Dislocation-limited minority-carrier lifetime in n-type GaP

Minority hole lifetimes as high as 2.5 ?s have been reproducibly obtained in epitaxial GaP layers grown by an isothermal liquid-phase technique. In this material, the measured lifetimes are shown to be controlled by the dislocation density ?D in the samples when ?D > 5 × 104 cm?2. A theory is presented which shows that, when the lifetime is dislocation limited, its value is close to a minimum possible value for recombination at the dislocation cores.     

Majority- and minority-carrier lifetime in MOS structures

The technique proposed by Goetzberger and Nicollian to determine carrier lifetime in MOS structures from admittance measurements in inversion, is reexamined. The interpretation of the experimental results is carried out in terms of a simplified equivalent circuit, which is topologically the same as that used by the preceding Authors, but differs for the expressions of some parameters appearing in it. The validity of the above equivalent circuit in inversion is demonstrated by comparing the frequency dependence of its admittance, both with the transmission line model, and with experimental results.

Majority and minority carrier lifetime measurements are performed on n-type 100 and 111 oriented samples, oxidized both in the presence and in the absence of hydrochloric acid. It is shown that the addition of HCl to the oxygen-gas stream has determined a three-fold increase in the majority-carrier lifetime, and a sixty-fold one in the minority-carrier lifetime. The latter observation would indicate that HCl acts on the SRH centers by modifying their capture-cross section, rather than rendering them electrically inactive as assumed in earlier papers.     

Direct observation of changes in the effective minority-carrier lifetime of SiNx-passivated n-type crystalline-silicon substrates caused by potential-induced degradation and recovery tests

We directly observed reductions in the effective minority-carrier lifetime (τ_eff) of n-type crystalline silicon (c-Si) substrates with silicon-nitride passivation films caused by potential-induced degradation (PID). We prepared PID-test samples by encapsulating the passivated substrates with standard photovoltaic-module encapsulation materials. After PID tests applying − 1000 V to the c-Si samples from the glass surface, the τ_eff was decreased, which probably pertains to Na introduced into the c-Si. After PID tests applying + 1000 V, the sample, on the other hand, showed a considerably rapid τ_eff reduction, probably associated with the surface polarization effect. We also performed recovery tests of predegraded samples, by applying a bias opposite to that used in a degradation test. The τ_eff of a sample predegraded by applying + 1000 V was rapidly completely recovered by applying − 1000 V, while those of predegraded by applying − 1000 V show only slight and insufficient τ_eff recovery.     

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.     

Microwave transmission method for measuring minority-carrier lifetime in silicon slices

A microstrip transmission method is described for measuring minority-carrier lifetime in thin silicon slices. This method is used to correct results published earlier by Makios and Thomas, using the HP 8410 network analyser as a microwave interferometer. Measured results for high-resistivity samples are shown to extend the earlier curves of Ross and Madigan.     

A fast extrapolation technique for measuring minority-carrier generation lifetime

The transient response of a pulsed MOS capacitor is used to calculate the minority-carrier generation lifetime. For Si substrate with a long lifetime, traditional approaches suffer from the inefficiency of long measurement times. An extrapolation technique presented here significantly reduces the measurement time while still maintaining good accuracy. This method applies to capacitors with constant bulk-generation rates. The linear correlation coefficient of the 1n W-t plot is monitored to ensure accuracy of the measurement technique.     

Measurement of the minority-carrier lifetime using an MOS capacitor

A simple technique is described for the measurement of the minority-carrier recombination lifetime using an MOS capacitor operating as a charge injection device. Device lag resulting from the incompleteness of the charge injection process is measured as a function of the injection pulse width. An approximate diffusion model consisting of only one adjustable parameter, the recombination lifetime, is able to explain the observed lag data. The values of the recombination lifetime thus obtained are in good agreement with those measured by photoconductive decay for a variety of Si samples. This technique permits a more definitive measurement of the minority-carder lifetime in fabricated devices than presently used procedures, without requiring high-quality devices. This technique should be particularly useful for evaluating III-V and II-VI compound semiconductors because MOS capacitors with a low density of interface states often are not available.     

