Electron spin resonance in thin film silicon after low temperature electron irradiation O. Astakhov a,b, ⁎ , F. Finger a , R. Carius a , A. Lambertz a , Yu. Petrusenko b , V. Borysenko b , D. Barankov b a Forschungszentrum Jülich, Institute of Photovoltaics, 52425 Jülich, Germany b National Science Center-Kharkov Institute of Physics & Technology, Institute of Materials Science & Technology, 61108, Kharkov, Ukraine Available online 16 January 2007 Abstract Paramagnetic defects in amorphous and microcrystalline silicon (a-Si:H and μc-Si:H) with various structure compositions and doping levels were investigated by electron spin resonance (ESR). Samples were prepared by PECVD. The defect density was varied with 2 MeV electron bombardment at 100 K and stepwise annealing in the range of 80 K–433 K. In intrinsic material the spin density of the dominant ESR signal, presumably originating from dangling bonds (db), increases by up to 3 orders of magnitude after irradiation. In doped μc-Si:H material the pronounced conduction electron (CE) resonance disappears after irradiation and is replaced by the db resonance like in the irradiated intrinsic material. Generally the initial spin density and the line shape can be restored upon annealing at 433 K. Additional features at g-values of g ≈ 2.010 and g ≈ 2.000 in the ESR spectra are observed after irradiation together with the strongly enhanced Si db line at about g = 2.004–2.005. These features decrease rapidly on the first annealing steps and cannot be observed after the final annealing stage. © 2006 Elsevier B.V. All rights reserved. Keywords: Amorphous and microcrystalline silicon; Electron irradiation; ESR; Defects 1. Introduction Structural defects which result in deep-gap or tail states in disordered silicon films like amorphous (a-Si:H) and micro- crystalline (μc-Si:H) silicon are of greatest importance for the electronic quality of these materials. The influence of these states on transport and recombination determine the perfor- mance in thin film devices such as solar cells. However, in- vestigation and understanding of such defects, in particular in the mixed phase material μc-Si:H, is still a challenge. A suc- cessful method to study defects in a-Si:H and μc-Si:H is electron spin resonance (ESR). It was shown that both in a-Si:H and in μc-Si:H the paramagnetic defects, which are detected by ESR, represent the majority of deep defects in the material [1,2]. In addition it is possible to investigate paramagnetic tail states when by doping the Fermi level is shifted closer to the mobility or band edge. To investigate the effect of defects on the electronic properties it is desirable to vary the defect density in one and the same sample. Similarly it is desirable to probe a wide range of gap energies. Both requests are successfully approached by variation of the defect density by electron irradiation and stepwise annealing [3–8]. In intrinsic material this will vary the density of dominating dangling bond type defect [3–7]. In doped material variation of the db density will lead to a Fermi level shift first deep into the gap (after irradiation) and then back into the tail states towards the mobility edges (after annealing) [9]. In general such defect creation is reversible by annealing close to the material preparation temperature [4–8]. Recently we have established a sophisticated irradiation and annealing experiment, which allows a sample treatment cycle from irradiation to ESR measurement where the sample is kept at 100 K [8]. This guarantees creation and preservation of a high defect density, which would otherwise be already partly annealed by sample treatment and storage at room temperature. Based on these earlier experiments we continue our study on high quality μc-Si:H and a-Si:H material. A strong interest is for a mixed phase material with up to 50% amorphous structure, Thin Solid Films 515 (2007) 7513 – 7516 www.elsevier.com/locate/tsf ⁎ Corresponding author. Forschungszentrum Jülich, Institute of Photovoltaics, 52425 Jülich, Germany. Tel.: +49 2461 61 39 23; fax: +49 2461 61 37 35. E-mail address: o.astakhov@fz-juelich.de (O. Astakhov). 0040-6090/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2006.11.115