Structure change and resistivity step of evaporated Ge films in dependence on the substrate temperature

Abstract

Results are reported of an investigation of the electrical properties of Ge films evaporated on Duran glass at different substrate temperatures TS. The resistivity measurements allow to distinguish between amorphous and polycrystalline films on account of a steep resistivity step of four or seven orders of magnitude at 294 or 80 K lattice temperature, respectively as found at TST = 135°C. This step is due to the fact that with the relatively high evaporation rate used, grains of only equal size are performed, and that with decreasing TS at TST all grains fall below a critical grain size. By the analysis of the lattice temperature dependence of the resistivity of the polycrystalline films, making use of the mean free path of carriers between two collisions at grain boundaries, the critical grain size was found to be about an elementary cell.

Different Proportions of a-Ge and c-Ge in Dependence on the Substrate Temperature of Evaporated Films Determined by Refractive Index Analysis

“…2 in dependence on the substrate temperatures T, At a first regard it is very surprising to find a step-wise change of the a-Ge fraction of just 50 to -l O O~o around TsT in going to lower substrate temperatures. But, from [2] we have seen that the crystalline particle size for our films decreases with decreasing T , , the limiting value being reached a t T s = 140 "C. I n connection with the results of [2] it can be said that this T , reflects a critical grain size of 5 A for which crystdine clusters are even performed and, on the other hand a critical temperature below which the a-proportion increases steeply above 50%.…”

“…The kind of configuration within the films is generally examined by X-ray and electron diffraction patterns. I n a n earlier paper [2] we pointed out the possibility of finding and assigning an amorphous and a polycrystalline region by measurements of electrical resistivity of the Ge thin films.…”

The amorphous–crystalline transition in germanium films

“…I n these two cases the transition temperature lies within 10 K from our observation. I n [7] the substrate temperature is measured prior to deposition by thermocouple in contact with the front surface of the substrate. In our opinion this method leads to too low substrate temperature, In the first place, because it is measured on the front surface and, secondly, because heating from the source is not considered.…”

Plasma Resonance in Heavily Doped Germanium Thin Films

“…1, upper part.) due to the c a r r i e r scattering at grain boundaries(8). Thus, contrary to the undoped films the mobility in the Al-doped films is mainly influenced by scattering at ionized impurities.…”

“…of should differ from that of bulk Ge in accordance to refractive index L Films were prepared by evaporation of intrinsic germanium on glass substrates (substrate temperature 350 OC) at a rate of 380 g/s and a pressure of Such germanium films a r e polycrystalline and indicate p-type conduction (7,8) with a high concentration of acceptors introduced into the film by grain boundaries mainly influencing the total mobility (8). Since these acceptors a r e placed only at the grain boundaries but a r e not distributed homogeneously in the sample, the films were doped additionally by aluminum in order to reach much higher and homogeneous p-concentrations.…”