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Simplified image describing the position of shallow and deep levels in the band gap of a semiconductor. Note the more extended nature of shallow levels, in contrast with the more localized nature of deep levels. E C and E V are the conduction band and valence band energy,
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Several nitrogen containing III-V compound semiconductors, together with GaInAs and AlGaAs, were electrically characterized. The main technique used was deep level transient spectroscopy (DLTS), but also current voltage (I-V), capacitance voltage (C-V), isothermal transient spectroscopy (ITS) and Hall measurements were employed. As a contribution t...
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... the analysis techniques developed, as well, it was realized that other energy levels, in both simple and compound semiconductors, are present. They are neither close to the conduction nor the valence band, i.e., closer to the middle of the band gap, thus, they are called deep levels ( Fig 1). respectively. ...
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... this work, the use of inductors to improve the data acquisition by DLTS has been researched. The general electrical model for a Schottky contact is shown in Fig. 10. The series model of Fig. 11 a) is preferred, because this makes it possible to regard the capacitance and resistance measured in DLTS directly as those of the Schottky contact 40 . It has been shown that the series capacitance C S and the series resistance R S (Fig. 11 a)) are related to the parallel capacitance C P and parallel ...
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... this work, the use of inductors to improve the data acquisition by DLTS has been researched. The general electrical model for a Schottky contact is shown in Fig. 10. The series model of Fig. 11 a) is preferred, because this makes it possible to regard the capacitance and resistance measured in DLTS directly as those of the Schottky contact 40 . It has been shown that the series capacitance C S and the series resistance R S (Fig. 11 a)) are related to the parallel capacitance C P and parallel resistance R P through ...
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... researched. The general electrical model for a Schottky contact is shown in Fig. 10. The series model of Fig. 11 a) is preferred, because this makes it possible to regard the capacitance and resistance measured in DLTS directly as those of the Schottky contact 40 . It has been shown that the series capacitance C S and the series resistance R S (Fig. 11 a)) are related to the parallel capacitance C P and parallel resistance R P through ...
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... Q = R S C S w is the quality factor of the series circuit (Fig. 11 a)) and w is the frequency of the drive signal delivered by the capacitance ...
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... capacitance meter measures the capacitance of the parallel circuit (Fig. 11 b)). Usually, it is supposed that the Schottky contact only shows a capacitive nature 11 , i.e., R S = 0. Under this assumption Q = 0 and then C P = C S . Broniatowski et. al have suggested that the effect of a properly chosen inductance in series with the Schottky contact might increase the signal-to- noise ratio 41 . In publication I, ...
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... another application for inductors was found (publication II). If an inductance L X is attached in series with a Schottky contact (Fig. 11 c)), the resulting series circuit is equivalent to the original series model of a Schottky contact (Fig. 11 a)), if one assumes a new series capacitance C' S ( Fig. 11 d)) given ...
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... another application for inductors was found (publication II). If an inductance L X is attached in series with a Schottky contact (Fig. 11 c)), the resulting series circuit is equivalent to the original series model of a Schottky contact (Fig. 11 a)), if one assumes a new series capacitance C' S ( Fig. 11 d)) given ...
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... another application for inductors was found (publication II). If an inductance L X is attached in series with a Schottky contact (Fig. 11 c)), the resulting series circuit is equivalent to the original series model of a Schottky contact (Fig. 11 a)), if one assumes a new series capacitance C' S ( Fig. 11 d)) given ...
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... variations in R S at high temperature are attributable to an inductance effect from the ohmic contact 42 ) as predicted by Eq. 39. But mainly, R S is far from being zero, particularly at low temperatures. This has a deep impact on data obtained from the DLTS scan, as the quality factor becomes non-negligible (Q > 1) as the temperature decreases ( Fig. 13). The parameter Q shows some interesting features: it is independent of the inductance, as expected; it increases as the temperature decreases, being bigger than 1 below 160 K, and almost 5 at 100 K. If C S were considered to be the same as the measured C P read from the capacitance meter and were not corrected for Q ≠ 0, an error of an ...
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... the DLTFS and ITS study, the samples were reverse biased at -0.7 V. The pulse bias was 0 V. The DLTFS curves and the respective Arrhenius plots are shown in Fig. 14 a) and b), Fig. 14 b). The Arrhenius plot of the ITS measurements can be seen in Fig. 15. The DLTFS and ITS studies yield the activation energies of 0.58 eV, 0.55 eV and 0.27 eV for peaks A, B and C, respectively, in the as-grown sample. The evolution of the activation energy and density of the three traps as a function of annealing ...
