Electrical Properties and Degradation Kinetics of Compensated Hydrogenated Microcrystalline Silicon Deposited by the 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 〈n〉 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 (B2H6/SiH 4), together with marked changes in the electrical properties. The compensated film obtained for a microdoping of about 1 vppm shows the lowest dark conductivity [3×10-8 (Ω cm)-1], the highest activation energy (517 meV), and, finally, the highest photoconductive gain of 6×103 (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. © 1995 American Institute of Physics.