Israeli scientists have set a new world record for semiconductor purity, breaking one set eight years ago in the US.
Researchers at the Condensed Matter Physics Department of the Behovot-based Weizmann Institute of Science have developed crystals of gallium arsenide so pure that electrons can traverse the material at a rate of 14.4 million cm per second. The previous 11.7 million cm/s record was achieved by AT&T and Bell Laboratories.
In the long term, the discovery could have implications for the efficiency of top-of-the-range semiconductors using gallium arsenide rather than the more common silicon. Everyday products already using the material include cellular phones and CD players.
Achieving higher and higher levels of semiconductor purity is one of the main problems taxing research laboratories as they work towards the next generation of designs. Impurities lead to collisions that deflect electrons and decrease their speed, a phenomenon referred to as scattering.
However, Weizmann’s results are today mostly of scientific and research value, as Professor Mordehai Heiblum, the project’s lead researcher acknowledges.
‘There are no direct applications for this technology today, because all existing devices work at room temperature. At room temperature, there is a large lattice vibration which inhibits free electron motion. Our results are for low temperatures where the vibrations cease and any impurities are the dominant factor in scattering,’ he says. ‘However, if, in the future, industry chooses to use cool transistors, this work will take on greater commercial importance.’
Weizmann and the research’s other backers – the Israel Academy of Sciences and Humanities, Austria’s Ministry of Science, the Robert Bosch Foundation and the Israeli Ministry of Defence – are making details of the processes they have used freely available, rather than treating their findings as proprietary technology.
The gallium arsenide crystals were grown using a chamber operating at a near-perfect vacuum rate of 10-16 atmospheres, the lowest currently available.
Within the system, vacuum pumps operated at -268 degrees C, but the crystals themselves were produced at an oven temperature of 650 degrees C.
Thanks to the near-vacuum and temperature differential, the resulting crystals were so pure that they contained only one foreign atom per five billion gallium atoms. Weizmann says this would be the equivalent of one sugar cube in a five-storey building on a 300m2 site.
The record-breaking measurements were achieved by testing the time taken for an electron to move through 1cm of crystal in an electric field of 1V per cm at a temperature of 0.1 degrees K (one tenth of a degree above Absolute Zero).
A fuller account of how the Weizmann scientists achieved their results appears in latest edition of the academic journal Applied Physics Letters.