Electrical and Structural Characterization of Ti Contacts to Si_0.89 Ge_0.11/Si(001) Epilayers

Abstract

The properties of thin (350 Å) Ti layers deposited on Si0.89Ge0.11 layers epitaxially grown on Si(001) were studied as a function of isochronal (30 min.) thermal treatments in the temperature range Ta=550–800°C. Both as-deposited and annealed at Ta up to 750°C Schottky diodes revealed near-ideal I–V and C–V characteristics with the same flat-band barrier height eV. The results indicate that at these Ta the Fermi level is pinned with respect to the conduction band.Annealing at 800°C resulted in an improvement of the Schottky diodes quality and a drop in and the series resistance Rs of the contacts. The values of the ideality factor n and ( measured were 1.03±0.02 and 0.56±0.007 eV, correspondingly. The electrical parameters of these metal/semiconductor contacts were correlated with the dynamics of interfacial reactions due to the applied heat-treatments.

Electrical properties of the Ti(SiGe)2/Si0.89Ge0.11/Si(001) contact system

“…The thickness of the residual Si 1Ϫx Ge x (xϷ0.11) epitaxial layer is somewhat smaller than after the 750°C anneal. X-ray analysis, as mentioned earlier, 15 reveals in this case the presence of only two phases: the residual Si 0.89 Ge 0.11 layer with a strain degree Ϸ63% and the C54-Ti͑Si 0.91 Ge 0.09 ͒ 2 phase. It means that the 800°C anneal produces a uniform mechanical mixture of these phases adjacent to the surface of the sample.…”

“…12,13 The applicability of Ti as a contact material for Si makes it also a potential candidate as a contact material to SiGe. In a previous work, 15 we have reported on the electrical properties of the Ti/n-SiGe/Si(001) interface as a function of applied heat treatments, and correlated them with structural and compositional changes of the interfacial region. It was shown that isochronal ͑30 min͒ annealings at T a Ͻ800°C resulted in nearly ideal Schottky barrier characteristics.…”

Fermi level position at metal Si1−x−yGexCy interfaces

“…We can also find studies devoted only to n-type contacts. 17,18,27 Two types of behavior have been observed on n-type layers. Either ⌽ Bn is constant with x within 30 meV or less ͓Nur ͑Pt, Fe͒, 16 Shinoda ͑Zr͒, 25 Meyer ͑W͒, 22 Mamor ͑Pd͒ 19 and Lyakas ͑Ti͒ 27 ͔, or ⌽ Bn varies with x. Liou ͑Pt, Pd͒ 17 and Buxbaum (Pd 2 Si) 18 reported a decrease of ⌽ Bn with x, while Shinoda observed an increase of ⌽ Bn (x) for Ti.…”

“…4,6,11 On the other hand, the rather recent interest in Si 1Ϫx Ge x alloys has generated few studies on Schottky contacts and the results are still puzzling. In the literature, we have pointed out results obtained with metals such as Al, 12,13 Pd, [13][14][15][16][17][18][19] Pt, [14][15][16][17]20 Ir, 16,20 W, [21][22][23][24] Zr, 25,26 Ti, [24][25][26][27] Fe 16 and Sc. 28 In all the studies on p type, a common trend of the SBH (⌽ Bp ) has been observed: ⌽ Bp decreases with increasing the Ge content ͑x͒ in the Si 1Ϫx Ge x epilayer.…”

“…28,30,31 In addition, the SBH can be disturbed by any thermal treatment, and some of the results previously quoted have been measured after a thermal reaction between the metal and the semiconductor. [12][13][14][15]18,27 In some cases, a Si-cap layer has even been incorporated between the metal and the semiconductor. 12,13,20 In the case of SiGeC alloys, the SBHs have been even less investigated.…”