Determination Of Surface Recombination Velocity Research Articles

Determination of Surface Recombination Velocity From Current–Voltage Characteristics in SiC p-n Diodes

Surface recombination velocity on mesa sidewalls of SiC p-n diodes with various surface passivation conditions was evaluated from the device-size-dependent preexponential factor of recombination current ( ${J}_{\text {0rec}}$ ). The diodes passivated by SiO2 with postoxidation nitridation were dipped into HF to eliminate a shunt current, which is evoked by the nitrided SiO2 layer and disturbs the analysis of the recombination current. For accurate determination of the surface recombination velocity, an effective recombination zone width was precisely derived taking account of the distribution of carrier density in the depletion layer. The surface recombination velocity of the diodes without any passivation and with the postoxidation nitridation (NO annealing at 1250 °C for 70 min) was determined as $\text {1.2}\times \text {10}^{\text {7}}$ and $\text {6.0}\times \text {10}^{\text {5}}$ cm/s, respectively, which indicates that the postoxidation nitridation can reduce the surface recombination by a factor of about 20. We confirmed that TCAD simulation could reproduce the current–voltage characteristics by utilizing the extracted parameters. In addition, an evaluation method was proposed to determine the surface recombination velocity from the high-current region, where diffusion current is dominant.

Classical modelling of grain size and boundary effects in polycrystalline perovskite solar cells

A theoretical approach based on the Matthiessen rule for scattering lifetime is presented to formulate the effective characteristics of polycrystalline solar cells. Application of this method to Perovskite solar cells obtains polycrystalline bulk defect density for diverse grain sizes along with the determination of surface recombination velocity at grain boundaries. Unlike previous works on Silicon based solar cells that use an independently weighted average equation for extracting mobility, we introduce a variation of Drude-Smith model for calculating the mobility from carrier lifetime and defect density. In agreement with the experiments, introduced method reveals sub-picosecond background scattering times associated with phonon-lattice vibrations. Obtained carrier diffusion length spans over multi-micron to multi-millimeter scale for grain sizes ranging from 100 nm to 1 mm. Calculated monomolecular recombination lifetimes explains elevated Photoluminescence Yield and peak position in larger grain sizes. Presented method is verified by feeding extracted parameters into Drift-Diffusion equations and fitting with reported experimental photovoltaic conversion efficiency data. Finally, through employing a Gaussian distribution for grain sizes, we also study the reduction of device efficiency caused by non-uniform grain size distribution as a more realistic case.

Determination of Surface Recombination Velocities at Contacts in Organic Semiconductor Devices Using Injected Carrier Reservoirs.

A method to determine surface recombination velocities at collecting contacts in interface-limited organic semiconductor devices, based on the extraction of injected carrier reservoirs in a single-carrier sandwich-type structure, is presented. The analytical framework is derived and verified with drift-diffusion simulations. The method is demonstrated on solution-processed organic semiconductor devices with hole-blocking TiO_{2}/organic and SiO_{2}/organic interfaces, relevant for solar cell and transistor applications, respectively.

Determination of surface recombination velocities of organic monolayers on silicon through Kelvin probe

We report the determination of the surface recombination velocity of electron-hole pairs for silicon samples passivated with organic monolayers using the Kelvin probe. The recombination velocity was determined from the surface photovoltage and incident photon flux. By scanning of the Kelvin probe tip over the sample, the change in surface recombination velocity can be measured allowing recombination lifetime mapping. Organic monolayers with different chain lengths and exhibiting various recombination lifetimes were synthesized through a two-step chlorination-alkylation technique. The estimated recombination lifetimes were compared against those obtained from an industrial standard technique and were found to be in good agreement.

