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Lucent Technologies Use Ion Implantation And MBE To Solve 30-Year-Old Problem Of How To Make GaAs MOSFETs

SAN FRANCISCO, Dec. 10 /PRNewswire/ -- A group of researchers from Lucent Technologies (NYSE: LU) announced today that they have solved a problem that has puzzled researchers for 30 years -- how to create GaAs metal oxide semiconductor field effect transistors (GaAs MOSFETs).

In a paper presented to the International Electron Devices Meeting (IEDM) here, a research team led by Ming-Hwei Hong and Fan Ren of Bell Laboratories, the research and development arm of Lucent Technologies, disclosed that it succeeded in depositing a special formulation of gallium oxide (Ga2O3) as the gate dielectric on a GaAs semi-insulating substrate to fabricate both p-channel and n-channel GaAs MOSFETs.

"We have successfully demonstrated the first enhancement-mode GaAs MOSFET with an inversion channel," Hong said, "by combining ion implantation and oxide deposition processes. This promises to make GaAs MOSFET devices very attractive for a variety of applications because we are using mainstream GaAs technology that currently is being used by the industry to make GaAs metal- semiconductor field-effect transistors (MESFETs). One obvious application of GaAs MOSFET devices could be for mobile wireless communications."

GaAs-based transistors and circuits are used in a variety of communications applications because -- in comparison to Si-based devices -- they operate at higher frequencies with lower power than silicon devices and, because of their semi-insulation substrates, it is easier to design circuits without undesirable parasitic characteristics that degrade performance.

Today, most GaAs-based integrated circuits require double supply voltages and have relatively high power consumption. This results in shorter battery life and more complex circuitry in battery-powered applications, such as wireless personal communications systems. In contrast, silicon-based MOSFET semiconductors, a mature technology, are more simple in design and use less power, though they operate at lower frequencies.

For more than three decades, researchers have been trying to develop a way to make GaAs-based MOSFETs, in order to take advantage of the properties of GaAs. Numerous attempts with anodic, thermal, and plasma oxidation and deposition of various dielectric materials have been used to passivate the GaAs surface. However, until last week -- when the Bell Labs team succeeded in its proof-of-concept demonstration -- efforts to make viable devices eluded researchers due to, among other things, the poor quality of the interface between the gate oxide and the GaAs substrate.

In the silicon oxide-to-silicon (SiO2-to-Si) gate-to-substrate, the interfaced state density of the two materials is about 10(10) cm-2 eV-1. making it ideal for the direct current (dc) and low-frequency operation of the Si devices. In contrast, researchers in the past found it very difficult to match the densities of Si devices when interfacing oxides to the GaAs substrate. This resulted in poorly operating devices.

"Oxidation of gallium arsenide doesn't make a good oxide," Hong said, "but we have solved this problem by using ion implantation and MBE to deposit a special formulation, which is basically Ga2O3, on to the GaAs substrate. With this formulation, we have been able to create a Ga2O3-to-GaAs interface with a state density in the low 10(10) cm-2 eV-1. We've solved the interface problem at last!"

Potential applications of GaAs MOSFETs include:

-- Low-cost, high-efficiency personal communications system (PCS) transmitter-receivers;

-- High-performance (low noise), high-efficiency power amplifiers for terminals and base stations;

-- Integrated radio frequency (RF) and mixed-mode circuits;

-- High-speed, low-power digital processors; and

-- Seamless integration with current commercial high-electron-mobility transistors (HEMTs) and GaAs MESFETs, which are being used as work horses in cellular and PCS phones and in direct broadcast satellite receivers.

"There is much more work to be done before such applications become a reality," Hong cautioned, "but the potential is there."

The use of MBE to make electrical and optoelectrical devices was pioneered at Bell Labs by Alfred Y. Cho, now director of semiconductor materials research at Bell Labs in Murray Hill, N.J.

According to Young-Kai Chen, head of the high-speed electronics research department in the wireless communications lab at Bell Labs, "We have been able to take advantage of our 25 years of experience in MBE fabrication, and the use of low cost commercially available ion implantation technology, to solve one of the thorniest problems in III-V materials fabrication. We're very happy about our results and we hope Bell Labs has made a valuable contribution to Lucent Technologies' leadership in semiconductor applications."

In addition to Hong and Ren, the research team that solved the puzzle include Cho, Chen, Bill Hobson, Jenn-Ming Kuo, Raynien Kwo, Jim Lothian, and Joe Mannaerts, all of Bell Labs in Murray Hill.

Lucent Technologies (NYSE: LU) designs, builds, and delivers a wide range of public and private networks, communications systems and software, consumer and business telephone systems, and microelectronics components. Lucent Technologies was formed as a result of AT&T's restructuring and became a fully independent company -- separate from AT&T -- on Sept. 30, 1996.

(Additional technical information is available at Lucent Technologies' website:\press\)

SOURCE Lucent Technologies
 -0- 12/10/96

/CONTACT: George Moffatt of Bell Laboratories, office, 908-582-4815, or home, 908-544-1726 , or; or Richard Muldoon of Bell Laboratories, office, 908-582-5330, or home, 201-636-6699, or


CO: Lucent Technologies ST: New Jersey, California IN: TLS SU:

MM-TM -- NYTU088 -- 5616 12/10/96 14:04 EST
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Date:Dec 10, 1996
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