Ac Surface Photovoltage Research Articles

An Investigation of the Energy Levels within a Common Perovskite Solar Cell Device and a Comparison of DC/AC Surface Photovoltage Spectroscopy Kelvin Probe Measurements of Different MAPBI3 Perovskite Solar Cell Device Structures

ABSTRACTWe present a study of the energy levels in a FTO/TiO2/CH3NH3PbI3/Spiro solar cell device. The measurements are performed using a novel ambient pressure photoemission (APS) technique alongside Contact Potential Difference data from a Kelvin Probe. The Perovskite Solar Cell energy band diagram is demonstrated for the device in dark conditions and under illumination from a 150W Quartz Tungsten Halogen lamp. This approach provides useful information on the interaction between the different materials in this solar cell device. Additionally, non-destructive macroscopic DC and AC Surface Photovoltage Spectroscopy (SPS) studies are demonstrated of different MAPBI3 device structures to give an indication of overall device performance. AC-SPS measurements, previously used on traditional semiconductors to study the mobility, are used in this case to characterise the ability of a perovskite solar cell device to respond rapidly to chopped light. Two different device structures studied showed very different characteristics: Sample A (without TiO2): (ITO/PEDOT:PSS/polyTPD/CH3NH3PbI3/PCBM) had ∼4 times the magnitude of AC-SPS response compared to Sample B (including TiO2): (ITO/TiO2/ CH3NH3PbI3/Spiro). This demonstrates that the carrier speed characteristics of device architecture A is superior to device architecture B. The TiO2 layer has been associated with carrier trapping which is illustrated in this example. However, the DC-SPV performance of sample B is ∼5 times greater than that of sample A. The band gap of the MAPBI3 layer was determined through DC-SPS (1.57 ± 0.07 eV), Voc of the devices measured and qualitative observations made of interface trapping by DC light pulsing. The combination of these (APS, KP, AC/DC-SPV/SPS) techniques offers a more general method for measuring the energy level alignments and performance of Organic and Hybrid Solar Cell Devices.

Translation from Schottky Barrier to Atomic Bridging-Type Surface Photovoltages in Cr-Aqueous-Solution-Rinsed Si(001) Wafers

The Cr(OH)3/n-Si Schottky-barrier-type AC surface photovoltage (SPV) in n-type Si(001) wafers fades away during long air exposure at room temperature and/or thermal oxidation at 100 °C for a short time (10 min), indicating a collapse of the Schottky barrier. At 100 °C, the AC SPV reappears with a longer duration time in n-type Si wafers, explaining the occurrence and growth of a negative oxide charge because of the formation of an atomic bridging (CrOSi)- or CrO2- network reported previously. At 200 °C, the AC SPV approaches a strong inversion state in n-type Si. In contrast, in p-type Si(001) wafers, the AC SPV decreases with oxidation duration time at 100 °C. At 200 °C, the AC SPV completely disappears in p-type Si. This result explains why a positive fixed oxide charge in p-type Si was compensated for by the growth of a Cr-induced negative charge [(CrOSi)- or CrO2- network]. This reverse interrelation gives evidence that the translation occurs from the Schottky barrier to the atomic bridging AC SPV, and thus the Cr-induced negative charge can be proved to be described as (CrOSi)- and/or CrO2- networks as well as (AlOSi)- or (FeOSi)- networks that were demonstrated previously.

Collapse of Cr(OH)3/n‐Si Schottky barrier and growth of atomic bridging–type surface photovoltages in Cr‐deposited n‐type Si(001) wafers

In Cr aqueous solution–rinsed n‐type Si(001) wafers, long air exposure at room temperature and/or thermal oxidation for a short time (10 min) at 100 °C collapses the Cr(OH)3/n‐Si Schottky barrier, transforming into the atomic bridging–type (Cr‐induced negative charge) surface photovoltage (SPV). For further duration time of oxidation at 100 °C, frequency‐dependent AC SPV reappears, indicating the occurrence and growth of a negative charge in SiO2 thin films possibly because of the formation of a (CrOSi)− or CrO2− network. At 200 °C for 10 min, the AC SPV frequency becomes proportional to 1/f (f, frequency), resulting in a strongly inverted state. This result provides evidence that the translation from the Schottky barrier to the atomic bridging–type AC SPV occurs and thus the Cr‐induced negative charge can be described as (CrOSi)− and/or CrO2− networks as well as (AlOSi)− or (FeOSi)− demonstrated previously. Copyright © 2012 John Wiley & Sons, Ltd.

