Studies of diffused phosphorus emitters: saturation current,surface recombination velocity, and quantum efficiency

The surface recombination velocity s for silicon surfaces passivated with thermal oxide was experimentally determined as a function of surface phosphorus concentration for a variety of oxidation, anneal, and surface conditions. This was accomplished by measuring the emitter saturation current density J₀ of transparent diffusions for which the J₀ is strongly dependent on s. At the lowest doping levels, the value of s was confirmed by measurements of s on substrates with uniform phosphorus doping. The impact of these measurements on solar cell design is discussed     

Optimization of saturation current density of PECVD SiN coated phosphorus diffused emitters using neural network modeling

Emitter surface passivation by low temperature plasma enhanced chemical vapor deposition (PECVD) silicon nitride is investigated and optimized in this paper. We have found that the saturation current density of a 90±10 μ/sq phosphorus diffused emitter with N_s ≈3 x 10¹⁹ and X_j ≈0.3 μm can be lowered by a factor of eight by appropriate PECVD silicon nitride deposition and photoassisted anneal. PECVD silicon nitride deposition alone reduces the emitter saturation density (J_oe) by about a factor of two to three, and a subsequent photoanneal at temperatures ≥350°C reduces J_oe by another factor of three. In spite of the larger flat band shift for direct PECVD silicon nitride coating, the silicon nitride induced surface passivation is found to be about a factor of two inferior to the thermal oxide plus PECVD silicon nitride passivation due to higher interface state density at the SiN/SiO₂ interface compared to SiO₂/Si interface. A combination of statistical experimental design and neural network modeling is used to show quantitatively that lower radio frequency power, higher substrate temperature, and higher reactor pressure during the PECVD deposition can reduce the J_oe of the silicon nitride coated emitter.     

Studies of implanted boron emitters for solar cell applications

B implanted emitters are investigated in the back junction cell configuration and their material properties are tested in double side implanted Si wafers. B has been implanted at 5 keV at various dose conditions varying from 1 × 10¹⁴ up to 3 × 10¹⁵ at./cm² and activated at 1000°C for 10 min. N‐type 8 × 8 cm² mono‐crystalline cells are fabricated and measured. Both fill factor and efficiency increase for high‐B doses. However, at 10¹⁵ at./cm² B dose the V_oc drops, which is in agreement with lifetime degradation in the wafer. Defect evolution simulations of B_nI_m clusters formation is correlated with lifetime degradation. Copyright © 2011 John Wiley & Sons, Ltd.     

Measurement of diffusion length, lifetime, and surface recombination velocity in thin semiconductor layers

A small-signal admittance method is developed for the determination of two important parameters affecting the performance of several semiconductor devices with thin layers such as I²L and MOS transistors, OCI-HLE, BSF and TJ solar cells. These parameters, the minority-carrier diffusion length (or the minority-carrier lifetime) and the surface recombination velocity, are found using a combination of low-frequency and high-frequency admittance measurements. The theoretical base of the method and experimental results showing its application and usefulness are presented.     

Evidence for 1/f noise in diffusion current due to insulator trapping and surface recombination velocity fluctuations

In this paper, we present evidence for 1/f noise in diode diffusion current due to fluctuations in surface recombination velocity caused by insulator trapping. Using a unique structure consisting of a thin HgCdTe film with a pn junction on one side and an insulated gate on the other, we demonstrate that the noise measured in the junction is a strong function of the surface potential on the opposite side of the film. We compare the results to model predictions, finding good qualitative agreement.     

A model for surface recombination velocity and lifetime ofsemiconductor lasers

A simple and powerful relationship is presented for estimating the lifetime of continuous-wave (CW) diode lasers. Accelerated aging tests can directly be translated into the relationship. A model for the surface recombination velocity is developed based on the physical and chemical phenomenon governing the change of the surface recombination velocity. This model, together with a criterion for no thermal runaway developed earlier, is used to arrive at the simple relationship. The relationship provides a physical basis for estimating the lifetime     

Determination of diffusion length and surface recombination velocity by light excitation

The current induced by a monochromatic light source in a Schottky barrier or p?n junction perpendicular to the sample surface is analyzed. Expressions for the induced current are derived for a scanning light spot and for uniform illumination with part of the sample shadowed. A uniform illumination induces a current that is more nearly an exponential function of the distance between the junction and the illuminated area than a moving spot. When the effect of surface recombination is strong, an alternative method of deducing the diffusion length from the measured current is suggested. The surface recombination velocity may be determined from the dependence of the collected current on the optical penetration depth in a simple manner.     

利用二次阳极氧化方法降低N型碲镉汞材料表面复合速度

利用微波反射光电导衰退法比较了采用一次阳极氧化和二次阳极氧化的N型碲镉汞材料的非平衡载流子寿命及其随温度的变化,通过与理论值进行比较拟合得到了碲镉汞材料表面复合速度随温度的变化曲线.结果发现,二次阳极氧化方法能够更好地降低材料表面悬挂键的密度,同时减少抛光引入的表面缺陷能级的数量,从而降低材料的表面复合速度,改善材料的非平衡载流子寿命,利于制造出高性能的HgCdTe红外探测器.     

