Characterization of defect levels in semi-insulating 6H-SiC by means of photoinduced transient spectroscopy and modulated photocurrent technique

Longeaud, Christophe; Kleider, Jean‐Paul; Kaminski, P.; Kozłowski, Roman; Miczuga, M.

doi:10.1088/0953-8984/21/4/045801

Cited by 9 publications

(6 citation statements)

References 20 publications

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“…Qualitatively, the dependence of the first quadrant feature on both device aging duration and excitation intensity is consistent with larger trap densities and occupancies, respectively. − Furthermore, the semicircle arcs comprising the first quadrant contain useful information concerning the relative amounts of trapped charge and otherwise lost to recombination. The so-called generation current represents the device photocurrent output in the absence of charge recombination, which is obtained by taking the real component intercept at the high-frequency limit of the first quadrant region.…”

Section: Resultsmentioning

confidence: 61%

Implications of Trap-Assisted Nongeminate Charge Recombination on Time- and Frequency-Domain Photocurrent Degradation Signatures of Organic Solar Cells

et al. 2020

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Charge transport and collection in organic solar cells are heavily influenced by traps which ultimately limit the ability to harvest all photogenerated carriers. We investigate photocurrent responses of organic solar cells subjected to varying degrees of aging from time-and frequency-domain perspectives. Intensitymodulated photocurrent spectroscopy (IMPS) is primarily used here to resolve the effect of trap-assisted nongeminate charge recombination over a broad frequency range (e.g., ∼1 mHz−1 MHz). We use a combination of IMPS and time-dependent photocurrent transients to understand characteristic degradation signatures (i.e., positive, low-frequency imaginary component and "gain peak" where the real photocurrent exhibits a characteristic maximum, I max , at high frequencies) unique to organic solar cells. As trap densities and occupation increase with aging and light intensity, the photocurrent contrast (i.e., maximum/steady-state photocurrent, I max /I DC ) and the size of the low-frequency imaginary contribution increase. Substantial harmonic content underlies this trend which becomes more prominent as modulation frequencies and trap levels increase. We then use drift-diffusion simulations to describe IMPS responses and photocurrent transient signals over the entire frequency sampling window for aged devices that show excellent agreement with experiment. The results provide deeper insights into trap-related phenomena over a larger frequency bandwidth and further demonstrate the effectiveness of IMPS in its ability to identify mechanistic and kinetic details of degradation.

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Section: Resultsmentioning

confidence: 61%

Implications of Trap-Assisted Nongeminate Charge Recombination on Time- and Frequency-Domain Photocurrent Degradation Signatures of Organic Solar Cells

et al. 2020

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“…11(b) presents the increase in the concentration of holes in the hole trap HT obtained by solving Eq. (7). In this case, the illumination increases the concentration of holes to a value of 6.99 × 10 14 cm −3 , which means that the trap is filled by 99%.…”

Section: Effect Of Defect Centres On the Excess Hole Concentration In...mentioning

confidence: 86%

“…The phenomena associated with the emission and capture of excess electrons and holes by defect centres after switching on the photoexcitation of electron-hole pairs are modelled with the set B Si in both h and k sites [23] of differential-type rate equations The rates of changes in the electron and hole concentrations on the levels of the defect centres are described by equations from ( 2) to (7). The rate of change in the excess electron concentration in the conduction band and the rate of change in the excess hole concentration in the valence band are described by Eqs.…”

Section: Rate Equationsmentioning

confidence: 99%

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Current status of modelling the semi-insulating 4H–SiC transient photoconductivity for application to photoconductive switches

Suproniuk¹,

Kamiński²,

Kozłowski³

et al. 2017

Opto-Electronics Review

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In this paper we present the current status of modelling the time evolution of the transient conductivity of photoexcited semi-insulating (SI) 4H-SiC taking into account the properties of defect centres. A comprehensive model that includes the presence of six, the most significant, point defects occurring in SI 4H-SiC crystals is presented. The defect centres are attributed to the two kinds of nitrogen-related shallow donors, a boron-related shallow acceptor, deep electron and hole traps, and the Z 1/2 recombination centre. We present the results of the state-of-the-art numerical simulations showing how the photoconductivity transients change in time and how these changes are affected by the properties of defect centres. The properties of defect centres assumed for modelling are compared with the results of experimental studies of deep-level defects in high purity (HP) SI 4H-SiC wafers performed by the high-resolution photoinduced transient spectroscopy (HRPITS). The simulated photoconductivity transients are also compared with the experimental photocurrent transients for the HP SI 4H-SiC wafers with different deep-level defects. It is shown that a high-temperature annealing producing the C-rich material enables the fast photocurrent transients to be achieved. The presented analysis can be useful for technology of SI 4H-SiC high-power photoconductive switches with suitable characteristics.

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“…In previous works we have measured the DOS of µc-Si:H samples from the modulated photoconductivity (MPC) method, both in the conventional trapping and release regime [7] and in the recombination regime (RR-MPC) [8,9]. We have found a correlation between the doping level of the samples and the subgap DOS.…”

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confidence: 92%

Density of States in Thin Boron-Doped Microcrystalline Silicon Films Estimated from the Thermally Stimulated Conductivity Method

2014

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In this work, a series of boron-doped microcrystalline silicon samples [µc-Si:H(B)] were deposited by plasma--enhanced chemical vapor deposition, using silane (SiH4) diluted in hydrogen, and diborane (B2H6) as a dopant gas. The concentration of B2H6 in SiH4 was varied in the range of 0100 ppm. The density of states was obtained from the thermally stimulated conductivity technique and compared with results obtained by the modulated photoconductivity methods. To explain the poor agreement between the density of states obtained from the thermally stimulated conductivity and the other methods, it is shown by means of numerical simulations that the density of states is very sensitive to experimental errors introduced in the calculation of the µnτn product (mobility of electron × lifetime of the electron). The thermally stimulated conductivity method is applied here for the rst time to calculate the density of defect states in the forbidden band of µc-Si:H samples.

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Characterization of defect levels in semi-insulating 6H-SiC by means of photoinduced transient spectroscopy and modulated photocurrent technique

Cited by 9 publications

References 20 publications

Implications of Trap-Assisted Nongeminate Charge Recombination on Time- and Frequency-Domain Photocurrent Degradation Signatures of Organic Solar Cells

Implications of Trap-Assisted Nongeminate Charge Recombination on Time- and Frequency-Domain Photocurrent Degradation Signatures of Organic Solar Cells

Current status of modelling the semi-insulating 4H–SiC transient photoconductivity for application to photoconductive switches

Density of States in Thin Boron-Doped Microcrystalline Silicon Films Estimated from the Thermally Stimulated Conductivity Method

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