Surface recombination parameters of interdigitated-back-contact silicon solar cells obtained by modeling luminescence images

Current losses at surfaces play a crucial role in the optimization of high-efficiency silicon solar cells. We present a new approach to characterize the surface recombination activity of interdigitated-back-contact (IBC) silicon solar cells by comparing experimental and simulated photoluminescence images (PL). The different recombination properties of the p- and n-doped regions of IBC cells in combination with the operating condition lead to contrast profiles in the PL image that vary with bias voltage. We achieve a good matching of experimental and simulated data for the investigated cells enabling the analysis of how sensitive the simulated contrast patterns are to changes in the surface recombination at the emitter, back- and front-surface-field and if a better matching of the experimental PL images is possible. Using these PL images in combination with simulations around the open circuit voltage Voc the determination of surface recombination velocities S and emitter saturation currents J0 on finished cells is made possible for the first time. This approach also opens a new path towards loss analysis of finished PERL, PERC, MWT and other silicon solar cells.

Determination of surface recombination velocity so and carrier lifetime τo from IF(VG) characteristics of Al/PECVD-SiNx/pn-GaAs gated diodes

Investigations on Al/SiNx/pn-GaAs gated diodes reveal that the forward current IF in the recombination current region consists of a bulk current part being generated in the depletion region of the metallurgical p–n junction, and a surface recombination current part occurring at the intersection plane of this depletion region with the semiconductor surface. A variation of the gate length influences neither surface current nor HF capacitance of the p–n junction. However, the surface current can be controlled by the gate bias. A simple model using surface recombination at the junction perimeter enables evaluation of surface recombination velocity so and carrier lifetime τo in the depletion region of the p–n junction. Thus the 2kT recombination current of the gated diodes can be separated into a surface and a bulk part. This method can also be applied to other AIIIBV semiconductors.

Nitridation by NO Or N2O of Si-SiO2 Interfaces

ABSTRACTX-ray photoelectron spectroscopy (XPS) and photocurrent measurements for the determination of surface recombination velocity provide complementary information on the structure of the Si-SiO2 interface, being sensitive to the chemical nature of foreign species at the interface the former, and to intrinsic defects the latter. The comparison of the XPS N(1s) peaks determined for the Si-Si0 2 interfaces nitrided in NO or N2O ambients is useful to identify the species responsible for the broadening of the peak. In fact, nitridation by NO is mainly responsible for the formation of Si3N moieties at the silicon surface in which silicon atoms are partially oxidized; while nitridation by N2O proceeds with the oxidation of Si – Si backbonds to Si – N bonds, thus resulting in the formation of N(Si(O-)3)3 groups embedded in the oxide. Surface recombination velocity by photocurrent measurements gives evidence that nitridation in N2O is associated with an appreciable co-oxidation, while nitridation in NO is mainly associated with the passivation of interface states. Furthermore N2O and NO nitridation are responsible for different morphologies of the nitrided layers.

Determination of surface recombination velocity and bulk lifetime in detector grade silicon and germanium crystals

The utility of a noncontact photoconductive decay (PCD) technique is demonstrated in measuring the bulk lifetime, /spl tau//sub B/, and surface recombination velocity, S, in detector grade silicon and germanium crystals. We show that the simple analytical equations which relate the observed effective lifetimes in PCD transients to /spl tau//sub B/ and S have a limited range of applicability. The noncontact PCD technique is used to determine the effect of several surface treatments on the observed effective lifetimes in Si and Ge. A degradation of the effective lifetime in Si is reported as a result of the growth of a thin layer of native oxide at room temperature under atmospheric conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Determination of surface recombination velocity of excess carriers in amorphous silicon using the SSPG technique

The steady state photocarrier grating (SSPG) technique is used to determine the surface recombination velocity in a-Si:H without changing the wavelength of the light producing the photocarriers. This method requires knowledge of the absorption coefficient and the ambipolar mobility of the carriers. In a-Si-:H, the surface recombination velocity is determined by this method to be about 100 cm/s.

ELECTRONIC TRANSPORT PROPERTIES CHARACTERIZATION OF SILICON WAFERS BY MODULATED PHOTOREFLECTANCE

We have used the photoreflectance technique to characterize electronical transport properties of silicon wafers. By using the intermediate frequency range (1 kHz to 100 kHz) and selecting a proper excitation wavelength, it is possible to facilitate the characterization. In particular we show that this technique permits the determination of surface recombination velocity.