Self-consistent model of minority-carrier lifetime, diffusionlength, and mobility

A self-consistent approach is proposed for extracting the minority-carrier mobility from fits to experimental data for lifetime and diffusion length and then comparing the extracted mobility to experimental mobility data. A value for electron and hole lifetime is extracted using a doping-dependent Shockley-Read-Hall mechanism with an Auger process. The hole lifetime is used to extract a minority carrier hole mobility that is consistent with the reported measurements of the hole diffusion length. The good agreement between extracted and experimental mobilities justifies incorporating the results into numerical device and circuit CAD tools     

Measurement of minority-carrier lifetime in silicon at microwave frequencies using microstrip techniques

A method is described for measuring minority-carrier lifetime in semiconductor samples of any thicknes and dimensions (e.g. silicon is used in device fabrication). The semiconductor sample is used as the dielectric of a microstrip line sandwitched between a ground plane of electroplated gold (or other metal) and electroplateted strip conductor delineated using standard photoresist masking techniques.     

Temperature-dependent minority-carrier lifetime measurements of red AlGaAs light emitting diodes

Electroluminescent decay and internal quantum efficiency measurements are made as a function of temperature on two double heterostructure AIGaAs light emitting diodes (LEDs) that emit in the visible (red) portion of the spectrum. The electroluminescent lifetimes increase by more than a factor of ten and the internal quantum efficiency falls by a factor of three as the temperature is raised from 90 to 400K. By analyzing the data with a model that accounts for the transfer with increasing temperature of the minority-carrier electrons from the direct-gap to the indirect-gap minima in the p-type active layer of these near-crossover LEDs, values for the radiative and nonradiative lifetimes as a function of temperature are obtained. A fit to the radiative-lifetime data results in an estimate of 1.3 × 10⁻¹⁰ cm³s⁻¹ for the room-temperature radiative recombination coefficient of Al_0.39Ga_0.61As, which is very similar to values reported for GaAs. The nonradiative lifetimes are found to be nearly independent of temperature from 220 to 400K and provide upper limits of 940 and 1250 cms⁻¹ for the interface recombination velocities of the two samples. These values are roughly an order of magnitude lower than any previously reported values for high-Al-content (x > 0.3) Al_xGa_1−xAs heterostructures.     

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.     

Determination of the minority-carrier lifetime in silicon ingots by photoconductivity relaxation measured at microwave frequencies

A new method for determining the bulk lifetime of minority carriers in single-crystal silicon ingots is proposed. A photoconductivity signal measured at a microwave frequency and normalized to its initial value is compared with the results of calculating the total number of excess charge carriers N(t)/N_st, where N_st corresponds to the quasi-steady-state photoconductance. The location of the point of intersection of the photoconductivity-relaxation curve and the dependence N(t=τ)/N_st determines the bulk lifetime τ=τ_v. The measurements were performed on silicon ingots with different resistivities grown by crucibleless zone melting and the Czochralski method. The experimental data obtained agree well with the results of calculation.     

Simultaneous determination of minority-carrier lifetime and deep doping profile using a double-sweep MOS-C technique

A double-sweepCVtechnology is introduced to determine the minority-carrier generation rates and the doping concentrations for non-uniform doping profile devices. The measurement time is typically less than 1 min. The observed minority-carrier lifetime decreased by one decade due to a boron implant. The Zerbst method leads to erroneous minority-carrier generation rate if a doping gradient exists in the deep-depletion region. Such error can be corrected by considering a doping concentration factor in the original Zerbst plot.     

Determination of the minority-carrier base lifetime of junction transistors by measurements of basewidth-modulation conductances

A method for determining the minority-carrier lifetime in the base of a bipolar transistor is described that involves measurement of the low-frequency, small-signal output conductance Goand reverse transconductance Gr, which arise from basewidth modulation. It involves also determining the base transit time either from calculations based on the base doping profile or from measurements at the transistor terminals. To illustrate the method, it is applied to transistors having considerably different base lifetimes.     

