semiconductor can be made magnetic by doping it with impurity such as manganese (Mn). The resulting material is commonly known as a dilute magnetic semiconductor (DMS). The DMS combines the properties of magnetism used in permanent information storage with that of
semiconductor memory and logic devices to develop new electronic devices known as DMS spintronics. This could offer opportunities to develop a new generation of devices that are nonvolatile, have high data processing speed, large integration capabilities and lower power consumption than conventional devices.
Silicon (Si) is best known as the semiconductor material to make integrated circuit chips. Recently, it has been reported in the literature that Si can be "ferromagnetic" (FM) or permanently magnetic well above room temperature by Mn implantation upto a concentration of 1% per atom. This has great potential impact on the development of spintronic devices which use Si endowed with magnetic properties. On the other hand, since Si1-xGexis a promising material for future CMOS technology, the possibility of Mn doping Si1-xGexmight also open a new route to realize the integration of magnetic semiconductors into Si based devices. Hence, one of the current research areas is to synthesize a Si1-xGex high temperature FM property.
We note that ion implantation is useful to screen particular combinations of magnetic dopants and host semiconductors for their ferromagnetic properties, and this may have applications in forming selected area contact regions for spin-polarized carrier injection in device structures. Thus, we employed this method to synthesize Mn-doped Si1-xGex. Two different dosages of Mn ions (1x1016 and 2x1016/cm2) were implanted at 300ºK into the relaxed Si0.75Gexlayers that were grown on Si(100) substrates. X-ray photoelectron spectroscopy revealed that the Mn peak concentrations were about 8% and 12% for the lower and higher dosages, respectively. Rapid thermal annealing was performed at temperatures between 700ºC to 900ºC for 20s. Raman spectra showed that the as-implanted layers were amorphous and the defects were healed after the annealing.
The hysteresis curves, measured by superconducting quantum interference device (SQUID) magnetometer, showed that the as-implanted and annealed Mn-Si1-xGex were ferromagnetic. It can be observed in Figure 1 that the saturation magnetization increases with increasing annealing temperature; this could be due to the improved crystal qualities and the activation of Mn atoms (substitutional Mn). As shown in Figure 2, the magnetization persists up to 320ºK, and the magnetization increases by a factor of 2 when the Mn dosage was doubled. The hysteresis loops shown in the inset of Figure 2 provide evidence that the samples are indeed ferromagnetic above room temperature. The samples with the higher dosage measured at room temperature exhibit saturation magnetization of about 9 emu/cm3. The corresponding saturation field and coercive field thus obtained are about 1500 Oe and 60 Oe, respectively. The samples were measured to be of p-type (hole) conduction with an effective carrier density of about 2x1019cm-3.
The new observation of ferromagnetic property above room temperature in Si1-xGex is very promising to realize future Si-based “spintronic” devices due to its compatibility with current CMOS technology. This opens up the possibility of its use in devices like personal computers, phones and PDAs.
