Temperature dependence of open-circuit photovoltage of a back-surface field semiconductor junction

Temperature dependence of the open-circuit photovoltage of a back surface field, diffused silicon junction has been studied analytically, including the effect of bandgap narrowing in the heavily doped back surface region. Open circuit voltage of a BSF structure has been found to be slightly less dependent on temperature as compared with that of a conventional cell. Further, the behaviour of a BSF cell is found to be relatively insensitive to base layer resistivity. These results support the experimental data published by some investigators on temperature dependence of solar cells.     

Theory of back surface field silicon solar cells

Back surface field silicon solar cells with n⁺pp⁺ (or sometimes p⁺nn⁺) structures are found to have better characteristics than the conventional solar cells. The existing theories have not been able to satisfactorily predict the experimentally observed parameters on these cells. A theory, based on the transport of both minority and majority carriers under the charge neutrality condition, has been developed in the present paper which explains the behavior of the back surface field solar cells. Good agreement is achieved between the results obtained by using this theory and the experimental observations of earlier workers.     

Saturation of photovoltage and photocurrent in p-n junction solar cells

Expressions for the photovoltage and photocurrent of a strongly illuminated p-n junction solar cell are derived by solving the ambipolar diffusion equation. A complete boundary condition is derived for the junction, which is valid for all levels of injection. In the open-circuit case, results are in agreement with those given by earlier theories, while in the short-circuit case, the current is found to saturate at the ratio of the diffusion potential to the internal resistance. Results are used to explain the experimental results of earlier workers.     

On the surface photovoltaic effect in a multivalley semiconductor in an external magnetic field

A theory of the photovoltaic effect in a semi-infinite multvalley semiconductor upon the absorption of polarized light at free carriers caused by the specular reflection and diffuse scattering of electrons at a film surface is developed by us. The kinetic Boltzmann equation in the approximation of time relaxation and boundary conditions, which determine the correlation between the distribution function of electrons reflected from a semi-infinite crystal surface and the distribution function of electrons incident onto a surface for the case of both specular reflection and diffuse scattering is used. The aforementioned takes into account the fact that the distribution function of electrons diffusely scattered from a surface depends only on their energy and is determined from the condition of total electron flux vanishing at the surface. Expressions for analyzing the spectral dependence of the current which is linearly dependent on the magnetic-field strength are obtained.     

The spectrum of intermodulation generated in a semiconductor diode junction

In this paper exact formulas are found for the intermodulation generated in a semiconductor diode junction, and a method is developed to make the calculation of the intermodulation practicable. This method generates the intermodulation output spectrum by operating on the signal input spectrum with convolution. This method lends itself to tabular, graphical, or computer solutions, and the results can be easily interpreted. In the past the detailed calculation of intermodulation product amplitudes was a formidable task. With the techniques of this paper it should be possible to make these calculations routine. It will be feasible to determine RFI compatibility of new frequency allocations ahead of time, analyze existing RFI problems, and design receivers to work in severe interference environments. Equations are derived for the total intermodulation at a specific frequency, and for the spectrum of each order of intermodulation due to either CW or quasi-continuous input spectra. Examples are given of cross modulation, intermodulation, distortion, and third-order products.     

Field distributions in semiconductor junction circulator

The axial magnetic field distribution within a three-port semiconductor junction circulator at several frequencies is computed, and the similarity to previously published results for the axial electric field in a ferrite junction circulator illustrates the gyrotropic duality between the semiconductor and the ferrite     

Bulk carrier lifetime measurement from transient diffusion photocurrent in semiconductor diodes

The theoretical analysis of the transient diffusion photocurrent i_D(t) created in the diode substrate, following weak carrier injection level by a homogeneous photoexcitation of short duration T, shows that the decay i_D(t) can be used in two ways to obtain the substrate bulk carrier lifetime τ_ν. Depending both on the decay times t considered and the values of the substrate parameters τ_ν, D (minority carrier diffusion constant), W (thickness), s (back contact carrier recombination velocity), β (carrier velocity ratio at the p?n junction boundary), then either (1)τ_ν may be deduced from the i_D(t) decay time constant τ if τ is measured at long enough times t>t₁, or else (2)τ_ν is given by the $\text{i}{}_{\mathrm{<mtext>D</mtext>}}\text{(t)×}\text{t}$ product decay time constant θ if θ measured at short enough times t.The numerical illustration of the accuracy and validity conditions of each of the above two ways of exploiting the decay of i_D(t) is given in the case of a P type silicon substrate with a resistivity of 0.2, 1 or 10 Ω cm, W from 50 to 500 μm, τ_ν from less than 0.1 μs to more than 100 μs and various pairs of s (0 or ∞) and β (0 to ∞) values.In practice, the use of a transient photocurrent decay to obtain the diode substrate carrier lifetime also implies a previous analysis of factors such as the device response time constant and transient bias modulation, and the carrier photoexcitation level in the substrate.Experimental results obtained with N⁺P silicon-cells (W = 460 μm and 200 μm) are given and discussed as an illustration of the above study.     

