Electronic Properties

The effective mass, is determined by the curvature of the bands at the Г – point, and influences the carrier mobility. Cu(InGa)Se2 films, grown with the excess Se, are p-type with a carrier densities of ~1015-1016 cm-3 (Heath et al. 2004).

CuInSe2 and Cu(InGa)Se2 have the same type of intrinsic defects, such as three vacancies, three interstitials, and six antisites, of which the ones with lowest forma­tion energies are formed. These are, depending on the composition, the Cu vacancy, the In or Ga vacancy, the CuIII or IIICu antisite and the Se vacancy (Wei et al. 1998, 1999).

The Se vacancy are amphoterics defect (Lany and Zunger 2004), which could explain some metastable effects in solar cells. The IIICu antisite defect is related to a DX center (Lany and Zunger 2008), that could limit doping in wide band gap Cu(InGa)Se2.

Photoluminescence and Hall effect on epitaxial film show four dominating shal­low defects, i. e. three acceptors and one donor (Bauknecht et al. 2001; Siebentritt et al. 2004a, 2005). Defect spectroscopy by photoluminescence is more useful in material with Cu-excess (Dirnstorfer et al. 1998; Bauknecht et al. 2001; Shklovskii etal. 1989).

Capacitance measurements identiflcaty two dominant deep defects in all Cu(InGa)Se2 samples: one, sometimes labeled N2, at an energy of 250-300 meV from the valence band (Turcu et al. 2002a), and a deeper one at 800 meV from the valence band (Heath et al. 2002). The N2 defect is far enough away from the mid-gap for all Ga/In ratios and does not act as recombination center. However, the 800 meV defect becomes a mid-gap defect for high Ga contents and may act as recombination center in alloys with larger Ga content.

Updated: August 23, 2015 — 8:15 pm