Lifetime In Silicon Research Articles

Effect of RPT/furnace processing on the minority carrier lifetime in very thin oxide MOS capacitors

In this paper the effects of oxidation and annealing processes on the minority carrier lifetime in silicon have been investigated. Using the pulsed MOS capacitor method a comparison of two methods used to grow very thin SiO 2 layers, conventional furnace processing and rapid thermal processing (RPT), has been carried out. It is shown that those substrates which underwent RT high temperature steps sustained less damage, probably due to the lower contamination that results from this method.

A simple procedure based on the PCD method for determination of recombination lifetime and surface recombination velocity in silicon

A two-step method based on measurement of the decay of photoconductivity and use of chemical surface passivation has been developed to determine both recombination lifetime and surface recombination velocity of carriers in high-resistivity silicon. Lifetime up to 3-4 ms and surface recombination velocity down to 2-5 cm s-1 can be measured on samples no more than 300 mu m thick. The method can be used in a wide field of applications, especially for material characterization and process control.

Metals, Oxide Precipitates and Minority Carrier Lifetime in Silicon

Metals, Oxide Precipitates and Minority Carrier Lifetime in Silicon

Effect of ultraviolet irradiation upon the recombination lifetime of silicon wafers covered with a dielectric film

The effect of UV irradiation upon the recombination lifetime of silicon covered with chemical vapor deposition (CVD) oxide has been studied using a laser-microwave photoconductance (LM-PC) technique. It is found that the lifetime changes little after the first UV irradiation, but dramatically decreases following thermal annealing at 500 K for 1 h. Moreover, the lifetime can be cycled up and down by repeated irradiation and thermal annealing. A comparison is made of the UV irradiation effect upon the lifetime of silicon wafers covered with a variety of different dielectric films. It is suggested that UV rechargeable defects are present in a CVD oxide film, like in native oxide and CVD nitride, but are absent in thermal oxide. Finally, it is emphasized that the noncontact LM-PC technique can be a powerful tool to characterize the defects in dielectric films on silicon wafers.

Plasma-enhanced chemical-vapor-deposited oxide for low surface recombination velocity and high effective lifetime in silicon

It is shown that plasma-enhanced chemical-vapor deposition (PECVD) of thin SiO2 on Si wafers followed by rapid thermal annealing (RTA) can result in very high effective carrier lifetime (≳5 ms) and extremely low surface recombination velocity (≤2 cm/s). Thin SiO2 (∼100 Å) layers were prepared by direct PECVD at 250 °C and RTA was performed at 350 °C in forming gas. Detailed metal-oxide-semiconductor analysis and model calculations showed that such a low recombination velocity is the result of moderately high positive oxide charge (5×1011–1×1012 cm−2 ) and relatively low midgap interface-state density (5×1010–1×1011 cm−2 eV−1). RTA was found to be superior to furnace annealing, and a forming gas ambient was better than a nitrogen ambient for achieving a very low surface recombination velocity. Some degradation in the surface recombination velocity or effective lifetime was observed. It is found that a PECVD SiN cap on top of the thin SiO2 not only suppressed this degradation but also enhanced the effective lifetime.

Response to‘‘ Comment on ‘Temperature dependence of the radiative lifetime in porous silicon’ ’’

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Comment on ‘‘Temperature dependence of the radiative lifetime in porous silicon’’

Comment on ‘‘Temperature dependence of the radiative lifetime in porous silicon’’

A novel technique for the simultaneous measurement of ambipolar carrier lifetime and diffusion coefficient in silicon : Mats Roslinget al. Solid-State Electronics35(9), 1223 (1992)

A novel technique for the simultaneous measurement of ambipolar carrier lifetime and diffusion coefficient in silicon : Mats Roslinget al. Solid-State Electronics35(9), 1223 (1992)

Investigation of charge trapping centers in silicon nitride films with a laser-microwave photoconductive method

A new method using a laser microwave photoconductance (LMPC) technology for the investigation of charge trapping centers in silicon nitride films was demonstrated by studying the ultraviolet (UV) irradiation effect upon minority-carrier recombination lifetime of silicon with the film. The lifetime is found dependent on the film thickness. UV irradiation dramatically decreases the lifetime for the samples with the thick film. The decreased lifetime is transient and recovers to the initial value after long time storage at room temperature. The recovery accelerates with increasing temperature. The lifetime behavior is correlated with the charge states of K centers in the nitride film. It is then shown that the electronic structure of the charge trapping centers can be studied by an investigation of the lifetime recovery process after UV irradiation with temperature controlled LMPC measurements.

