We investigate the electronic structures of n-type doped CuInS2 crystals wi
th chalcopyrite structures using Zn or Cd species, Cu-substituting species,
as donor dopants based on ab initio electronic band structure calculations
. We find that the strongly localized impurity states for n-type CuInS2 dop
ed with Zn with small decrease in Madelung energy compared with that for n-
type CuInS2 crystals doped with Cd species. This finding indicates that a d
eep donor level below the conduction band will be formed for n-type Zn-dope
d CuInS2 crystals, resulting in high-resistivity n-type CuInS2:Zn. This is
in good agreement with other experiments.
The total energy calculations show that the formation of Cu vacancy in the
vicinity of Zn sites, donor-impurity sites, is energetically favorable for
Zn-doped CuInS,. In other words, the Zn-donor states are compensated by the
Cu-vacancies generated by the Zn doping. On the other hand, for n-type Cd-
doped CuInS2 crystals, we find more distant Cu vacancies from the Cd sites.
From the above findings concerning both the electronic structures and compe
nsation mechanism of Zn-or Cd-doped CuInS, crystals, we predict that Cd spe
cies can be considered as suitable candidates for use as donor dopants, to
fabricate a "buried-homo junction, p-CuInS2/n-CuInS2:Cd/n-CdS" of CuInS2-ba
sed solar cells. (C) 2000 Elsevier Science B.V. All rights reserved. PACS:
73.20.At.