The dominant mechanisms of charge-carrier scattering in lead telluride

The present status of the dominant mechanisms of charge-carrier scattering in lead telluride is analyzed critically. It is shown that the role of the Coulomb potential of the vacancies and the role of the deformation potential of acoustic phonons in carrier scattering in PbTe has been strongly overestimated in most existing studies. Futhermore, the role of optical phonons at high temperatures has been unjustifiably reduced to a polar component only. It is shown that, in addition to this mechanism, the deformation potential due to optical phonons, whose greatest contribution is at high carrier densities, also plays an important role in carrier scattering processes at temperatures in the range of room temperature. Fiz. Tekh. Poluprovodn. 31, 281–284 (February 1997)     

Water-enhanced negative bias temperature instability in p-type low temperature polycrystalline silicon thin film transistors

Water-enhanced degradation of p-type low temperature polycrystalline silicon thin film transistors under negative bias temperature (NBT) condition is studied. H₂O penetration into gate oxide network and the role of H₂O during NBT stress are confirmed and clarified respectively. To prevent H₂O diffusion, a combination of a layer of PECVD SiO₂ and a layer of PECVD Si₃N₄ as passivation layers are investigated, revealing that 100 nm SiO₂ and 300 nm Si₃N₄ can effectively block H₂O diffusion and improve device NBT reliability.     

Minority-charge-carrier mobility at low injection level in semiconductors

From the kinetic equations, the distribution functions for majority and minority charge carriers are obtained at a low injection level. For describing the electron-hole collisions, the Landau collision integral is used. The carrier scattering at ionized or neutral impurity and at acoustic phonons is taken into account. The majority-carrier distribution function is presented in the analytical form. The minority-carrier mobility is calculated and analyzed, and the features of its behavior at low temperatures are revealed. It follows from the developed theory that the hole mobility in an n-type material increases with doping and neutral-impurity concentration. This effect is attributed to mutual charge-carrier collisions and different effective masses of different-sign carriers.     

Calculation of the charge-carrier mobility in diamond at low temperatures

The discrepancies between the quasi-elastic and inelastic approaches to the calculation of the electron and hole mobilities in diamond at low temperatures when the carrier scattering from acoustic phonons becomes significantly inelastic have been numerically estimated. The calculations showed that the mobility described by a close-to-equilibrium distribution function differs several times from that obtained within the quasi-elastic approach even at 20 K. The results obtained are important for interpreting the low-temperature electrical experiments on high-purity diamond single crystals.     

Infrared tomography of the charge-carrier lifetime and diffusion length in semiconductor-grade silicon ingots

A nondestructive method for measuring the three-dimensional distribution of the charge-carrier lifetime and diffusion length in silicon ingots with a length of up to 1 m and a diameter as large as 0.3 m is presented. Physically, this method is based on infrared crossed-beam probing of an ingot with polished surface areas. One of the beams is repetitively pulsed, has a wavelength of 1.15–1.28 μm, and generates excess charge carriers in a rodlike zone along the beam trajectory in the ingot. Other beams are continuous and have longer wavelengths; these beams detect the temporal and spatial kinetics of excess charge carriers in a small portion of the rodlike zone and in the vicinity of it (the free-carrier absorption is measured). By virtue of the fact that the investigated zone is at a distance from the ingot surface, there is no need to consider the surface recombination. The capabilities of the method are demonstrated for an ingot with known spatial nonuniformity of the charge-carrier lifetime. Spatial resolution amounting to several millimeters was attained. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 1, 2001, pp. 40–47. Original Russian Text Copyright ? 2001 by Akhmetov, Fateev.     

Transient high level majority and minority carrier photocurrents in p-type silicon Schottky barrier diodes—II: Comparison with computer calculations

Computer calculations of majority and minority carrier transient current pulses in a totally depleted silicon diode are compared with experimental current pulse shapes obtained by light pulse excitation of the diode. Numerical solution of the transport equations permitted the roles of the field dependence of the carrier mobility and of the excitation depth of the exciting light pulse to be investigated. Improved agreement of the computer solution as compared to previously made analytical calculations, particularly under conditions of high electric field or high space charge, is found.     

Defects in annealed 1.5 MeV boron implanted p-type silicon

Effects of temperature and dosage on the evolution of extended defects during annealing of MeV ion-implanted Czochralski (CZ) p-type (001) silicon have been studied using transmission electron microcopy. Excess interstitials generated in a 1 10¹⁵ cm⁻²/1.5 MeV B⁺ implanted Si have been found to transform into extended interstitial {311} defects upon rapid thermal annealing at 800°C for 15 sec. During prolonged furnace annealing at 960°C for 1 h, some of the {311} defects grow longer at the expense of the smaller ones, and the average width of the defects seems to decrease at the same time. Formation of stable dislocation loops appears to occur only above a certain threshold annealing temperature (∼1000°C). The leakage current in diodes fabricated on 1.5 MeV B⁺ implanted wafers was found to be higher for a dosage of 1 10¹⁴cm⁻² and less, as compared to those fabricated with a dosage of 5 10¹⁴ cm⁻² and more. The difference in the observed leakage current has been attributed to the presence of dislocations in the active device region of the wafers that were implanted with the lower dosage.     