Schottky-Barrier-Induced AC Surface Photovoltages in Au-Precipitated n-Type Si(001) Surfaces

We have studied the behavior of Au clusters on the top surface of a SiO2 film and/or at the SiO2/Si interface as a function of oxidation temperature between room temperature (RT) and 500 °C in conjunction with a Schottky-barrier-induced AC surface photovoltage (SPV) and an enhanced SiO2 growth due to Au at 500 °C. Upon rinsing an n-type Si(001) wafer in a Au-contaminated aqueous solution, precipitated Au atoms are observed as clusterlike Au granules on the top surface of SiO2 (Au surface concentration, 2.3 ×1015 atoms/cm2). In thermally oxidized Au-contaminated n-type Si(001) wafers between 100 and 500 °C, a Au cluster of a similar shape is also observed. Chemical analysis gives evidence that Au existed at the SiO2/Si interface, which produced Au/n-Si Schottky-barrier-type AC SPV between 100 and 500 °C as well as at both RT and higher temperatures, indicating that the Au/n-Si Schottky barrier remains in a similar manner. In the Au-contaminated n-Si thermally oxidized at 500 °C, the catalytic action of Au atoms enhances SiO2 growth as well as the case at high temperatures between 750 and 900 °C. The mechanism of the enhanced growth is proposed.

Schottky-Barrier-Induced AC Surface Photovoltages in Au-Precipitated n-Type Si(001) Surfaces

Schottky-Barrier-Induced AC Surface Photovoltages in Au-Precipitated n-Type Si(001) Surfaces

周波数依存交流表面光電圧法に基づく熱酸化したSi(100)ウェーハにおけるFe誘起負電荷の検証

周波数依存交流表面光電圧法に基づく熱酸化したSi(100)ウェーハにおけるFe誘起負電荷の検証

交流表面光電圧法によるSi(100)表面におけるCrショットキー障壁からCr誘起負電荷への変化の検討

交流表面光電圧法によるSi(100)表面におけるCrショットキー障壁からCr誘起負電荷への変化の検討

Novel noncontact approach to monitoring the field-effect passivation of emitters

Abstract We report a comprehensive noncontact approach to measurement of the field-effect passivation of emitters for p and n-type base silicon solar cells. The corona charge-voltage technique, extensively used in silicon IC fabrication lines, is utilized in an automated sequence with two complementary measurements that monitor charge induced changes of recombination in the emitter. Quasi-steady-state microwave photoconductance decay, QSS-μPCD measures decay lifetime τeff, the injection level, Δn and the emitter saturation current, J0. UV and blue ac-surface photovoltage (UV-SPV) gives a passivation indicator analogous to short wavelength quantum efficiency. Field-effect characteristics of τeff, Seff, J0, and UV-SPV are presented for symmetrical n + and p + emitter test wafers that quantify the effect of charge, polarity and differences between n + and p + emitters. New findings include field effect hysteresis and charging induced emitter degradation phenomenon analogous to stress induced degradation in MOS devices.

Novel Noncontact Approach to Characterization of Mobility in Inversion Layers Using Corona Charging of Dielectric and SPV Monitoring of Sheet Resistance

A recently proposed noncontact method for mobility measurement in an inversion layer created by corona charging is modified taking advantage of two unique features of corona-voltage metrology; 1. the exact knowledge of the corona charge placed on dielectric surface and 2. the straightforward determination of the semiconductor space charge potential barrier, Vsb. These features, not available in MOS measurements simplify determining the inversion charge, Qinv. Combined with ac-surface photovoltage measurement of the inversion layer sheet resistance, Rs, they are a basis for novel simplified approach to mobility measurement. The method is illustrated using SiO2 and high-k stacked dielectrics on p-Si.

Negative Oxide Charge in Thermally Oxidized Cr-Contaminated n-Type Silicon Wafers

The evaluation of thermally oxidized Cr-contaminated Si surfaces, by an AC surface photovoltage (SPV) method, indicates that a certain amount of contaminating Cr atoms resides in the SiO2 thin film, resulting in the creation of a negative oxide charge in the form of a (CrOSi)- and/or CrO2- networks, which are postulated to be analogous to the (AlOSi)- network. For samples oxidized at temperatures between 550 and 700 °C for 10 min, the AC SPV gives evidence that the induced negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 700 °C and/or a longer oxidation time than 10 min, AC SPV is reduced, meaning that the strongly inverted state changes into a less depleted state, and finally, the AC SPV disappears. In this case, a collapse of the (CrOSi)- and/or CrO2- networks is expected with a possible change into Cr2O3.

Semiconductor Thin Film Characterization with ac Surface Photo Voltage

Surface Photo Voltage (SPV) method is proven to be well-suited for accurate and non-destructive characterization of semiconductor thin films due to its high sensitivity to the near surface region. Presented data and analysis encompasses wide range of ac-SPV technique capabilities. A physical model describing measurement regimes is discussed. The results agree with the theory and correlate with the data obtained with alternative measurement techniques.