Steady-state junction temperatures of semiconductor chips

The temperature drop between a transistor junction and the base of a silicon chip is dependent upon the power to be dissipated as well as the geometry of the device. This problem in three-dimensional heat conduction is analytically solved for boundary conditions which approximate a set of operating conditions. Nondimensional curves and examples summarizing typical solutions have been included to illustrate problem solving techniques.     

N 型背接触晶硅太阳电池前表面场研究

利用 Silvaco 公司的 Athena 工艺仿真软件和 Atlas 器件仿真软件,对 N 型插指背结背接触(InterdigitatedBack Contact,IBC)晶硅太阳电池普遍采用的前表面场（FSF）结构进行研究,详细分析了 IBC 晶硅电池 FSF 表面掺杂浓度及扩散深度对电池性能的影响。结果表明：具有不同表面掺杂浓度和扩散深度的 FSF 对 IBC 晶硅太阳电池短路电流密度(Jsc)、开路电压(Voc)和填充因子(FF)产生显著影响,从而影响电池的转换效率(Eff)。具有较低表面浓度、深扩散 FSF 结构的 IBC 晶硅太阳电池可获得较高转换效率,当表面掺杂浓度为 5×1017cm–3时,电池转换效率Eff最高,且随 FSF 扩散深度增加略有增加,最高转换效率可达 22.3%。     

利用半导体pn结结电容构成的沟道式电容器

为满足对电子系统中元器件性能提升、面积减小、成本降低等需求,利用感应耦合等离子体刻蚀技术(ICP),对低阻p型硅采用刻蚀、扩散、磁控溅射Al电极等工艺,使之形成凹槽状三维结构,制造出一种特殊的具有高密度电容量的硅基电容器。其特点是结构简单,电容量大(电容密度可达2.2×10–9F/mm2),容值可调,与现有微电子工艺兼容,可用于200MHz至数GHz的退耦或其他场合。同时由于半导体pn结固有的特性,该电容器可取代传统的贴片电容广泛用于电子系统中的退耦、滤波、匹配、静电和电涌防护等场合。     

The impact on power semiconductor device operation due to local electric field alterations in the planar junction termination

In this paper, we present and discuss simulation and experimental results obtained from investigating the impact of local alterations of the electric field profile in the power device planar junction termination region. Such local modifications are due to possible various extrinsic causes (manufacturing, operational or environmental) and are shown to have a critical influence on the device voltage blocking capability and reliability. The results point towards junction termination sensitivity to locally modified fields especially under voltage switching conditions due to higher leakage current densities in the modified area compared to the rest of the JT region.     

Differential photocurrent method for measurement of the optical-absorption coefficient and the minority-carrier diffusion length in a semiconductor

A new method, named DPC (differential-photocurrent), is proposed for measuring the optical-absorption coefficient and the minority-carrier diffusion length in a semiconductor. In the DPC method, a sample photodiode under a reverse bias, which is modulated at a frequency f2, is illuminated by an incident light chopped at a frequency f1, where f1and f2are close, and the DPC of the diode is measured. The method is free from limitations due to effects of surface recombination, surface reflectivity, and photon-transmission coefficient of surface layer. The optical-absorption coefficient for an n-type     

背表面场结构参数对双面太阳电池电流特性的影响

针对正面光照、背面光照及双面光照三种不同光照条件,利用TCAD半导体器件仿真软件全面系统地分析了背表面场结构参数对P型双面单晶硅太阳电池内量子效率(IQE)和短路电流密度(JSC)的影响。仿真结果表明:在300~700 nm短波段范围,双面光照情况下的IQE主要由BSF结构对背面光照光生载流子的影响决定。在700~1200 nm长波段范围,双面光照情况下的IQE主要由BSF结构对正面光照光生载流子的影响决定。当BSF扩散深度一定时,随着BSF表面浓度的增大,双面光照情况下JSC的变化特点与背面光照情况一致。BSF结构的变化对正面光照情况下JSC的影响较小((35)JSC=0.26×10~(–3)A/cm~2),而BSF结构参数的变化对背面光照情况下JSC的影响较大((35)JSC=10.59×10~(–3)A/cm~2),BSF结构对背面光照光生载流子的影响是导致双面光照JSC出现大幅变化的主要因素。     

