Unexpected properties of the inductively coupled plasma induced defect in germanium

Abstract

Inductively coupled plasma (ICP) etching of germanium introduces a single defect, the E 0.31 electron trap, for a large range of argon partial pressures from 4 × 10 -3 to 6.5 × 10 -4 mbar that correspond to ion energies of 8 to 60 eV. Ge of three crystallographic orientations, (100), (110) and (111), treated with 20 and 60 eV ICP had defect concentration profiles that were similar in appearance, with a maximum concentration of 10 14 cm -3 extending more than a µm into the material, approximately three orders of magnitude deeper than what TRIM simulations predicted. All profiles were measured using Laplace deep level transient spectroscopy (L-DLTS), a technique that is sensitive to defect concentrations as low as 10 11 cm -3 . Isochronal annealing of samples showed concentration curves broadening after a 400 K anneal and decreasing to the 10 13 cm -3 level after a 450 K anneal. Unannealed samples measured after a year exhibited similar decreases in defect concentration without broadening of their profiles. A 550 K anneal lowered the defect concentration to levels below the L-DLTS detection limit. Thereafter additional plasma treatment of the surface failed to reintroduce this defect indicating that the structure required for the formation of E 0.31 was no longer present in the region under observation.

Long range annealing of defects in germanium by low energy plasma ions

“…We should also note that ILMs can not only anneal defects but they can also create or transform them as described in the experiment reported here but also in Ref. [16], where a new defect, known as E 0.31 was created deep into Ge by 8-60 eV ICP Ar plasma.…”

“…1) Dislocations could be introduced by alpha damage but not by the plasma treatment being used as the energy was too low [16]. Also the alpha particle dose was too low to produce multivacancies [17,18] 2) Low energy argon impacts may produce minority charge carriers which are known to anneal out defects near the surface.…”

“…4) It can be argued that low energy ion bombardment can induce defects which may diffuse into the bulk and form electrically active complexes. However, it has been shown that it only produces one defect, E 0.31 [16] and this defect does not diffuse into the material. The defect introduced during ICP is a subthreshold defect, created when a pre-existing defect site is modified, that only diffuses into Ge at a temperature or length of time far exceeding that experienced during ICP.…”

“…However, using Auger electron spectroscopy it was not possible to find any trace of Ar after ICP and it has been shown that similar long range energy transmission occurs with electron beam deposition and exposure where Ar is not involved [22]. Also, the effect was independent of crystal orientation [16] while channelling should depend on it.…”

Rare Earth Interstitials in Ge: A Hybrid Density Functional Theory Study

“…Impurities influence Ge-based semiconductor devices either positively or negatively [6]. Several experimental and theoretical studies of point defects such as vacancy [13] and interstitial [6,7] defects in Ge have been reported in the literature. While RE ion defects in Si and other materials have been studied both theoretically and experimentally [14][15][16], except for Tm [2,8], the structural and electronic properties of RE interstitial defects in Ge have not been experimentally or theoretically reported.…”