Minority-carrier transport parameters in degenerate n-type silicon

Direct measurements of the minority-hole transport parameters in degenerate n-type silicon were done by analyzing transient photocurrent in the frequency domain. Minority-hole mobility is found to increase with doping for dopings larger than 4×10¹⁹ cm^-3 . The ratio of minority-hole to majority-hole mobility is found to be about 2.8 at N_D=7.2×10¹⁹ cm^-3. The measured lifetime shows a strongly Auger-dependent mechanism. The extracted Auger coefficient at 296 K is C_n =2.22×10^-31 cm⁶-s^-1, and is in agreement with that reported on other works. Self-consistent checking is used to validate the accuracy of the measured results     

Measurement of steady-state minority-carrier transport parameters in heavily doped n-type silicon

The relevant hole transport and recombination parameters in heavily doped n-type silicon under steady state are the hole diffusion length and the product of the hole diffusion coefficient times the hole equilibrium concentration. These parameters have measured in phosphorus-doped silicon grown by epitaxy throughout nearly two orders of magnitude of doping level. Both parameters are found to be strong functions of donor concentration. The equilibrium hole concentration can be deduced from the measurements. A rigid shrinkage of the forbidden gap appears as the dominant heavy doping mechanism in phosphorus-doped silicon.     

Minority-carrier diffusion coefficients and mobilities in silicon

A new method for accurate measurement of minority-carrier diffusion coefficients in silicon is described. The method is based on a direct measurement of the minority-carrier transit time through a narrow region of the p-n junction diode. The minority-carrier mobility is obtained from the diffusion coefficient using the Einstein relation. The method is demonstrated on low-doped n- and -p-type Si (dopings ∼10¹⁵cm^-3) and is compared with the literature data for the majority-carrier mobilities. The results show that in low-doped Si the electron minority- and -majority-carrier mobilities are comparable, but the hole minority-carrier mobility is significantly higher (∼30 percent) than the corresponding majority-carrier value. The results confirm earlier data of Dziewior and Silber.     

Minority-carrier transport parameters in heavily doped p-typesilicon at 296 and 77 K

Minority-carrier electron lifetime, mobility and diffusion length in heavily doped p-type Si were measured at 296 and 77 K. It was found that a 296 K μ_n (pSi)≈μ_n (nSi) for N _AA≲5×10¹⁸ cm^-3, while μ_n (pSi)/μ_n (nSi)≈1 to 2.7 for higher dopings. The results also show that for N_AA≲3×10¹⁹ cm^-3, D (pSi) at 77 K is smaller than that at 296 K, while for higher dopings D_n (pSi) is larger at 77 K than at 296 K. μ_n (pSi) at 77 K increases with the increasing doping above N_AA>3×10¹⁸ cm^-3, in contrast to the opposite dependence for μ_n (nSi) in n⁺ Si     

Novel method for extraction of hole transport parameters in heavily doped n-type emitter

A novel method is reported for the extraction of the hole transport parameters from the emitter of an n/sup +/pn bipolar transistor. The parameters are decoupled with a reliable algorithm based on the numerical solution of the transport equations. Accurate modelling of the optical spectral response of the base current has been achieved.<>     

Minority-carrier lifetime analysis of silicon epitaxy and bulkcrystals with nonuniformly distributed defects

Existing analyses of the pulsed response of an MOS capacitor for minority-carrier lifetime determination result in a lifetime value averaged over most of the depletion region width. The authors present an analysis of MOS capacitance-versus-time data that enables minority-carrier generation lifetime to be plotted as function of depletion-region depth. The technique is shown to be useful for samples with bulk or buried interfacial layer defects that have defect-free surfaces. Data are presented for intrinsically gettered bulk crystals and extrinsically gettered Si (2%Ge) epitaxial layers with misfit dislocations. For samples that do have uniform lifetimes, the measurement time required for determining carrier lifetime is reduced by more than an order of magnitude     

Minority-carrier lifetime in dielectrically isolated single-crystal silicon films defined by electrochemical etching

The minority-carrier lifetime has been measured in thin, dielectrically isolated single-crystal silicon films defined by electrochemical etching. Both transient-current measurements on deep-depletion MOS transistors and recombination-current measurements on bipolar junction transistors have been use to determine the lifetime. Values of the order of 1 μ sec have been observed in both n-and p-type films with dopant concentrations of about 10¹⁵ cm^?3. It was found that the characteristics of the MOS transistors were not dominated by generation at either surface of the thin film. No differences were seen between the characteristics of bipolar transistors fabricated in the thin films and those of transistors fabricated in bulk control wafers.     

