Abstract
Workfunction of reactive-plasma deposited indium-tin-oxide (RPD-ITO) at the ITO/SiO2 interface, which is referred as interface workfunction, and the process-induced damage are experimentally extracted for the first time based on capacitance-voltage (C-V) analysis. The estimated interface workfunction value of 4.74 eV for as-deposition condition is about 0.4 eV higher than that in the bulk determined by ultraviolet photoelectron spectroscopy (UPS). The RPD process induces the damage at the Si/SiO2 interface, and the degree of the damage is evaluated as the interface defect density (Dit) to be around 1012 cm-2eV-1. The effects of forming-gas annealing on the interface workfunction and recovery of the damage are also studied. The interface workfunction value once decreases to 4.53 eV by the annealing up to 250 oC and then turns to increase to 4.77 eV after 400 oC annealing. The damage is annihilated by the low-temperature forming-gas annealing at 200 oC.
Highlights
Workfunction of a transparent conductive oxide (TCO) at a TCO/insulator interface, which is referred as “interface workfunction” in this paper, is an important factor to determine the electrical properties of TCO/insulator/semiconductor stack devices such as solar cells with carrier-selective contacts (CSCs)[1] and other optoelectronic devices
In several earlier works reporting on the workfunction of TCOs such as indium-tin oxide (ITO)[2,3,4] and molybdenum oxide (MoOx)[5,6] etc, the values were obtained as the bulk materials determined by ultraviolet and/or x-ray photoelectron spectroscopy (UPS/XPS)
The variation in the C-V curves is shown in Fig. 7, which was obtained before and after the forming-gas annealing (FGA) at temperatures of 200, 250, 300 and 400 oC for the ITO/SiO2/Si stack with the SiO2 thickness of 30.5 nm
Summary
Workfunction of a transparent conductive oxide (TCO) at a TCO/insulator interface, which is referred as “interface workfunction” in this paper, is an important factor to determine the electrical properties of TCO/insulator/semiconductor stack devices such as solar cells with carrier-selective contacts (CSCs)[1] and other optoelectronic devices. The process-induced damage has been characterized by lifetime spectroscopy.[14] the measured lifetime reflects the effect of defects at the interface and charged states in the insulator and that of the workfunction difference between TCO and Si. it is required to extract separately the above-mentioned interface workfunction and processinduced damage for TCO/insulator/Si stacks. Workfunction of a TCO at the TCO/insulator interface and the process-induced damage during the TCO deposition are extracted by C-V analysis. ITO is chosen as one of the typical TCOs since this material is a well-known material and often used in the various kinds of photoelectron devices.[19,20] The obtained values of interface workfunction are compared with those of bulk workfunction determined by UPS for the same device. The effects of the post-deposition annealing, which is performed to annihilate the damage, on the variation in the interface workfunction and Dit are discussed
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