Determination of surface recombination velocity in semiconductor layers by light excitation of Schottky barriers

An analytical expression for the current induced by a monochromatic light source in a Schottky diode, illuminated from the back is derived. Comparison of theory and experiment for the dependence of the induced current on the optical absorption coefficient of the material is possible to provide values for the surface recombination velocity.

Surface and interface recombination in thin film HgCdTe photoconductors

A method is described for the separation of bulk and surface recombination parameters using experimentally measured photoconductive decay curves. Curve fitting procedures using numerical solutions to the time dependent hole continuity equation permit a unique determination of surface recombination velocities and bulk lifetime. The method is applied to thick and thin films of HgCdTe to determine recombination velocities at several technologically important interfaces. Values of recombination velocity ranged from 300 to 20 000 cm/s depending upon material growth method and surface preparation. Experimentally observed deviations from the assumed model are discussed in terms of a spatially dependent bulk lifetime.

Determination of surface recombination velocity at a grain boundary using electron-beam-induced current

In order to determine the surface recombination velocity at a grain boundary surface, computer-aided calculations of the theoretical electron-beam-induced-current response to a point source excitation are fitted to data taken as a function of distance from the grain boundary. It is demonstrated that the data is in good agreement with this theoretical response for distances greater than two maximum penetration depths of the incident electron beam.

The importance of the excitation volume in determination of surface recombination velocity

A Simple approach for evaluating the electron-beam induced current (EBIC) response of a grain boundary in polycrystalline silicon demonstrates that the response is composed of two different responses. At distances greater than two excitation-volume radii from the grain boundary, the response yields an effective surface recombination velocity within about ten percent of that obtained by fitting the data to the theoretical response for a point-source excitation. However, at distance less than two excitation-volume radii, the grain-boundary response is demonstrated to be the response to a skewed Gaussian excitation. This exemplifies the limitations of spacial resolution of an electron probe and the importance of quantitative measurements in determining the effective surface recombination velocity of internal and external surfaces of semiconducting regions.

Application of scanning electron microscopy to determination of surface recombination velocity: GaAs

A method is reported for the determination of the surface recombination velocity by scanning electron microscopy; this method is based on an established relationship between the effective diffusion length of the minority carriers, the penetration depth of the electron beam, and the surface recombination velocity. Values of surface recombination velocity, up to about 2.5×106 cm/sec were determined in n-type GaAs with a bulk minority-carrier lifetime of the order of 10−8–10−10 sec; in GaAs, with carrier concentrations exceeding 1018 cm−3, recombination velocity of about 3×106 cm/sec represents a saturation value.

On the determination of surface recombination velocity from the transient response of MIS structures

Abstract : ZERBST has developed a method of measuring both minority carrier lifetime and surface recombination velocity from the transient response of MIS capacitors to a depleting pulse when the capacitors are initially biased in the inversion region. This method is based on an equation relating the rate of change of the capacitance C of the MIS structure, the lifetime pi and the surface recombination velocity s. The report discusses technique for handling the experimental data that can simplify the necessary computation and partially automate the measurements of lifetime and surface recombination velocity.

High-field effects in photoconducting cadmium sulphide

High-field characteristics of the photocurrent in CdS are studied by the use of pulse techniques and blocking electrodes. This method enables the determination of surface recombination velocities and bulk trapping times for both electrons and holes. Under special surface conditions, the measurements yield direct information on the electron transport properties at high fields. Of particular interest is the conclusion that the electron drift velocity is linear up to a field of at least 8 × 10 4 V cm , at which field it attains the value of $ ̃ 10 7 cm sec . The implications of this result in terms of the energy dissipation mechanism in CdS are briefly discussed. The technique described can also be applied to low-resistivity semiconductors.