Research On The Behavior Of Nickel And Gold In The Single-crystalline Germanium

Compared with silicon, germanium has irreplaceable advantages, it offers a4times higherhole mobility and3higher electron mobility at low-fields. Therefore, germanium has become afocus in recent years. During the germanium crystal growth and wafer preparation, transitionalmetals contamination can easily happen, which always exist as the form of element, complexesand precipitates in germanium. Generally speaking, transitional metals are not conducive to gethigh-quality germanium-based devices. Therefore, it is very important to investigate the behaviorof transitional metals in germanium crystal. In recent years, the rapid thermal processing isnecessary in semiconductor process. Nickel and gold are also the common metals during thegermanium-based devices, and the behavior of nickel and gold in germanium under the rapidthermal processing are still not studied.Thereby, on the basis of reviewing previous studies, amorphous nickel film or gold film wasdeposited on the n-type single-crystalline germanium by the magnetron sputtering. First, theproperties of nickel in germanium under the conventional thermal furnace process and the rapidthermal processing were compared, and the reasons were discussed. The effects of the rapidthermal processing atmosphere, temperature and time on the properties of nickel or gold ingermanium were systematically studied. Moreover, germanium, contained a certainconcentration of nickel or gold after rapid thermal processing, were treated in the conventionalthermal furnace at500oC to study the precipitation behavior of nickel or gold in germanium.The difference of the behavior of nickel in germanium between the conventional thermalfurnace process and the rapid thermal processing were firstly studied. The results showed thatGeNi2was produced under both heat treatments. Under the conventional thermal furnace process,the conductive type of germanium was still n-type, resistivity increased with increasingtemperature. While under the rapid thermal processing, the n-type germanium changed intop-type, resistivity decreased with increasing temperature. The transmittance of germanium was studied by FTIR. The results showed the transmittance decreased after both heat treatments, it isresulted by the GeNi2.The effect of nickel on the conductive type, resistivity, and minority carrier lifetime ofgermanium were measured, processed by the different rapid thermal processing condition,including atmosphere, temperature, and time. Moreover, the diffusion of nickel in germaniumwas studied by spreading-resistance profiling. The results showed it need N2or Ar2during heattreatment to avoid the production of germanium oxide. The n-type germanium changed intop-type due to nickel diffusion, resistivity decreased with increasing temperature or time. Whenthe temperature reached to875oC, resistivity decreased slightly with increasing time. Carrierdensity increased and then decreased with increasing depth, it showed nickel had anout-diffusion behavior in germanium. In addition, the minority carrier lifetime had no relationwith temperature and time. Once processed by the rapid thermal processing, the minority carrierlifetime decreased dramatically to0.1~0.4μs. Germanium contained nickel was still p-type afterthe conventional thermal furnace process at500oC, and the resistivity had basically no change.These might due to the production of shallow acceptor level during the precipitation of nickel ingermanium.The effect of gold on germanium was similar with that of nickel, while the extent was muchlower. The resistivity increased and then decreased with increasing temperature or time due tothe diffusion of gold. The n-type germanium changed into p-type when the temperature reachedto750oC. Carrier density was relatively high near the surface, it rapidly decreased and thenslightly increased with increasing depth. Besides, the minority carrier lifetime of germaniumdecreased with increasing temperature and time. Germanium contained gold was still p-type afterthe conventional thermal furnace process at500oC, and the resistivity gradually increased. Thisshowed that gold precipitated in germanium with a small rate, and the precipitation time constantdecreased with increasing the initial gold concentration in germanium.