Measurement of the minority-carrier transport parameters in heavily doped silicon

A new method for simultaneous measurement of bandgap narrowing and diffusion length in a heavily doped n⁺substrate is proposed. The method uses planar test pattern at the front side of the substrate to determine the hole minority-carrier current injected from a p-type emitter and diodes at the rear side to measure diffusion lengths. The method can be generalized such that the minority-carrier diffusion constant can be estimated and the use of extrapolated literature data can be avoided. Results of measured values of bandgap narrowing and diffusion length versus impurity concentration are given for n-type material.     

High-temperature carrier transport in n-type epitaxial GaAs

Resistivity and Hall coefficient have been measured in the temperature range 300-1250 K on samples of n-type epitaxial GaAs from which the substrates have been removed to eliminate substrate conduction at high temperatures. These data are useful for determining energy band parameters as well as for modeling epitaxial growth and other high temperature phenomena. The mobilities of electrons in the Γ₆^c minimum and L₆^c minima and the mobility of holes in the Γ₈^v maxima were calculated for the temperature range 300-970 K. From these calculations the mobility in the L₆^c minima was found to decrease faster with increasing temperature than the mobility in the Γ₆^c minimum. Using the temperature dependence of the mobilities, the Γ₆^c ? L₆^c ? X₆^c ordering of the conduction band minima, and a calculated intrinsic carrier concentration, a self-consistent model for four-band carrier transport was obtained.     

Defect analysis of n-type silicon strained layers

The structural and electrical properties of n-type silicon strained layers, sandwiched between Si_1−xGe_x layers, with x=0.15, 0.20 and 0.30 have been investigated using a combination of analytical techniques. Here, the focus is on the application of deep level transient spectroscopy (DLTS) on p–n junction structures, to assess non-radiative generation-recombination centres. It will be demonstrated that successful analysis can only be applied if the edges of the devices are chemically passivated. Finally, it is shown that for low-leakage diodes, the quantum-well properties can, in principle, be extracted from the combined DLTS and capacitance–voltage/capacitance–temperature characteristics.     

Nano-photonic crystal formation on highly-doped n-type silicon

We present a novel electrochemical technique for the fabrication of nano-photonic crystal structures. Based on a specially designed electrolyte, porous silicon(PSi) layers with different porosities are possible to be produced on highly-doped n-type silicon substrate by varying the applied current density which determines the size and the morphology of pores. By applying an alternative current density modulation during anodization, porous silicon photonic crystals are obtained using HF-containing electrolyte without oxidizing components. The current burst model(CBM) is employed to interpret the mechanism of the formation of the macropore porous silicon.     

Measurement of hole mobility in heavily doped n-type silicon

Accurate measurements of the mobility (and diffusion coefficient) of minority-carrier holes in Si:P with doping in the 10¹⁹cm^-3range have been done. The technique employed the measurement of diffusion length by means of lateral bipolar transistors of varied base widths, and the measurement of minority-carrier lifetime on the same wafers from the time decay of luminescence radiation after excitation with a short laser pulse. Minority-carrier hole mobility is found to be about a factor of two higher than the mobility of holes as majority carriers in p-type Si of identical doping levels.     

Disordered wall arrays by photo-assisted electrochemical etching in n-type silicon

The fabrication of ordered, high aspect-ratio microstructures in silicon by use of photo-assisted electrochemical etching is an important technology, where voltage and current density are significant factors. In this paper, disordered walls appear in 5-inch n-type silicon wafers when a large current density is used. Based on the theory of space charge region, these disordered walls are caused by the contradiction between the protection from dissolution by a high applied voltage and the dissolution by a high current density. To verify this point, wall arrays were fabricated at different applied voltages and current densities. Moreover, the critical voltage was kept constant and different current densities were applied to obtain conditions for avoiding disordered walls and achieving uniform wall arrays. Finally, a wall array with a period of 5.6μm and a depth of 55μm was achieved at an applied voltage of 3 V and a monotonically increasing current density ranging from 22.9 to 24.5 mA/cm².     

Minority-carrier lifetime measurements on silicon solar cells using Iscand Voctransient decay

Measurements of the transient decay of short-circuit current and open-circuit voltage of solar cells provide sufficient information, in principle, to determine both the effective back-surface recombination velocity S and the base minority-carrier lifetime τ. The practical use of the method is illustrated by an example, and the technique is applied to a variety of cells. Analysis of the effect of different cell thickness on the measurement is included. Finally, some limitations, both fundamental and experimental, are discussed.     

