An amorphous dielectric-to-amorphous semiconductor transition in hydrogenated carbon-germanium films

Abstract

Electronic properties of a-GexCy:H films plasma-deposited in a new type of audiofrequency reactor with three parallel electrodes have been investigated. It has been found that small changes in coupling capacity in the reactor can cause a drastic step change in the electronic structure of the deposited films. This effect is attributed to a transition from amorphous dielectric to amorphous semiconductor.

Mesostructured thin films deposited by PECVD from TMGe

“…The dramatic change of electrical conductivity at V (À) = 450 V is related to transition from a-I to a-S electronic structure [6]. It is interesting to notice that not only activation energy E A changes rapidly at that point but also pre-exponential factor r 0 increases about four orders of magnitude, which must be involved by step transition in charge transport mechanism.…”

“…Depending on the energy of ions bombarding the surface of growing material, films characterized as amorphous semiconductors (a-S) and amorphous insulators (a-I) can be fabricated from tetramethylgermane (TMGe) [6]. The transition between these two material structures is very sharp and results in dramatic change of electrical properties, e.g.…”

Transition from amorphous semiconductor to amorphous insulator in hydrogenated carbon–germanium films investigated by IR spectroscopy

“…The capacitance controls the negative amplitude V (À) of the voltage with respect to the ground electrode and in consequence energy of ions bombarding the small electrode [4]. The negative amplitude V (À) , was the only variable parameter in this study and could be changed in the range 0-1200 V. For values of V (À) < 450 V and V (À) > 450 V materials ranking among amorphous insulator (a-I) and amorphous semiconductor (a-S) were produced respectively [1,2]. The flow rate and initial pressure were 11 sccm and 13 Pa, respectively.…”

“…Changing only the energy of ions bombarding surface of the growing layer, two distinct materials, namely amorphous insulator (a-I) and amorphous semiconductor (a-S), can be produced from single precursors (e.g. tetramethylgermane -TMGe) [1,2]. The differences between a-S and a-I films can be illustrated by a comparison of values: specific electrical conductivity (10 À4 S/m and 10 À18 S/m) [3], transport gap (0.3 eV and 0.9 eV) [2] and optical gap (2 eV and 3.2 eV) [1].…”

“…tetramethylgermane -TMGe) [1,2]. The differences between a-S and a-I films can be illustrated by a comparison of values: specific electrical conductivity (10 À4 S/m and 10 À18 S/m) [3], transport gap (0.3 eV and 0.9 eV) [2] and optical gap (2 eV and 3.2 eV) [1]. This spectacular change of electronic structure can be caused by a small variation of plasma deposition parameters that are responsible for the impact energy of ions bombarding surface of the growing film [4].…”