Analysis of efficiency limitations in high-low emitter back surface field silicon solar cells

Analytical and numerical models have been used to analyse the electrical behaviour of HLE-BSF n+-n-p-p+ silicon solar cells. It is shown that this structure should have lower open-circuit voltage values than the simple HLE solar cell due to the recombination current in the p+ region. Back surface passivation is proposed as a means to improve the Voc, that can be as high as 650 mV.     

An optimized rapid aluminum back surface field technique forsilicon solar cells

Screen-printing and rapid thermal annealing have been combined to achieve an aluminum-alloyed back surface field (Al-BSF) that lowers the effective back surface recombination velocity (S_eff) to approximately 200 cm/s for solar cells formed on 2.3 Ω-cm Si. Analysis and characterization of the BSF structures show that this formation process satisfies the two main requirements for achieving low S_eff: (1) deep p⁺ regions and (2) uniform junctions. Screen-printing is ideally suited for fast deposition of thick Al films which, upon alloying, result in deep BSF regions. Use of a rapid alloying treatment is shown to significantly improve the BSF junction uniformity and reduce S_eff. The Al-BSFs formed by screen-printing and rapid alloying have been integrated into both laboratory and industrial-type fabrication sequences to achieve solar cell efficiencies in excess of 19.0 and 17.0%, respectively, on planar 2.3 Ω-cm float zone Si. For both process sequences, these cell efficiencies are 1-2% (absolute) higher than analogous cells made with unoptimized Al-BSFs or highly recombinative rear surfaces     

Electric field effect on weak localization in a semiconductor quantum wire

The influence of an electric field on weak localization in a semiconductor quantum wire is studied by a recently proposed generalized quantum Langevin equation approach to the conductivity problem. A new physical picture is presented. In our model the electronic motion is essentially one-dimensional, and the phase coherence length ℓ_φ is much larger than the elastic mean free path ℓ₂ of electrons. We find that when the electric field E exceeds a critical value E_c = KV_F/eℓ_φ, where V_F is the Fermi velocity, it will introduce a new cut-off length with implications for the experimental results on semiconductor quantum wires. Our theory is in good agreement with the experiments of Hiramoto and co-workers.     

Characterisation of charge carrier transport in thin organic semiconductor layers by time-of-flight photocurrent measurements

The paper reviews recent advances in characterisation of charge carrier transport in organic semiconductor layers by time-of-flight photocurrent measurements, with the emphasis on the measurements of the samples with co-planar electrodes. These samples comprised an organic semiconductor layer whose thickness is on the order of a μm or less, and thus mimic the structures of organic thin film transistors. In the review we emphasise the importance of considering spatial variation of electric field in these, essentially two-dimensional structures, in interpretation of photocurrent transients. We review the experimental details of this type of measurements and give examples that demonstrate exceptional sensitivity of the method to minute concentration of electrically active defects in the organic semiconductors as well as the capability of probing charge transport along the channels of different mobility that reside in the same sample.     

背表面形貌对硅太阳电池效率的影响

Different processes are used on the back surface of silicon wafers to form cells falling into three groups：textured, planar, and sawed-off pyramid back surface.The characteristic parameters of the cells, ISC, VOC, FF, Pm, and Eff, are measured.All these parameters of the planar back surface cells are the best.The FF, Pm, and Eff of sawed-off pyramid back surface cells are superior to textured back surface cells, although ISC and VOC are lower.The parasitic resistance is analyzed to explain the higher FF of the sawed-off pyramid back surface cells.The cross-section scanning electron microscopy（SEM） pictures show the uniformity of the aluminum-silicon alloy, which has an important effect on the back surface recombination velocity and the ohmic contact.The measured value of the aluminum back surface field thickness in the SEM picture is in good agreement with the theoretical value deduced from the Al-Si phase diagram.It is shown in an external quantum efficiency（EQE） diagram that the planar back surface has the best response to a wavelength between 440 and 1000 nm and the sawed-off back surface has a better long wavelength response.