Study gets good dope on fast germanium transistors

Phosphorus atoms self-organise into a germanium layer
Tuesday, 14 August, 2012
Bob Beale

The next generation of high-speed transistors based on germanium - rather than the familiar silicon - has moved closer with new research revealing how individual phosphorus atoms can be predictably incorporated and self-organise into a germanium layer.

Adding extra atoms to semiconductors to provide free carriers for conducting an electrical current, a process known as doping, is the key to making germanium transistors available for the development of novel high-speed electronic components, notably for computing  and  fast optical interconnects.

Writing in the journal Physical Review Letters, Dr Giordano Scappucci and co-workers from UNSW, the University of Sydney, and Universita’ di Roma Tre have demonstrated a new method to densely pack dopant molecules in a layer on a germanium surface.

As observed with a scanning tunneling microscope, that layer then self-organises to form molecular patterns with one phosphorus dopant atom for every two germanium atoms, the researchers report. The method was confirmed by theoretical calculations.

Doping germanium at high concentrations to make it highly conductive is the subject of intense research around the world, because it lies at the heart of novel developments in integrated silicon-compatible lasers and quantum information processing devices.

“The first transistors in the 1940s were actually made of germanium, before Texas Instruments produced the first commercial ones in silicon in the 1950s, but now there’s renewed interest in germanium,” says Dr Scappucci, a Senior Research Fellow at the UNSW School of Physics.

“Germanium has similar properties to silicon and has great potential for high-speed devices because it can achieve higher switching speeds than silicon, which will enable faster chips containing smaller transistors.

 “There is an international race both in industry and research labs with the aim of developing a reliable doping technology for germanium . This new atomic-scale insight provides crucial information for the future development of stable and efficient doping processes in germanium based electronics.

“It helps pave the way for the next generation of high-speed transistors, complementary metal-oxide-semiconductor–compatible integrated lasers and germanium devices fabricated at atomic level.”

Dr Scappucci received a 2012 UNSW GoldStar Award for a research project related to the paper.

Media contacts:

Giordano Scappucci -  02 9385 4960 or  0406 952 915

UNSW media liaison – Bob Beale 0411 705 435