High-purity semi-insulating GaAs material for monolithic microwave integrated circuits

Liquid-Encapsulated Czochralski (LEC) growth of large-diameter bulk GaAs crystals from pyrolytic boron nitride (PBN) crucibles has been shown to yield high crystal purity, stable high resistivities, and predictable direct ion-implantation characteristics. Undoped (≲low 10
¹⁴
cm
^-3
chromium) and lightly Cr-doped (low 10
¹⁵
cm
^-3
range) -GaAs crystals, synthesized and pulled from PBN crucibles contain residual shallow donor impurities typically in the mid 10
¹⁴
cm
^-3
, exhibit bulk resistivities above 10
⁷
Ω . cm, and maintain the high sheet resistances required for IC fabrication (>10
⁶
Ω/□) after implantation anneal. Direct
²⁹
Si channel implants exhibit uniform (± 5 percent) and predictable LSS profiles, high donor activation (75 percent), and 4800- to 5000-cm
²
/V . s mobility at the (1 to 1.5) × 10
¹⁷
cm
^-3
peak doping utilized for power FET's. It has also been established that LEC crystals can provide the large-area, round (100)-substrates which will be required to realize a reproducible, low-breakage GaAs IC processing technology. The fabrication of 2-indiameter GaAs substrates to tight dimensional tolerances, with (1 10)-orientation flats and edge rounding has been demonstrated experimentally.