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... the DLTFS and ITS study, the samples were reverse biased at -0.7 V. The pulse bias was 0 V. The DLTFS curves and the respective Arrhenius plots are shown in Fig. 14 a) and b), Fig. 14 b). The Arrhenius plot of the ITS measurements can be seen in Fig. 15. The DLTFS and ITS studies yield the activation energies of 0.58 eV, 0.55 eV and 0.27 eV for peaks A, B and C, respectively, in the as-grown sample. The evolution of the activation energy and density of the three traps as a function of annealing temperature can be seen ...
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... the DLTFS and ITS study, the samples were reverse biased at -0.7 V. The pulse bias was 0 V. The DLTFS curves and the respective Arrhenius plots are shown in Fig. 14 a) and b), Fig. 14 b). The Arrhenius plot of the ITS measurements can be seen in Fig. 15. The DLTFS and ITS studies yield the activation energies of 0.58 eV, 0.55 eV and 0.27 eV for peaks A, B and C, respectively, in the as-grown sample. The evolution of the activation energy and density of the three traps as a function of annealing temperature can be seen in This behavior and comparison with the literature strongly ...
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... (100) For the as grown sample, only one peak is seen (peak A) around 375 K. The data in the Arrhenius plot (Fig. 18 b)) become more scattered as the annealing temperature ...
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... were annealed at 1050 o C for 10 min under hydrogen flow. After that, they were nitridated in NH 3 at 1050 o C for 30 min. Subsequently, the temperature was decreased to the growth temperature between 550 o C and 650 o C and the carrier gas was switched from H 2 to N 2 . The growth rate of InN as a function of TMIn molar flow is shown in Fig. 19. There is a linear dependence of the growth rate on the TMIn flow in the studied temperature ...
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Citations
... The iterative cycles proposed in [24] are used in solar cell parameters of curve JV in figure 5(a) in [23] to try to reobtain the solar cell parameters. Briefly, they consist of the iterative application of the Cheung et al method [27][28][29][30][31][32], with procedures A and B proposed in [6,7]. [3], for the C sample in [3] and ArOF in [33], respectively. ...
... The solar cell parameters for Ar, Ar-Freon, Ar-O-Freon and N-O-Freon, both in the darkness and illumination case, were obtained in [15], where the iterative cycles proposed in [24] are applied, and they are further discussed there. Briefly, they consist of the iterative application of the Cheung method [27][28][29][30][31][32], with procedures A and B proposed in [6,7]. ...
In this Part 2 of these series of articles, a discussion of the literature reported obtention of the solar cell parameters (the shunt resistance ( R sh ), the series resistance ( R s ), the ideality factor ( n ), the light current ( I lig ), and the saturation current ( I sat )), via the use of the Co-content function CC(V,I) = ∫ 0 V ( I-I sc ) dV (where I sc =I ( V =0) ) is given. The results reported in Part 1, namely, the accuracy dependence of the determination of R sh , R s , n , I lig , and I sat , as function of the number of measured points per voltage ( P V ) and percentage noise ( p n ) is used to analyse the reported solar cell parameters. In one case, the application of CC(V,I) to solar panels is discussed, revealing that it can also be used in the case of solar panels, and not only for laboratory-made solar cells, in voltage ranges larger than [0 V, 1 V]. In another case, the application of CC(V,I) to IV curves showing the roll-over effect is discussed. It is found that the roll-over effect has a pernicious effect in the solar parameter extraction, and then the CC(V,I) should be calculated before the roll-over effect takes place. In a third case, the importance of the correct determination of I sc on the correct calculation of CC(V,I) is discussed.
... Equations (3) and (4) are both mathematically similar to the Schottky equation [21,22]. Some authors have mentioned that they used the Cheung method to obtain their solar cells parameters [23][24][25]. ...
A new proposal for the extraction of the shunt resistance (Rsh) and saturation current (Isat) of a
current-voltage (I–V) measurement of a solar cell, within the one-diode model, is given. First,
the Cheung method is extended to obtain the series resistance (Rs), the ideality factor (n) and an
upper limit for Isat. In this article which is Part 1 of two parts, two procedures are proposed to
obtain fitting values for Rsh and Isat within some voltage range. These two procedures are used in
two simulated I–V curves (one in darkness and the other one under illumination) to recover the
known solar cell parameters Rsh, Rs, n, Isat and the light current Ilig and test its accuracy. The
method is compared with two different common parameter extraction methods. These three
procedures are used and compared in Part 2 in the I–V curves of CdS-CdTe and CIGS-CdS solar
cells.
... The QW levels were populated by applying pulses of the forward voltage of +1 V for 100 ns. These conditions give the following advantages: (i) DLTS measurements are not distorted by a large value of the series resistance [26,27], (ii) no DLTS signal appears from the interface epilayer/substrate, as the depletion region never reaches this interface, (iii) DLTS scans are not affected by any leakage current [28][29][30]. ...