Semiconductor Thin Film Characterization with AC Surface Photovoltage

not Available.

Quantitative Estimation of Aluminum-Induced Negative Charge Region Top Area of SiO2 Based on Frequency-Dependent AC Surface Photovoltage

Most aluminum (Al) in Al-contaminated and thermally oxidized n-type silicon (Si) dioxide (SiO2) is clarified to be segregated at the very top area of SiO2, causing a negative charge, as has been suggested by the formation of an (AlOSi)- network and/or AlO2- based on AC surface photovoltage (SPV). For a strongly inverted state at an oxidation temperature of 800 °C for 1 h, the thickness of the Al-induced negative charge region is quantitatively determined to be 2.4 nm on the basis of AC SPV after successive step etching and chemical analysis. As oxidation duration increased at 800 °C for 3 h, the strongly inverted state changed into a weakly inverted state, where the thickness of the Al-rich region is reduced (0.8 nm), proving that more than half of the (AlOSi)- network collapse and/or Al diffuses inside SiO2 during a longer oxidation duration.

Size- and Orientation-Dependent Photovoltaic Properties of ZnO Nanorods

ZnO nanorod arrays on an ITO substrate and nanorod powder have been prepared via a chemical method in aqueous solution at low temperature. Two dimensions of composite nanorods in the arrays were obtained by controlling the reaction time. SEM, XRD, UV−vis transmission, and PL measurements have been utilized to characterize the samples. The surface photovoltage (SPV) spectra of the three samples have been comparatively investigated by a lock-in amplifier with dc bias and Kelvin probe (KP) based measurements. The kinetic features of SPV responses are interpreted in terms of ac SPV phase spectra and SPV transients on a KP. We demonstrate that the photovoltaic properties of ZnO nanorods not only depend on the rod size, but also rely on the crystallographic orientation. The mechanisms therein have been discussed in detail. Our results could lead to better understanding of the photovoltaic properties in ZnO nanostructures.

Manifestation of Cu Impurities on Silicon Surfaces, Implication for Monitoring Cu Contamination

The electrical manifestations of Cu on silicon surfaces were investigated using Contact Potential Difference (CPD) and ac-Surface Photovoltage (SPV) measurements of Si intentionally contaminated with Cu. The corresponding physical model involves Cu-induced surface states. The Cu-induced negative surface charge is manifested by an increase of the work function and a decrease of the surface depletion barrier,Vsb, in p-type Si and an increase in n-type Si. The SPV manifestation of Cu is a decrease of the surface lifetime, tau s. These manifestations should enable Cu monitoring within the 1e8 atom/cm2 range. In practice, this limit is not reached because only a small fraction of surface Cu is electrically active. This obstacle is overcome using an optical surface treatment that electrically activates surface Cu and isolates the Cu contribution. With this approach we demonstrated Cu detection in the 1e9 atoms/cm2 range using Vsb and in the 1e10 atoms/cm2 range using tau s.

Analysis of Au/Si Schottky barrier type AC surface photovoltage in silicon wafer surface dipped into Au aqueous solution

AbstractThe state of a gold (Au)‐contaminated silicon (Si) surface dipped in an aqueous solution, with a standard Au solution, was investigated using the alternating current surface photovoltage (AC SPV) method [1, 2]. On a Au‐contaminated n‐type Si wafer surface, frequency‐dependent AC SPV was observed and it was shown that the n‐type Si surface was in a depleted or weakly inverted state. The cutoff frequency was found from the AC SPV frequency dependence curve of the Au‐contaminated n‐type Si wafer and an analysis of the Si surface potential was performed. With those results, the band diagram of the Au/n‐type Si Schottky contact was found and a Schottky barrier height ΦB was calculated as 0.73 to 0.76 eV. This value is close to the reported value ΦB=0.79 eV and supports the formation of a Au/n‐type Si Schottky barrier. From these results, a model for AC SPV occurrence is proposed in which the n‐type Si surface is weakly inverted with the formation of a Au/n‐type Si Schottky barrier. Meanwhile, in a Au‐contaminated p‐type Si wafer, the measured voltage was the noise level of the measurement device and indicates a low surface potential. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(6): 27–33, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20308

Anomalous Behavior of Schottky Barrier-Type Surface Photovoltages in Chromium-Contaminated N-Type Silicon Wafers Exposed to Air