Comparison of Thai''s theory with experimental boron doping profiles in silicon, diffused from boron nitride sources

Silicon wafers, (111)-oriented, were diffused with BN sources at temperatures form 986 to 1132°C and times from 15 min to 4 hr at various flow rates of ambient gas (N₂) of 2–80 1/hr. Doping profiles were determined. They showed plateaus of nearly constant doping concentration near the silicon surface and great deviations from erfc profiles. From this profiles diffusion coefficient D(c) was derived by means of Boltzmann's method as a function of doping concentration C. Comparison with Thai's theory (corrected by Jain and van Overstraeten) shows for the nondegenerate case of field-enhanced diffusion good agreement with the experimental results of D(c). A remarkable increase for D(c) is found for boron concentrations C≥10¹⁹ cm⁻³. Preexponential term D₀ activation energy E_A for diffusion coefficient D(c) are derived and found to be 1.36 cm²/sec and 3.59 eV respectively. They coincide well with values given by other authors.     

Determination of minority-carrier lifetime and surface recombination velocity with high spacial resolution

Quantitative analysis of the electron beam induced current in conjunction with high-resolution scanning makes it possible to evaluate the minority-carrier lifetime three dimensionally in the bulk and the surface recombination velocity two dimensionally, with a high spacial resolution. The analysis is based on the concept of the effective excitation strength of the carriers which takes into consideration all possible recombination sources. Two-dimensional mapping of the surface recombination velocity of phosphorus-diffused silicon diodes is presented as well as a three-dimensional mapping of the changes in the minority-carrier lifetime in ion-implanted silicon.     

On surface recombination velocity and output intensity limit of pulsed semiconductor lasers

Relationships obtained by F. Kappeler et al. (1982) are utilized to assess the effect of facet passivation on the output intensity limit in terms of surface recombination velocity. The results show a trend that the output intensity limit increases in an exponential manner with decreasing recombination velocity once the velocity is reduced by a factor of 2 from that for an unpassivated laser. They also indicate that the output intensity is not likely to be limited by nonradiative recombination at the facet when the recombination velocity is reduced by a factor of 4.<>     

Surface state and surface recombination velocity characteristics of Si-SiO2interfaces

A new device has been used to study the surface recombination velocity and surface state characteristics of Si-SiO2interfaces. The device consists of an epitaxially-formed junction diode. When the junction is forward-biased, minority carriers are injected from the heavily-doped substrate into the lightly-doped epitaxial region. The thickness of the epitaxial region is much less than the diffusion length for minority carriers. Thus, the diode current for a given junction forward bias is directly proportional to surface recombination velocity at the Si-SioO2interface. A gate electrode over the SiO2has been included to vary surface potential. Thus, this new device permits one to simultaneously study MOS capacitance-voltage characteristics as well as surface recombination velocity. The capacitance-voltage characterics indicate the surface states exhibit a quasi-continuous energy distribution. N-type surfaces exhibited donor levels lying in the range of ∼0.15 to ∼0.45 eV above the valence band; their density was found to vary from ∼5 × 10¹²to 5 × 10¹³states/cm²/eV. In contrast, p-type surfaces exhibited acceptor levels lying in the range of ∼0.15 to ∼0.45 eV below the conduction band; their density was comparable to those observed on n-type surfaces. The maximum value of surface recombination velocity was found to vary from 3 × 10³to > 10⁴cm/s. Surface recombination velocity was found to correlate directly with surface state density.     

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.     

Excess carrier cross-sectional profiling technique for determination of the surface recombination velocity

This paper presents a modified excess carrier profiling technique using carrier decay cross-sectional scans of wafers using a narrow excitation fiber guided beam and by using infrared light as well as microwave probes. The theoretical principles of the technique are based on the analysis of the depth variation of decay shape and the amplitude.     

Small-signal characteristics of a read diode under conditions of field-dependent velocity and finite reverse saturation current

Memristive one-port device modeling of a Read diode, taking into account of the field-dependent velocity and the finite reverse saturation current, is presented. Small-signal characteristics, equivalent circuit and diode impedance are obtained. Degradation and improvement of performance are discussed.     

Analysis of three-grating coupled surface emitters

Results of a grating-coupled surface emitter (GSE) analysis and a confirming experiment are reported. The GSE consists of two gain sections and three gratings sections that are not necessarily identical. The second-order gratings act both as distributed Bragg reflectors and output couplers via radiation. Thresholds of longitudinal modes are calculated for a symmetrical structure as a function of the two gain section pumping currents, and, for various combinations of pump currents, the near and far fields are compared. The theory is shown to agree qualitatively with an experiment     

Measurement circuits for silicon-diode and solar-cell lifetime andsurface recombination velocity by electrical short-circuit current decay

Two improved switching circuits for transient electrical short-circuit decay are presented that allow more accurate determination of base-region minority-carrier lifetime and back-surface recombination velocity of silicon p-n junction solar cells and diodes. In one circuit, metal-oxide-semiconductor transistors replace the bipolar switching circuit used in the original implementation of the method as described by T.W. Jung, et al. (ibid., vol.ED-31, p.588, 1984). In the other circuit, a pulse generator directly excites the device under study. Comparison of the two circuits by illustrative measurements shows that, in comparison to the original implementation of the method, these versions allow measurement of shorter effective lifetimes, such as those characteristic of low-resistivity (about 0.1 Ω-cm) silicon solar cells     

Carrier recombination at grain boundaries and the effective recombination velocity

The recombination of excess minority carriers at grain boundaries, or other interfaces with space-charge regions, is treated theoretically for general energy distributions of interface states (recombination centers). The distinction is made between minority carrier recombination velocity at the (grain-boundary) interface itself, and the effective recombination velocity for the collection of these carriers by the adjacent space-charge region. Calculations of the effective recombination velocity are made, as a function of the excess minority-carrier concentration at the edge of the space-charge region, since this is the quantity of most convenience for device modelling.