The Dependence of Electrical and Optical Properties of RF Sputtered Amorphous Silicon–Carbon Alloy Thin Films on Substrate Temperature and Hydrogen Flow Rate

Abstract

The dependence of optical band gap Eg and room temperature dark dc conductivity σDRT of rf‐sputtered a‐SiC: H films on substrate temperature Ts and hydrogen flow rate is investigated. For a given hydrogen flow rate, the optical band gap Eg is found to increase as Ts increase up to a critical value, and then decrease upon further increase of Ts. σDRT is found to decrease by about three orders of magnitude as Ts increases, reaching a minimum at 160 and 120 °C for flow rates of 9 and 20 scc, respectively. The conductivity activation energy Ea reaches a maximum, respectively, at the above substrate temperatures. Changes in the hydrogen flow rate from 9 to 20 scc result in an overall increase of the optical band gap by about 0.5 eV, while σDRT decreases by two orders of magnitude. For both hydrogen flow rates, 9 and 20 scc, the Meyer‐Neldel rule is found to hold.

The a‐SiC/c‐Si(n) Isotype Heterojunction as a High Sensitivity Temperature Sensor

“…This suggests that compared with E, the quantity (1-1/n)qV can be ignored, in this range of reverse bias voltages. The observed value of E(0.36e 1/) is exactly equal to the sum of the a-SiC conductivity activation energy (= 0.18el0 [17] and the heterojunction barrier height AEe-Vb-VI('O.18eV), suggesting that our previous assumption for E is correct.…”

Electrical properties of annealed a-SiC:H thin films

“…The deposition rate of the films was 1.2 Å /s and their final thickness ffi1 lm. Under these deposition conditions the dangling bonds and structural defects of a-SiC:H thin films are compensated to an optimum degree as we have found in a previous work [7], leading to an optimization of electrical and optical properties of a-SiC:H.…”

“…The optimization of the properties of the above devices has been mainly focused on the improvement of a-SiC:H quality and, more specifically, to the decrease of dangling bonds and structural defects in the amorphous material. This has been achieved by changing the deposition parameters [6,7] and by varying the atomic ratio C/ Si [6]. Further improvement of a-SiC:H quality has been reported by using thermal annealing process in the range from 723 up to 923 K [8][9][10][11][12].…”

“…The present work is a contribution to this particular direction and, more specifically, it is studied the effect of annealing process, in the temperature range from 573 up to 1048 K, on the electrical properties of a-SiC:H. The experimental results have shown that the density of localized gap states at the Fermi level, N(E F ), presents the minimum value at T a = 873 K, whereas the activation energy of dc conductivity, E a presents the maximum value. Since in the present work the a-SiC:H thin films are undoped, the increase of E a with T a (up to 873 K) reveals decrease of gap states due to higher compensation degree of dangling bonds and structural defects in the films [6] and, consequently, the maximum value of E a at T a = 873 K suggests the optimum material quality [6,7,13]. …”

Study of optical sensors of the form A l/a-SiC:H/c-Si(n) with high sensitivity

“…Depending on the preparation technique or on deposition conditions the properties of a-SiC:H can be modified so that a suitable combination that requires each application can be achieved. The high absorption in the blue region of the visible spectrum is very attractive for manufacturing optical sensors using a-SiC:H. Even though the optimization of such optical sensors has been mainly focused on the improvement of optoelectronic properties of a-SiC:H thin films by using different preparation technique or by changing deposition conditions [8][9][10][11][12], very few works studied further quality improvement of aSiC:H by thermal annealing [13,14]. On the other hand, although a-SiC:H is an interesting material for photosensing applications in the low wavelength and UV range of the spectrum, very few works have been published on the optoelectronic properties of Metal/a-SiC:H Schottky diodes [8,15].…”