... The samples containing Sn reveal downward DLTS peaks. These peaks are attributed to the majority carrier traps (holes in this study) [28]. These traps are associated to the emission of holes from ground heavy hole states of the embedded SiSn QWs. ...
... Otherwise, for non-gaussian DLTS spectrum, deconvolution is necessary, as it is the case in this study for sample S2. If only the ground level of a QW contributes to the gaussian DLTS signal (as it is the case in this study for samples S3 and S4, further details are given below), then the maximum or minimum of the DLTS signal at a temperature (T) gives the activation energy (E act ) of this level according to equation (1) [16,28,30]: ...
A set of Si1-xSnx/Si(001) quantum wells is grown by applying molecular beam epitaxy. The activation energies of holes in these quantum wells are studied by deep-level transient spectroscopy. It is observed that the holes activation energies increase monotonically with the Sn fraction (x). The valence band offset between pseudomorphic Si1-xSnx and Si obeys the dependence ∆E_v = 1.69x eV, while the offset between the average valence bands of unstrained Si1-xSnx/Si heterojunction was deduced and obeys the dependence ∆E_(v_av )= 1.27x eV.
... The QW levels were populated by applying pulses of the forward voltage of +1 V for 100 ns. These conditions give the following advantages: (i) DLTS measurements are not distorted by a large value of the series resistance [26] [27], (ii) no DLTS signal appears from the interface epilayer/substrate, as the depletion region never reaches this interface, (iii) DLTS scans are not affected by any leakage current [28] [29] [30]. ...
... The samples containing Sn reveal downward DLTS peaks. These peaks are attributed to the majority carrier traps (holes in this study) [28] ...
... The usual C −2 versus V analysis [32] can also be used for MOS structures in the depletion region. In this case, using equation (1), the expression of C −2 Tot is given by ...
... , is also shown in figure 5. L D characterizes the depth resolution of the CV doping profile technique [32]. The obtained parameters will be used in the subsequent analysis below. ...
The negative differential capacitance (NDC) effect is observed on a titanium–oxide–silicon structure, formed on n-type silicon with embedded germanium quantum dots (QDs). The Ge QDs were grown by an Sb-mediated technique. The NDC effect was observed for temperatures below 200 K. We found that approximately six to eight electrons can be trapped in the valence band states of Ge QDs. We explain the NDC effect in terms of the emission of electrons from valence band states in the very narrow QD layer under reverse bias.
In this article, the solar cell parameters (within the one-diode solar cell model) are obtained with less than 10 % error, integrating the Co-Content function using up to order 6 Simpson integration method, and as a function of the number of measured points per volt and a percentage noise of the maximum current. It is shown, that less than 10 % error (in some cases around 1 %) can be obtained, in case the percentage noise is as larger as 0.1 %, using higher order Simpson integration than 1, the usually used trapezoidal integration method.
La principal fuente de energía en satélites y sondas espaciales es la provista por el Sol a través de la conversión fotovoltaica de sus paneles solares. Por este motivo es crucial, por un lado, garantizar la durabilidad de las celdas solares durante el tiempo previsto en la misión y, por otro, aumentar su eficiencia debido al continuo incremento de la demanda de energía eléctrica de sus instrumentos. El Departamento Energía Solar (DES) de la Comisión Nacional de Energía Atómica de Argentina (CNEA) realiza actividades de investigación y desarrollo relacionadas con el aprovechamiento de la energía solar mediante conversión fotovoltaica para aplicaciones espaciales y terrestres. La presente tesis, realizada en el DES, tiene como objetivo general cubrir la necesidad de contar con una técnica que caracterice la estructura de los defectos presentes en los semiconductores que constituyen las celdas solares, como una herramienta adicional para evaluar y predecir el daño producido por la radiación espacial sobre éstas, ya que causa la degradación de su prestación. En este marco, resulta fundamental conocer el comportamiento de los dispositivos al ser sometidos a experimentos de daño por radiación con dosis acordes con la órbita y la duración de cada misión particular, para así realizar el correcto dimensionamiento de los paneles solares.
Dado que se desconoce el efecto de cada tipo de defecto producido por la radiación en la prestación de las celdas solares, el objetivo particular del presente trabajo es determinar experimentalmente la estructura de defectos electrónicamente activos producida en los dispositivos bajo estudio antes y después de las experiencias de daño por radiación utilizando la técnica Deep Level Transient Spectroscopy (DLTS).
Para ello se repasó la fenomenología física involucrada en la conversión fotovoltaica de la energía solar, la descripción del ambiente espacial, y el efecto producido por la radiación en los materiales semiconductores.