A study of frequency dependent AC surface photovoltages (SPV) in n-type silicon (Si) wafers contaminated with an aqueous solution containing chromium (Cr) was carried out. Immediately after rinsing (5 min exposure to air), the Cr (Cr3++3e- →Cr) deposited on the surfaces of the wafers had already been converted into Cr(OH)3 and/or Cr2O3. This Cr(OH)3–Si contact forms a Schottky barrier on n-type Si. This gives rise to depletion and/or an inversion layer formed at the surface, resulting in the appearance of a frequency-dependent AC SPV. With exposure to air, the AC SPV in n-type Si wafers was reduced. This happens because Cr is oxidized and the Cr(OH)3 becomes Cr2O3 through the reaction 2Cr(OH)3 →Cr2O3+3H2O, thus reducing the Schottky barrier height. Another factor is compensation by the positive oxide charge formed when the surface goes into accumulation, resulting in a suppression of the AC SPV in n-type Si. A schematic band diagram of the Schottky barrier was developed, and the barrier height was calculated to be 0.75 eV for n-type Si.

Quantitative Estimation of the Metal-Induced Negative Oxide Charge Density in n-Type Silicon Wafers from Measurements of Frequency-Dependent AC Surface Photovoltage

A quantitative estimation of metal-induced oxide charge (Qmi) density is performed on the surface of n-type silicon (Si) wafers rinsed with trivalent aluminum (Al)- and iron (Fe)-contaminated RCA alkaline solution by analyzing the frequency-dependent AC surface photovoltage (SPV). Qmi arises from (AlOSi)- or (FeOSi)- networks in native oxide which are responsible for inducing negative oxide charge. On the basis of Munakata and Nishimatsu's half-sided junction model [C. Munakata and S. Nishimatsu: Jpn. J. Appl. Phys. 25 (1986) 807], the network densities are estimated in depletion and/or weak inversion in which the cutoff frequencies of the frequency-dependent AC SPV curves are defined. It is found that the charge density Qmi increases with the time of exposure to air and it is calculated that about 4% of Al atoms in the native oxide are activated in the form of an (AlOSi)- network for 1 h of exposure. The (FeOSi)- network density is calculated as a function of Fe concentration. As a result, the frequency-dependent AC SPV measurements carried out here enable a successful evaluation of impurity level in a nondestructive and noncontact manner.

Behavior of Metal-Induced Negative Oxide Charges on the Surface of N-type Silicon Wafers Using Frequency-Dependent AC Surface Photovoltage Measurements

The metal-induced negative charge on the surface of n-type silicon (Si) wafers, previously reported in the atomic bridging model as (AlOSi)- and (FeOSi)- networks, was investigated using AC surface photovoltage (SPV) as a function of the frequency ( f) of a chopped photon beam, with the aid of an AC SPV instrument developed in-house. A frequency-dependent AC SPV in Al-contaminated wafers was observed immediately after the rinsing. In the early stages of exposure to air at room temperature after rinsing, the induced AC SPV at frequencies of less than approximately 100 Hz was flat with frequency. This indicated that majority carrier conduction was the dominant mechanism, suggesting that the surface was depleted and/or weakly inverted. With the passage of time, the AC SPV in the lower frequency region increased, yielding an AC SPV vs frequency relationship approaching 1/ f. This demonstrated that the Al-induced negative charge [(AlOSi)-] increased and finally became limited by the depletion layer capacitance (strongly inverted state). The frequency-dependent AC SPV caused by Fe-induced negative charge [(FeOSi)-] was identified as being dependent on Fe concentration on the Si surface. The higher the Fe concentration, the more strongly inverted the Si surface became. The metal-induced oxide charge could be observed, together with other oxide charges such as fixed oxide charge.

Atomic Bridging and Barrier-Type AC Surface Photovoltage Measurements on Iron- and Copper-Contaminated Silicon Surfaces

The rise time of the alternating current (ac) surface photovoltage (SPV) of n-type silicon (Si) contaminated by Fe and/or Cu aqueous solutions was investigated. After a rinse time of about 1000 min in Fe contaminated water, three monolayers (0.59 nm) of oxide were formed, with a resulting incorporation of Fe. The variation of ac SPV signals indicated the appearance of a negative charge corresponding to the increasing concentration of Fe on surface of the Si wafer. This negative charge can be accounted for by postulating a bridging mechanism between trivalent Fe ions, and quadrivalent Si ions, forming an network in the native oxide. In contrast to Fe, Cu was deposited at the beginning of the rinsing on partially hydrophobic n-type Si surfaces as an Cu atomic layer or Cu particles (maximum Cu concentration: around resulting in a Cu-Si contact. Because the reduction potential of is larger than that of Si, the process was accomplished through electron capture. It is postulated that the Cu-Si contact may have formed a Schottky barrier between the Cu and n-type Si, resulting in the occurrence a so-called barrier-type ac SPV. This may prove to be a promising method for fabricating atomic layer Schottky devices. © 2003 The Electrochemical Society. All rights reserved.