Effects of temperature and near-substrate plasma density on the structural and electrical properties of dc sputtered germanium thin films

Abstract

Germanium thin films were deposited by dc reactive magnetron sputtering as a function of substrate temperature and ion flux using an unbalanced magnetron with an external magnetic field. The ion flux and energy distribution were measured using a retarding field energy analyzer (RFEA), a flat probe with a guard ring, and cylindrical Langmuir probes. The RFEA ion flux, the flat probe saturation currents, and the ion densities inferred from the cylindrical probe data are in very good agreement over a wide range of plasma densities, which were varied both by the external coil current and discharge power. The RFEA ion energy distributions are in good agreement with the plasma potentials inferred from the cylindrical probes, and suggest that the nonuniformity of the plasma in the vicinity of the substrate holder should be considered in the interpretation of probe results in these systems. The deposited films were characterized by x-ray diffraction, Raman spectroscopy, optical transmission, resistivity, and Hall effect measurements. Under low ion bombardment conditions, an abrupt onset of the crystalline phase with respect to temperature is observed in the Raman and x-ray diffraction measurements, and the crystal quality increases with increasing temperature above the transition temperature. The transition is also accompanied by a sharp decrease in film resistivity. The microcrystalline films have a strong preferential orientation in the (220) direction, and are p type with carrier densities in the range 1018 cm−3 and mobilities in the range 15–30 cm2/V-s. The structural and electronic properties of the films are sensitive to the ion flux. Near the transition temperature the effects of increasing ion flux can be attributed to the small temperature rise that accompanies the higher plasma density. At higher temperatures the increased ion flux results in a more random crystallographic orientation, with significantly lower carrier concentrations and only slightly lower carrier mobilities, implying either a reduction in acceptor defect density and/or the creation of compensating n-type defects.

Influence of plasma-generated negative oxygen ion impingement on magnetron sputtered amorphous SiO2 thin films during growth at low temperatures

“…[1][2][3][4][5][6]. This technique is one of the most popular in science and technology due to the high quality of the deposited films, the possibility to work on large substrates as well as to the high deposition rates achieved.…”

Low‐temperature deposition of polycrystalline germanium on silicon by magnetron sputtering

“…The sputtering of the ultra‐thin Si layer on the Si wafer is for the purpose of presenting a surface conducive for the subsequent growth of Ge. Prior studies on Ge sputter deposition have indicated that the underlying surface can create a difference in the nucleation dynamics of Ge [5]. The ultra‐thin Si layer can function as a nucleation layer for the subsequent Ge deposition.…”

“…In the absence of the ultra‐thin Si intermediate layer, the spectrum does not show any peaks pertaining to polycrystalline Ge. A rather broad diffraction peak is barely discernible around 2 θ of 25°, which can be attributed to a fully amorphous structure [5]. In the case of Ge film deposited on Si wafer at the same process temperature with an ultra‐thin intermediate Si layer, diffraction peaks are clearly visible at 2 θ values around 27.3° and 45.3° and 53.7°.…”