Además, se estudiaron los principios básicos que regulan el funcionamiento de la técnica DLTS, particularmente las propiedades de la capacidad de la juntura semiconductora y cómo se ve afectada en presencia de defectos. A partir de esto se estudió su aplicación experimental y el análisis necesario para determinar la energía de activación, la sección de captura y la densidad de los defectos a partir de los resultados experimentales.
Utilizando este conocimiento se implementó la técnica en el DES. Dado que no se contaba con desarrollos previos, se repasaron las condiciones técnicas para su implementación, se realizaron desarrollos de hardware y software, y finalmente se realizó la puesta a punto del sistema y su validación.
Con la implementación de la técnica DLTS finalizada, se realizaron experimentos de daño por radiación con protones de 10 MeV en el acelerador de iones pesados TANDAR de la CNEA sobre sensores solares de silicio fabricados en el DES. Estas experiencias fueron diseñadas y realizadas específicamente para aplicar la técnica DLTS con el desarrollo implementado. Se realizaron caracterizaciones de las muestras antes y después de las irradiaciones, utilizando técnicas previamente implementadas en el DES, que mostraron la degradación de los sensores a medida que aumentaba la fluencia de la irradiación. Finalizadas las irradiaciones se realizaron las mediciones y análisis de DLTS, arrojando como resultado la energía de activación, la sección de captura y la densidad para cada fluencia estudiada de cada tipo de defecto provocado por la radiación.
Por otra parte se realizaron cálculos numéricos de la capacidad, tanto estacionaria como transitoria, de junturas semiconductoras con defectos introducidos a priori a fin de simular la aplicación de la técnica DLTS. La introducción de mejoras originales en el modelo analítico normalmente utilizado, que incluyeron la eliminación de aproximaciones y la incorporación de modelos físicos de las propiedades electrónicas, permitió refinar el análisis de los resultados experimentales, estudiar los errores provocados por las condiciones experimentales sobre el cálculo de las características de los defectos, así como mejorar, en algunos casos, el ajuste de dichos resultados.
Por último, en base a las simulaciones y las características del equipo desarrollado, se propuso como trabajo futuro mejorar el control térmico a fin de aumentar la resolución en temperatura del dispositivo experimental, ya que ésta es la variable más importante para reducir el error experimental. Por otro lado se propone seguir trabajando en la mejora del modelo teórico de la capacidad con la perspectiva de perfeccionar la fidelidad en la reproducción de los espectros experimentales y, consecuentemente, la extracción de los parámetros de los defectos.
In this Part 2 of these series of articles, the procedure proposed in Part 1, namely a new parameter extraction technique of the shunt resistance (Rsh) and saturation current (Isat) of a current-voltage (I-V) measurement of a solar cell, within the one-diode model, is applied to CdS-CdTe and CIGS-CdTe solar cells. First, the Cheung method is used to obtain the series resistance (Rs) and the ideality factor n. Afterwards, procedures A and B proposed in Part 1 are used to obtain Rsh and Isat. The procedure is compared with two other commonly used procedures. Better accuracy on the simulated I-V curves used with the parameters extracted by our method is obtained. Also, the integral percentage errors from the simulated I-V curves using the method proposed in this study are one order of magnitude smaller compared with the integral percentage errors using the other two methods.
This chapter focuses on photoconductivity (PC) and transient
spectroscopy techniques including photo-induced transient spectroscopy
(PITS) and deep-level transient spectroscopy (DLTS). Spectral
photoconductivity provides a powerful tool for measuring the band-gap
energy and optical transitions in semiconductors. On the other hand,
transient photoconductivity can be used to determine the time constants
associated with specific recombination processes. PITS and DLTS are
extensively used to characterize deep energy levels due to traps. The
aim of this chapter is to discuss the fundamentals of these measurement
techniques and describe typical experimental setups and methods of
analysis for the determination of important trap parameters, such as the
activation energy, the carrier capture cross-section, and the trap
density.
The deep level transient spectroscopy technique is used on a Ti Schottky diode on n-Si with embedded Ge quantum dots (QDs) obtained by Sb-mediated growth. We discover an electron trap and two hole traps within the Si band gap at the plane of the Ge QDs. The electron trap has an activation energy of 87 ± 7 meV. One hole trap has an activation energy of 304 ± 32 meV, The second hole trap is represented by an energy sub-band between 125 and 250 meV above the top of the Si valence band. The electron level (87 ± 7 meV) and the hole energy sub-band (125–250 meV) are identified as energy levels of the Ge QDs array. The deepest trap level for holes (304 meV) has not been identified yet.