Measurement of minority carrier lifetime in n-type MBE HgCdTe and its dependence on annealing

Results are presented for minority carrier lifetime in n-type molecular beam epitaxy Hg_1−xCd_xTe with x ranging from 0.2 to 0.6. It was found that the lifetime was unintentionally degraded by post-growth annealing under Hg saturated conditions in a H₂ atmosphere that was both time and temperature dependent. This effect was minimal or non-existent for x∼0.2 material, but very strong for x ≥ 0.3. Hydrogen was identified as responsible for this degradation. Identical annealing in a He atmosphere avoids this degradation and results in neartheoretical lifetime values for carrier concentrations as low 1 × 10¹⁵ cm⁻³ in ≥0.3 material. Modeling was carried out for x∼0.2 and x∼0.4 material that shows the extent to which lifetime is reduced by Shockley-Real-Hall recombination for carrier concentrations below 1 × 10¹⁵ cm⁻³, as well as for layers annealed in H₂. It appears that annealing in H₂ results in a deep recombination center in wider bandgap HgCdTe that lowers the lifetime without affecting the majority carrier concentration and mobility.     

Minority carrier lifetime in doped and undoped epitaxially grown n-type CdxHg1−xTe

The performance of infrared detectors made from Cd_xHg_1-xTe (CMT) is related to the lifetime of minority carriers in the material. Both photoconductive and photovoltaic devices require long lifetimes for high performance. This paper compares lifetime measurements on epitaxially grown CMT layers which have been isothermally annealed to minimize the vacancy concentration and are n-type due to native defects, residual impurities, or deliberately added dopants. Layers grown by liquid phase epitaxy (LPE), metalorganic vapor phase epitaxy (MOVPE), and molecular beam epitaxy (MBE) have been considered, in all cases the same measurement system was used under the same low injection conditions. All layers were of compositions required for operation in the 8 to 14 μm wavelength range. Comparisons have been made between undoped and indium doped LPE layers and undoped and iodine doped MOVPE layers. It was hoped that a deliberately introduced donor impurity would give better control of the n-type properties. The effect of passivation on the measurement of lifetime has also been considered, the results showing that a surface with a native oxide is required to obtain the true bulk lifetime as has been seen previously for bulk material.     

Modeling and measurement of minority-carrier lifetime versus doping in diffused layers of n+-p silicon diodes

The results of minority-carrier lifetime measurements in heavily phosphorus-doped n⁺diffused layers of p-n junction diodes using a spectral response technique are reported in this paper. Exact modeling of current-flow equations, modified to include bandgap reduction due to high carrier concentration and Auger recombination, is used to compute the dependence of diffused-layer photocurrent Jpthon the incident light energy and intensity. The photocurrent in the diffused layer is also obtained by subtracting the theoretical value of the space charge and uniformly doped p-region component from the experimentally measured photocurrent of the diode at each wavelength. Note that all calculated values based on light intensity include computed transmittance/reflectance through the oxide layer at each wavelength. The comparison of the values of Jpthwith Jpexp, using nonlinear least square techniques, then directly gives the lifetime profile in the diffused layer. A simple expression is given for lifetime as a function of doping which may be used in modeling and prediction of device performance. Using this experimental technique it was found that the lifetime in the diffused layer is an order of magnitude less than that corresponding to uniformly doped bulk-silicon values and is very much process dependent; its value being 3.72 × 10^-11s for surface concentration of 3.0 × 10²⁰cm^-3and increases to 2.9 × 10^-8s at doping concentration of 1.0 × 10¹⁷cm^-3.     

Dynamic minority-carrier storage in TRAPATT diodes

The occurrence of a dynamic storage of minority carriers in the highly-doped boundary regions of a TRAPATT diode and the subsequent release of these carriers into the diode's depletion region is verified for the first time in detailed computer simulations of the diode's internal dynamics. The simulations were carried out by numerical solution of the carrier transport equations in a p⁺?n?n⁺ silicon diode having a deep-diffused doping profile typical of experimental devices. The results show that it is this storage process, and not thermal generation, that controls the carrier avalanche even in very gradually graded structures. The dynamics of this phenomenon are described in detail and the implications of the results on TRAPATT oscillator performance are discussed.