Large Diameter, Undoped Semi-Insulating GaAs for High Mobility Direct Ion Implanted FET Technology

  • R. N. Thomas
  • H. M. Hobgood
  • D. L. Barrett
  • G. W. Eldridge


The growth of 2 and 3 inch diameter, <100> oriented semi-insulating GaAs crystals of improved purity by liquid encapsulated Czochralski (LEC) growth from silicon-free, pyrolytic boron nitride (PBN) crucibles in a high pressure Melbourn crystal puller, is described. Undoped and Cr-doped LEC GaAs crystals pulled from PBN crucibles exhibit bulk resistivities in the 107–108 and 108–109 ohm-cm ranges, respectively. High sensitivity SIMS demonstrates that GaAs crystals grown from PBN crucibles contain residual silicon concentrations in the low 1015 cm-3 range, compared to concentrations up to the 1016 cm-3 range for growths in silica containers. The residual chromium content in LEC/PBN-grown crystals is below the l05 cm-3 range.

The achievement of direct ion implanted channel layers of near-theoretical mobilities is further evidence of the improved purity of undoped, semi-insulating GaAs prepared by LEC/PBN crucible techniques. Direct implant FET channels with 1–1.5 × 1017 cm-3 peak donor concentrations exhibit channel mobilities of 4800 to 5000 cm2 V-1 s-1 in undoped, semi-insulating GaAs substrates, compared with mobilities ranging from 3700 to 4500 cm2 V-1 s-1 for various Cr-doped GaAs substrates. Discrete power FETs, which exhibit 0.7 W mm-1 output and 6 dB associated gain at 8 GHz, have been fabricated using these implanted high mobility, semi-insulating GaAs substrates.


GaAs Substrate GaAs Crystal Boric Oxide Liquid Encapsulate Czochralski Pyrolytic Boron Nitride 
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Copyright information

© R.N. Thomas, H.M. Hobgood, D.L. Barrett and G.W. Eldridge 1980

Authors and Affiliations

  • R. N. Thomas
    • 1
  • H. M. Hobgood
    • 1
  • D. L. Barrett
    • 1
  • G. W. Eldridge
    • 1
  1. 1.Westinghouse Research and Development CenterPittsburghUSA

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