Defects in the band gap of CuIn1−xGaxSe2 have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga)=0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content.

Articles you may be interested inNa incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structureThe chemical composition of the ͑112͒B surface of epitaxial CuInSe 2 thin films is investigated by angle resolved x-ray photoelectron spectroscopy. Results show that a severe Cu depletion exists in the top 1-2 atomic layers. No bulk second phase is found at the surface. The source of this depletion and its relation to the Cd doping at the CdS/CuInSe 2 interface are discussed.

The chemical composition of the CuInSe2/CdS heterojunction interface is investigated by angle resolved x-ray photoelectron spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy in combination with selective etching of CdS. We demonstrate that ∼0.8 monolayer of Cd is incorporated into the first 1–3 atomic layers of the CuInSe2. This is accompanied by significant Cu depletion with respect to In in the same region. The results suggest that CdCu defects heavily dope CuInSe2 surface n type and cause the observed large band bending on the CuInSe2 side of the heterojunction.

Epitaxial Cu(In, Ga)Se 2 ͑CIGS͒ films were grown on ͑110͒-oriented GaAs substrates using a hybrid sputtering and evaporation process. The morphological and structural properties were determined by scanning electron microscopy, atomic force microscopy, x-ray diffraction, and electron backscatter diffraction. Pronounced faceting was observed on the surfaces of the films and Ga diffusion was observed at higher growth temperatures from the substrates into the films. The ͑220͒/͑204͒ surface of CIGS was found to be unstable under the growth conditions. The resulting surface consists entirely of ͕112͖ type facets with no observable ͑220͒/͑204͒-oriented surfaces. The epitaxial temperature for the ͑220͒/͑204͒ layers is considerably lower than that on any other surface tested and is attributed to the reduced diffusion distance required for adatoms to reach growth sites. The surface is proposed to grow by rapid nucleation and gradual growth of Se terminated steps across Se terminated surface terraces. This causes the Se-terminated terraces to be rough and leaves the metal-terminated terraces, on which nucleation is slow, relatively smooth.

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