Temperature dependence of the radiative lifetime in porous silicon

Using photoluminescence decay measurements the radiative lifetime of porous silicon is investigated between liquid helium and room temperature. The radiative recombination mechanism in porous silicon is in essence the same as in bulk silicon, viz. a phonon mediated indirect transition. The functional dependence of the lifetime on photon energy reveals the confinement character of the recombination carriers. The high external photoluminescence efficiency is well explained by the reduction of nonradiative recombination owing to low mobility, to low dimensionality, and to the extreme low surface recombination rate, and is further enhanced by the relatively small refractive index.

A model for the field and temperature dependence of Shockley-Read-Hall lifetimes in silicon

We derive a simple analytical model for the field and temperature dependence of Shockley-Read-Hall lifetimes in silicon from a microscopic level, where the capture of carriers at recombination centers is assumed to be a multiphonon process. Strong electric fields, as often present in modern devices, cause trap assisted tunneling, i.e. the multiphonon recombination path is no longer purely vertical in a band diagram, but has a horizontal branch at an effective energy which is given by the maximum of the transition probability. Applying reasonable approximations we calculate this effective recombination path as a function of field strength and temperature. Field enhancement factors of the inverse carrier lifetimes are then presented that require no integration, iteration or higher mathematical functions. The anisotropy and multi-valley nature of the silicon conduction band is carefully taken into account. We discuss all approximations and physical effects by means of the gold acceptor level. The model is able to describe the pre-breakdown behaviour of trap tunneling leakage and is suitable for the implementation into simulation packages.

A novel technique for the simultaneous measurement of ambipolar carrier lifetime and diffusion coefficient in silicon

Using the classical semiconductor continuity equation, a new method for the simultaneous extraction of the ambipolar carrier lifetime and the ambipolar diffusion coefficient for high injection levels is developed. The method uses carrier decay measurements based on the free-carrier absorption (FCA) technique. The measurements are performed in the base of p- i- n type diodes, where the middle region is a lightly n-doped base region. By varying the forward bias, the ambipolar lifetime and diffusion coefficients are studied for different excess-carrier concentrations ranging approx. 2–4 decades above the base doping. Both the lifetime and diffusion coefficients agree well with theoretical models. The theoretical ambipolar diffusion coefficients agree well with theoretical models. The theoretical ambipolar diffusion coefficient is calculated using the values of D n and D p , which, in turn, are determined from mobility models and the Einstein relation. The mobility models used include carrier-carrier scattering effects which are important in the explanation of high-injection dependence.

Transient recovery of minority-carrier lifetime in silicon after ultraviolet irradiation

A recovery process of minority-carrier recombination lifetime after ultraviolet (UV) irradiation has been investigated with a laser-microwave photoconductance technique for silicon wafers with native oxide. It is found that the effective lifetime which greatly increases after UV irradiation recovers to the initial value primarily with an exponential law characterized by a specific time constant called recovery time. The recovery time depends on experimental conditions where, for example, an accumulation effect of UV irradiation is observed. A mechanism of the effective lifetime recovery process is correlated mainly with the behavior of slow states associated with the silicon/native oxide interface.

A study of disordered regions in neutron irradiated Si

Disordered regions produced by neutron irradiation are highly effective in degrading the minority carrier lifetime in silicon. The carrier recombination processes in silicon are analyzed, with the characteristics of the disordered regions taken into account. A self-consistent physical model for computation is then presented. The numerical results show the dependence of the minority carrier lifetime degradation on the defect state distribution, the electric potential height and the excess carrier concentration. A comparison of this model with the point defect model and experiments proves its validity.