Carrier transport in porous silicon

Carrier transport in porous silicon layers has been studied by the time-of-flight method in the strong injection mode at temperatures T=290–350 K and electric field strengths F=(1.5–7)×10⁴ V cm^?1. The electron and hole drift mobilities μ_e≈2×10^?3 cm² V^?1 s^?1 and μ_h≈6×10^?4 cm² V^?1 s^?1 were obtained at T=292 K and F=4×10⁴ V cm^?1. An exponential temperature dependence of drift mobility with activation energy of ～0.38 and ～0.41 eV for, respectively, electrons and holes was established. It is shown that the type of time dependences of the photocurrent associated with carrier drift and the superlinear dependence of the transit time on the reciprocal of the voltage applied to a sample allow use of the concept of space-charge-limited currents under the conditions of anomalous dispersive transport. The experimental data are accounted for in terms of the model of transport controlled by carrier trapping into localized states with energy distribution near the conduction and valence band edges described by an exponential function with a characteristic energy of ～0.03 eV.     

Cu掺杂n型硅材料的制备及热敏特性研究

通过高温扩散的方法制备出铜掺杂的n型单晶硅材料,详细研究了不同制备条件所得材料的电学及热敏特性。结果表明当铜表面源浓度为1.83×10-7mol/cm2时,1200℃下扩散2个小时得到的铜掺杂补偿硅材料的电阻率达到最大值46.2Ω?cm。测试表明铜掺杂n型单晶硅材料具有良好的负温度系数热敏特性,B值分布于3010K-4130K之间。     

Performance of bifacial HIT solar cells on n-type silicon substrates

The performance of amorphous silicon(a-Si:H) /crystalline silicon(c-Si) heterojunction is studied,and the effects of the emitter layer thickness,doping concentration,intrinsic layer thickness,back heavily-doped n layer,interface state and band offset on the optical and electrical performance of bifacial heterojunction with intrinsic thin-layer(HIT) solar cells on ntype silicon substrates are discussed.It is found that the HIT solar cells on n-type substrates can obtain a higher conversion efficiency than th...     

Minority-carrier injection into polysilicon emitters

The hole transport equation is solved for a polysilicon emitter of a bipolar transistor. The recombination at the grain boundaries as well as at the poly-monosilicon interface is considered. An effective surface recombination velocity is defined and calculated as a function of surface state density and number of grain boundaries. A comparison between the injected hole current into the diffused region of both an Al contact and a polysilicon-silicon emitter is given as a function of surface state density for different numbers of grain boundaries. Also the injected current is calculated for different values of junction depth and surface concentration.     

High-temperature spreading-resistance profiling for the characterization of impurity distributions in n-type silicon

We have developed the technique of high-temperature spreading-resistance profiling (HT-SRP) for the characterization of electrically active impurities or defects in semiconductors. As a major feature, HT-SRP together with the well-established SRP method at room temperature combines the accurate resolution of an impurity profile with a determination of the defect states that control the electronic properties of the semiconductor. Some basic aspects of this technique are demonstrated on Si samples diffused with sulfur or selenium.     

Multistage performance deterioration in n-type crystalline silicon photovoltaic modules undergoing potential-induced degradation

This study addresses the behavior of n-type front-emitter (FE) crystalline-silicon (c-Si) photovoltaic (PV) modules in potential-induced degradation (PID) tests with a long duration of up to 20 days. By PID tests where a negative bias of −1000 V was applied at 85 °C to 20 × 20-mm²-sized n-type FE c-Si PV cells in modules, the short-circuit current density (J_sc) and the open-circuit voltage (V_oc) started to be decreased within 10 s, and strongly saturates within approximately 120 s, resulting in a reduction in the maximum output power (P_max) and its saturation. After the saturation, all the parameters were almost unchanged until after 1 h. However, the fill factor (FF) then started to decrease and saturated again. After approximately 48 h, FF further decreased again, accompanied by a reduction in V_oc. The first degradation is known to be due to an increase in the surface recombination of minority carriers by the accumulation of additional positive charges in the front Si nitride (SiN_x) films. The second and third degradations may be due to significant increases in recombination in the space charge region. The enhancement in recombination in the space charge region may be due to additional defect levels of sodium (Na) introduced into the space charge region in the p–n junction. We also performed recovery tests by applying a positive bias of +1000 V. The module with the first degradation completely recovered its performance losses, and the module with the second degradation was almost completely recovered. On the contrary, the modules with the third degradation could not be recovered. These findings may improve the understanding of the reliability of n-type FE c-Si PV modules in large-scale PV systems.