Electrical properties and degradation kinetics of compensated hydrogenated microcrystalline silicon deposited by very high-frequency-glow discharge

Microcrystalline silicon (µc-Si:H) layers deposited by the very high-frequency-glow discharge technique at a radio-frequency excitation of 70 MHz are observed to be basically slightly <i>n</i> type. By doping (so-called ``microdoping'') with boron in the gas phase volume part per million (vppm) range, compensated material could be obtained. The influence of this doping on the electronic transport properties is documented. A pronounced onset of the boron incorporation into the films measured by secondary-ion-mass spectrometry is observed around 3 vppm (B<sub>2</sub>H<sub>6</sub>/SiH<sub>4</sub>), together with marked changes in the electrical properties. The compensated film obtained for a microdoping of about 1 vppm shows the lowest dark conductivity [3×10<sup>−8</sup> (Ω cm)<sup>−1</sup>], the highest activation energy (517 meV), and, finally, the highest photoconductive gain of 6×10<sup>3</sup> (photo/dark current ratio). Depending on the value of the activation energy (the critical value is  0.2 eV), two different transport models are identified, corresponding to ``Meyer–Neldel'' or ``anti-Meyer–Neldel'' behavior. As for light-induced degradation, the compensated film exhibits better stability than undoped films. Finally, the use of slightly boron doped µc-Si:H as photovoltaically active material will be discussed.