A study of carrier lifetime in silicon by laser-induced absorption: A perpendicular geometry measurement

In this paper, we describe an innovative and improved measurement of carrier lifetime in Si when i.r. laser-induced absorption is applied in perpendicular geometry. Carrier lifetime depth-distributions can be examined in one measurement for a wide range of injection levels, 10 11–10 17 cm −3. We emphasize the capacity of distinguishing different recombination mechanisms and the determination of recombination lifetime reduction after certain sample treatment procedures. Examples of in-depth, non-homogeneous lifetime changes after wafer sawing and intrinsic gettering treatments are presented. The developed technique has important advantages in comparison with thickness-averaged carrier lifetimes obtained with conventional measurement techniques where different specific injection levels are usually imposed.

Infiuence of Static and Alternating Fields on Positron Lifetimes in Silicon and Germanium

Infiuence of Static and Alternating Fields on Positron Lifetimes in Silicon and Germanium

Radiation damage and minority carrier lifetime in crystalline silicon

The lifetime of the minority carriers in p and n type crystalline silicon was measured with 1 MeV pulsed electron beam. Silicon samples were exposed to different fluences of 1 and 6 MeV electron, 14 MeV neutrons, thermal neutrons and 60Co gamma rays and the value of the radiation damage coefficient for each sample was estimated by monitoring variations in the minority carrier lifetime with radiation fluence. It is found that 14 MeV neutrons can be effectively used in reducing the lifetime of minority carriers in silicon and therefore have potential in controlling parameters of semiconductor devices.

Temperature dependence of minority-carrier lifetime in iron-diffused p-type silicon wafers

Minority-carrier recombination lifetime was measured with a noncontact laser/microwave method for nondiffused and iron-diffused p-type silicon wafers in the temperature range from 28 °C to 230 °C. The lifetime increased monotonically with temperature in nondiffused silicon, while the lifetime in iron-diffused silicon showed a broad peak around 110 °C and a depression around 170 °C. The temperature dependence of the lifetime in iron-diffused silicon was analyzed based on Shockley–Read–Hall statistics. The origin of the lifetime temperature dependence was attributed to the dissociation of iron-boron pairs. Our experimental data supported that an electron trap for an iron-boron pair at Ec−0.29 eV was more effective as a recombination center than a hole trap at Ev + 0.1 eV. It was also shown that the effect of iron in concentrations as low as 1×1011 cm−3 on the lifetime can be detected with the noncontact laser/microwave method.

Picosecond Photocarrier Lifetimes in Ion-Irradiated Amorphous and Crystalline Silicon

ABSTRACTCrystalline silicon (c-Si) and structurally relaxed amorphous silicon (a-Si) were implanted with 1 MeV Si+ at liquid nitrogen temperature. The photocarrier lifetime τ in the implanted samples was determined with sub-picosecond resolution through pump-probe reflectivity measurements. At low damage levels (i.e. <1014 ions/cm2), τ decreases with increasing ion dose in both materials, indicating a build up of trapping and recombination centers. The dominant centers in c-Si appear to be related to simple defects. The generation rate of electrically active defects is found to be the same in relaxed a-Si and c-Si, which suggests that the structural defects formed in a-Si strongly resemble the simple defects in c-Si. For ion doses > 1014 /cm2, τ saturates at a level of 0.8 ps for both materials. Strikingly, the saturation sets in far below the dose needed to amorphize (>1015 /cm2). The defect density in a-Si at saturation is estimated to be ≈1.6 at.%.

Contactless optical evaluation of processing effects on carrier lifetime in silicon

Contactless, optical modulation of free-carrier absorption has been used to identify minority-carrier lifetime degradation associated with both novel and common very large scale integrated circuit processing steps in p-type silicon wafers. Carrier lifetime degradation and a corresponding increase in surface recombination velocity was found to be associated with the silicon etchants ethylenediamine-pyrocatechol-water (EDP) and potassium hydroxide (KOH), prolonged exposure to hydrofluoric acid (HF and BHF), and ion bombardment associated with a variety of plasma etching steps. Knowledge of process-induced lifetime degradation obtained by this technique may offer significant input into the development of high-yield very large scale integrated circuit processes.