Research On Characteristics Of Germanium And Metal-Doped Germanium Films Deposited By Magnetron Sputtering

Thanks to excellent optical electrical characteristics, crystalline germanium has been successfully used in non-volatile memory and integrated optoelectronics. Doped magnetic semiconductors have attracted great attention for their applications in spintronics devices. Transition metal-doped Ge thin films are potential candidates of as semiconductor materials as well as the potential compatibility with current Si-based technology. Therefore, it is valuable to study the preparation of metal-doped Ge thin films for raveling the real mechanism of the magnetism, finding new structure characteristics and exploring higher Curie temperature.First, Ge thin films are deposited on Si (100) substrate by means of direct current (DC) reactive magnetron sputtering and the optimal deposition conditions are obtained by changing the experimental parameters. The optimal growth conditions are the sputtering power of80W, deposition time of2h, substrate temperature of500℃, and gas pressure of1.6Pa. It is indicated from X-ray diffraction (XRD) spectra that the Ge thin film demonstrates (220) preferred orientation. The results of Raman spectra are consistent with XRD. SEM measurements show that the compact surface structure composed by approximate rounded crystal particles is obtained for Ge thin films. It is observed that the reflectivity of the film increases first and then decreases with the increase of the sputtering pressure by UV-VIS-NIR spectrophotometer. Secondly, the MnxGe1-x(x=0.02,0.05,0.1,0.3) thin films are deposited on Si (100) substrates by DC reactive magnetron sputtering. XRD results indicate that the crystal direction of MnxGe1-x films is agree with Ge films and no other diffraction peaks for Mn or other impurities such as Mn, Mn-Ge is observed. It is suggested that Mn atoms are incorporated into the Ge lattice. The MnxGe1-x (x=0.02,0.05) thin films demonstrated (220) preferred orientation yet comparing to Ge thin films, but the preferred orientation of the MnxGe1-x(x=0.1,0.3) thin films transforms from (220) to (111). Vibrating sample magnetometer (VSM) measurements indicate that the room-temperature ferromagnetism is attained and the saturation magnetization increases first and then decreases with the increase of Mn doping concentration. The maximal saturation magnetization of0.54emu/cm3is obtained at the Mn concentration of10%, but the saturation magnetization decreases while the Mn concentration is increased to30%.Finally, Co-doped MnxGe1-x thin films are deposited on Si (100) substrates by magnetron sputtering. The study of XRD patterns indicates that Co (20W)-doped MnxGe1-x thin films only show Ge cubic crystal structure, and the intensity of a diffraction peak of Co (80W)-doped MnxGe1-x thin films is weaker. Raman spectra show that Co (20W)-doped MnxGe1-x thin films have strong diffraction peaks that are in agreement with XRD results. The apparent deviation of peak locations of the Co (80W)-doped MnxGe1-x thin films are attributed to the lower crystallinity. At the same time, the composition of the film is determined by an energy disperse X-ray (EDX) analyzer. The test result revealed that the Co contents are3.34%,51.2%for Co(20W) and Co(80W)-doped MnxGe1-x thin films, respectively. It is indicated from SEM images that the films have compact surface structure and the root-mean-square (RMS) roughness of the Co (80W)-doped MnxGe1-x thin film is larger than the Co(20 W)-doped MnxGe1-x thin. It is revealed by VSM that Co (20W) and Co (80W)-doped MnxGe1-x thin films exhibit the room temperature ferromagnetism.