Fermi-level pinning and Schottky barrier heights on epitaxially grown fully strained and partially relaxed n-type Si1−xGex layers

Abstract

The Schottky barrier height on n-type Si1−xGex films has been studied as a function of the composition and strain relaxation. We have used electrical I–V measurements complemented by high-resolution x-ray measurements for assessment of the relaxation in the epilayers. In addition, Schottky barrier height on n-Si1−xGex films has also been investigated as a function of the metal work function. Our results shows that the barrier height on n-type Si1−xGex does not depend on either the Ge content or strain relaxation, but is sensitive to the metal work function. The experimental results indicate that the Fermi level is pinned to the conduction band and provide also the evidence that the pinning position of the Fermi level is metal work function dependent. This pinning behavior in metal Si1−xGex is opposed to that observed in metal/Si contacts, were the Fermi level is pinned either to the valence or conduction band depending on the metal work function. These findings regarding the relaxation independent barrier height on n-type Si1−xGex are suggesting only the movement of the valence band of Si1−xGex/Si heterostructure upon relaxation as expected.

Deep-level transient spectroscopy study of theEcenter inn−Siand partially relaxedn−Mamor1, Elzain2, Bouziane3 et al. 2008Phys. Rev. BSelf Cite7350View full textAdd to dashboardCite

“…From HRXRD measurements, it was confirmed that there was a lattice relaxation in the n-Si 0.9 Ge 0.1 epilayers and the average relaxation factor was determined to be Ϸ 22%. 15 The thickness of the Si 0.9 Ge 0.1 epilayer was 480 nm which is well above the experimentally 16 and theoretically 17,18 calculated critical layer thickness. The Ge content ͑x = 0.04 and 0.10͒ was determined by Rutherford backscattering spectrometry and was found to be uniform within the SiGe epilayers.…”

Fermi level position at metal Si1−x−yGexCy interfaces

“…For example, in the case of Pd/p-Si 1Ϫx Ge x ͑with 0.14рxр0.25͒, contradictory results have been reported: either large SBH values (⌽ Bp у0.70 eV) 13 or small values (⌽ Bp р0.30 eV͒ 16 have been published. Similarly, for as-deposited Pt or Pd on n-SiGe contacts, both a decrease of ⌽ Bn with x 17 and a constant behavior of ⌽ Bn with x 16,19 have been observed. It is worth noting that few groups 16,19,22,25 have studied contacts on both n and p types.…”

“…Similarly, for as-deposited Pt or Pd on n-SiGe contacts, both a decrease of ⌽ Bn with x 17 and a constant behavior of ⌽ Bn with x 16,19 have been observed. It is worth noting that few groups 16,19,22,25 have studied contacts on both n and p types. In some of these last investigations, it is reported that for a given metal and increasing x ͑Fe, 16 Pt, 16 Pd, 19 W, 22 Zr, 25 ͒, the SBHs on n-type Si 1Ϫx Ge x remain almost constant while those on p type follow the trend expected for the band gap.…”

“…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.…”

Schottky Barrier Height Engineering on NiSiGe/SiGe Contacts

“…In one particular study, Schottky barrier heights of the metals tested congregate at 0.60-0.65 eV below conduction band on nSiGe-substrate with increasing Ge concentrate [6]. Although almost all studies indicate decreasing Schottky barrier height on p-SiGe with increasing Ge concentration, studies were inconsistent with regards to Schottky barrier height on n-SiGe with increasing Ge concentration [7][8][9]. Nevertheless, regardless of whether or not Schottky barrier height is solely dependent on the metal work function as in the case of pure Si substrate, it would be good to see if the effective barrier height can be varied by controlling the concentration of depants on the SiGe surface.…”