Formation of GaAs Ohmic Contacts by using Ion Beam Mixing
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In this work, we have chosen to study Pt/GaAs system which is already being used successfully in GaAs integrated circuit to form gate electrodes by using its characteristic solid phase reaction at low temperature [3], and Ge/GaAs system which recently attracts attentions as non-metal ohmic contacts. We observed alloying and recrystallization enhancements induced by ion beam mixing and checked the formation of ohmic contacts in these systems. Mat. Res. Soc. Symp. Proc. Vol. 54. c1986 Materials Research Society
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ION BEAM MIXING IN Pt/GaAs SYSTEM Sample preparation Pt films (55nm) were evaporated onto chemically cleaned Cr-doped semiinsulating GaAs substrates using an electron beam evaporation method. 7 of 160 KeV were implanted through the Pt layer to a dose of l.OE16 cm at room temperature. The energy was so chosen that the projected rlnqe was+ nearly equal to the thickness of the evaporated Pt films. The Ar and Ge implanted samples were also prepared. The methods were the same as mentioned above for Si mixing, except the thicknesses of Pt films. 45nm and 25 nm thicknesses were chosen to be equal to the projecqed rangTs of implantea
with 160 FeV into Pt films, for imnplanted ions Ar
and Ge
respectively.
Alloying by ion beam mixing Figure 1 shows the 2.3 MeV He backscattering spectra of Si+ and Ar+ implanted sampleq. By comparing the spectrum of the Pt as-deposited sample with those of Si and Ar implanted samples, it can be concluded that alloying by ion beam mixing hasoccured at room temperature. The measure of the alloying phenomenon is estimated here by the thickness of the GaAs layer consumed by the alloyed layer.. From the width of the amount of alloying is calculated to be 25 nm, which is corresponding to the value obtained by thermal annealing at 300% for 40 min. When the unimplanted sample was annealed at 420*C for 30 min, the solid phase reaction between Pt and GaAs was completely carried out. The amount of GaAs reacted in this case was about 100 nm, which was about twice of the thickness of the initially evaporated Pt. P' b) a) P' !220
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alcas a wheRutherford backscattering specth a showingsalloying reaction in the anuipatdsml.aentemlyanae.Mroealy Pt/GaAs system by Si+(a) and Ar+(b) ion beam mixing. By adding the thermal annealing process after implantation, it was found that alloying proceeded further, at a speed which annealed. teerate assamethealloycase when an unimplanted sample had been thermally was Moreover, ed layers prepared by such processes were stable even at 8000C for 30 min annealing with SiO, encapsulation for both ion beam assisted and/or thermal annealing proce ses. Figure 2 shows comparisons for the amount of GaAs reacted with Pt by ion beam mixing and therm
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