Charge Density in Atmospheric Pressure Chemical Vapor Deposition TiO[sub 2] on SiO[sub 2]-Passivated Silicon

Abstract

The charge density of a TiO2 film deposited on a SiO2 -passivated silicon wafer is determined. The TiO2 is deposited by atmospheric pressure chemical vapor deposition at 400°C , and the SiO2 is grown thermally at 950°C . This TiO2–SiO2 stack is a useful coating for the front surface of a silicon solar cell, as it has a high optical transmission and a low density of interface states Dit(E) at the SiO2–Si interface. While these properties are beneficial to high efficiency solar cells, so too is a large charge density, as what occurs in Si3normalN4–SiO2 (+1012cm−2) and Al2normalO3–SiO2 (−1013cm−2) stacks. The Dit(E) and charge density of TiO2 -coated and SiO2 -passivated silicon are evaluated by capacitance–voltage and Kelvin probe measurements. The charge density of the TiO2 is within the conservative limits of −8.5 and −1×1011cm−2 after deposition and of −10 and +1×1011cm−2 after a subsequent 800°C oxygen anneal. Photoconductance measurements suggest that the dangling-bond defects at the SiO2–Si interface are predominantly donorlike and, hence, that the change density in the TiO2 is closer to the upper limits (less negative); this charge is too small to benefit solar cells.

On the c-Si/SiO2 interface recombination parameters from photo-conductance decay measurements

“…The value E 0 takes has been previously suggested to be near the mid-gap. 36,56 Simulations conducted in Section III showed that a value of neutral energy E 0 in the range ÀE g =4 < E 0 < þE g =4 had a negligible effect on SRV, as can also be inferred from Girisch's treatment, 15 and thus, a value E 0 ¼ E g =2 is assumed throughout this work. In general, changes in the dielectric fixed charge can produce changes in both donor and acceptor states at the interface.…”

“…Although D it;q has been typically described by an inverse Gaussian function, additional extensions have been proposed by adding exponential tail functions to model the high density of states near the band edges. 20,56 Despite the high density of such near band tail states, they contribute negligibly to the recombination activity at the surface. This is a consequence of the extended SRH process as described in Section II E. In this work, a three term exponential function is proposed to model D it;q .…”

“…Using the theory set out in Section II, values for D it;q ; S n , and S p were found so that the model best fitted the experiments. The search for parameters started from known previously reported values, 18,20,56 and those calculated from results of C-V measurements. 38,56 The optimal fitting parameters were found by minimising the least-squared weighted errors between modelled and the measured data.…”

Low Voltage Electrowetting-on-Dielectric for Microfluidic Systems

“…The degradation of the material after 325 cycles reported in Figure 50 was evaluated with the SKP, as shown in Figure 53 A charge injection technique is commonly used to determine the integrity of gate oxides in semiconductor fabrication by depositing charge through a corona discharge [165]. If the trapped charge is located within the polymer layer and is significantly larger than the native charge in the aluminum oxide and interface, the charge density is simply given by the potential drop due to the capacitance of the polymer [166], [167]. Under this assumption, the charge derived from the CPD values is estimated to be 5.…”

“…Using the charge density interpretation from the corona charge measurements, the charge density is only given through the potential drop due to the capacitance of the polymer [166], [167]. This suggests that the observed value of charge for zero contact angle change is independent of the underlying oxide layer.…”