Features of temperature dependence of contact resistivity in ohmic contacts on lapped n-Si

Abstract

The temperature dependence of contact resistivity q c in lapped silicon specimens with donor concentrations of 5 Â 10 16 , 3 Â 10 17 , and 8 Â 10 17 cm À3 was studied experimentally. We found that, after decreasing part of the q c (T) curve in the low temperature range, an increasing part is registered with increasing temperature T. It is demonstrated that the formation of contact to a lapped Si wafer results in the generation of high dislocation density in the near-surface region of the semiconductor and also in ohmic contact behavior. In this case, current flows through the metal shunts associated with dislocations. The theory developed is in good agreement with experimental results. V C 2012 American Institute of Physics. [http://dx

On a feature of temperature dependence of contact resistivity for ohmic contacts to n-Si with an n + -n doping step

“…Such growing dependences ρ с (Т) were obtained in [5][6][7] for ohmic contacts to lapped as well as polished n-Si, at presence of high density of structural defects in the Si near-contact region. In that case, calculation of the number of defects from etching pits made for lapped silicon gave ~10 7 cm -2 .…”

“…However, recent investigations [2][3][4][5][6][7][8][9] showed that in some cases ρ с does not demonstrate the above behavior. To illustrate, for ohmic contacts to wide-gap semiconductors with high dislocation density it was shown in [2-4, 8, 9] that ρ с increases with temperature.…”

“…It was shown in [10] that the above inequality is valid at doping levels n 2  10 15 cm . It should be noted that the above current mechanism (as well as that related to current flow through the metal shunts associated with dislocationssee [7,8]) ensures purely ohmic contact behavior. At the same time, the standard mechanism that describes slightly non-ohmic contact with low barrier height (about kT/q), as well as the thermofield mechanism of current flow, result in ohmic contact behavior only in the case that R c  R b (here R c is the contact resistance, and R b is the bulk resistance).…”

“…To measure ρ с (Т) over the 125-375 K temperature range, we made test structures with specimens of both types. The configuration of test structures corresponded to ρ с measurement with the transmission line method (TLM) [13] that was used by us earlier in [5][6][7][8]. It enabled us to test ρ с with allowance for either conduction in the n + -layer only (planar configuration of TLM structure) or through the n + -n doping step (vertical configuration of TLM structure).…”

“…In that case, calculation of the number of defects from etching pits made for lapped silicon gave ~10 7 cm -2 . According to the model proposed in [7,8], this value turned out sufficient for description of growing dependence ρ с (Т).…”