor Physics and Magnetism
phone: +49 (0) 531 592-2410
e-mail: frank.hohls(at)ptb.de