The constant photocurrent method in the ac-mode （ac-CPM） is used to determine the defect density of states （DOS） in hydrogenated microcrystalline silicon （μc-Si：H） prepared by very high frequency plasma-enhanc...The constant photocurrent method in the ac-mode （ac-CPM） is used to determine the defect density of states （DOS） in hydrogenated microcrystalline silicon （μc-Si：H） prepared by very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD）. The absorption coefficient spectrum （ac-α （h v））, is measured under ac- CPM conditions at 60 Hz. The measured ac-α（hv） is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band- tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α（hv） in the present work and a previously measured transient photocurrent （TPC） for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α（h v） is found to agree satisfactorily with the measured ac-α （h v）.展开更多
文摘The constant photocurrent method in the ac-mode （ac-CPM） is used to determine the defect density of states （DOS） in hydrogenated microcrystalline silicon （μc-Si：H） prepared by very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD）. The absorption coefficient spectrum （ac-α （h v））, is measured under ac- CPM conditions at 60 Hz. The measured ac-α（hv） is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band- tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α（hv） in the present work and a previously measured transient photocurrent （TPC） for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α（h v） is found to agree satisfactorily with the measured ac-α （h v）.
