INVERSION OF DOSE-RATE EFFECTS IN ION-IMPLANTED GALLIUM-ARSENIDE IN THE LOW-DOSE REGIME

Control of threshold voltage during gallium arsenide (GaAs) Metal Semi conductor Field Effect Transistor (MESFET) processing is critical. Var iation in the dose rate during ion implantation has previously been de monstrated to affect sheet resistance and peak damage fraction for dos es of 5 x 10(13) ions/cm(2) and higher. In this high dose regime, shee t resistance and damage increase as the dose rate increases. This pape r describes dose rate effects in the low dose regime, where traditiona l channel implants are done, i.e., for Si-29(+) in the low 10(12) ions /cm(2) range. Si-29(+) was implanted at 3 X 10(12) ions/cm(2) followed by a co-implant of Be-9(+) at 1 X 10(12) ions/cm(2) into GaAs substra tes. The silicon dose rate was varied from 3 nA/cm(2) to 44 nA/cm(2). The FET channel resistance varied by 4.0%, and was a direct function o f the implanted beam current. Sheet resistance decreased as the beam c urrent increased, which is in sharp contrast to results previously pub lished for the high dose regime. Damage has been characterized and cor related to the electrical properties in the low dose regime. The resul ts are compared to those for the high dose regime in order to more cle arly define the differences associated with the inversion of the dose rate dependence between the low dose and high dose regimes.