利用多孔硅层增强P型CZ硅中吸杂效率的一种新方法

A new two-step phosphorous diffusion gettering(TSPDG) process using a sacrificial porous silicon layer(PSL) is proposed.Due to a decrease in high temperature time,the TSPDG(PSL) process weakens the deterioration in performances of PSL,and increases the capability of impurity clusters to dissolve and diffuse to the gettering regions.By means of the TSPDG(PSL) process under conditions of 900℃/60 min + 700℃/30 min,the effective lifetime of minority carriers in solar-grade(SOG) Si is increased to 14.3 times ...     

Isochronal annealing study of hydrogen interaction with implantation-induced point defects in p-type silicon

Isochronal annealing with zero and reverse bias applied to Schottky diodes was used to monitor the evolution of hydrogen interaction with point defects observed in hydrogen-implanted p-type silicon, i.e., divacancy (VV), carbon–oxygen interstitial pair (C_iO_i) and two levels at E_v+0.28 and E_v+0.50 eV. The VV and C_iO_i are passivated by hydrogen liberated from hydrogen-containing defects during annealing in the temperature range 90–150°C and reappear upon annealing above 180°C under reverse bias due to hydrogen liberation and its field drift. Two levels at E_v+0.50 and E_v+0.28 eV are ascribed to irradiation-induced and hydrogen-related defects, respectively.     

Carrier mobilities in silicon semi-empirically related to temperature,doping and injection level

From a review of different publications on the carrier mobilities in silicon, the authors propose an approximated calculation procedure which permits a quick and accurate evaluation of these mobilities over a large range of temperatures, doping concentrations and injection-levels.The proposed relations are well adapted to semiconductor device simulation becuase they allow short computation times.     

A novel method to enhance the gettering efficiency in p-type Czochralski silicon by a sacrificial porous silicon layer

A new two-step phosphorous diffusion gettering(TSPDG) process using a sacrificial porous silicon layer(PSL) is proposed.Due to a decrease in high temperature time,the TSPDG(PSL) process weakens the deterioration in performances of PSL,and increases the capability of impurity clusters to dissolve and diffuse to the gettering regions.By means of the TSPDG(PSL) process under conditions of 900℃/60 min + 700℃/30 min,the effective lifetime of minority carriers in solar-grade(SOG) Si is increased to 14.3 times its original value,and the short-circuit current density of solar cells is improved from 23.5 o 28.7 mA/cm~2,and the open-circuit voltage from 0.534 to 0.596 V along with the transform efficiency from 8.1%to 11.8%,which are much superior to the results achieved by the PDG(PSL) process at 900℃for 90 min.     

A theoretical explanation of the carrier lifetime as a function of the injection level in gold-doped silicon

An expression for the recombination rate in gold-doped silicon is derived taking into account both gold energy levels. This formula shows that the dominant energy level under high-injection conditions is not the midgap gold acceptor, but the gold donor level. The high-low injection lifetime ratio calculated with the derived expression is in good agreement with measured values. This indicates that lifetime and capture cross section measurements are consistent with each other. The relation between gold concentration and high-injection lifetime is calculated. The relative density of the neutral and the negatively and positively charged traps is shown as a function of the carrier injection level.     

Classification of macroscopic defects contained in p-type EFG ribbon silicon

Recombination behavior of the grown-in defects contained in p-type ribbon silicon has been examined. Minority carrier lifetime at various defect sites was measured as a function of temperature by the electron beam induced current (EBIC) method. Based on the lifetime vs temperature characteristics, we classify the defects into three macroscopic (> 20 μm scale) categories: (i) plastically deformed single crystal region; (ii) dislocation arrays with associated impurity atmosphere; and (iii) crystallographic structural line boundaries including twins and grain boundaries. The recombination processes described by category (ii) include a set of shallow electron donor traps near the dislocation core with apparent activation energies E_c − E_t = 0.066−0.087eV. The recombination lifetime of category (iii) can be described by Shockley-Read-Hall statistics with a recombination level located at the lower half of the band gap. Under the measurement condition, the activation energies of the acceptor-like center in category (iii) were found to be E_t − E_v = 0.086−0.114 eV. The recombination properties of category (i) and (ii) defects are consistent with the presence of compensating donor states in the p-type ribbon. Thus, it is believed that these types of defects are primarily responsible for the observed minority carrier lifetime dependence on the photoexcitation level in the EFG ribbon silicon.     

多孔硅薄膜对p 型单晶硅太赫兹波段透射特性的影响

利用化学腐蚀方法,在低阻值p型单晶硅片上制备了火山口形、准纳米孔柱形和多孔形三种形貌的多孔硅薄膜。以空气为参考基准,0.2～10 THz时域光谱显示,火山口形样品在0.2～6 THz的透射强度下降了约1/2,另外两种样品强度下降了约1/5。火山口形、准纳米孔柱形样品呈现低通滤波特性,多孔形样品呈现级联带通特性。准纳米孔柱形样品截止频率比火山口形样品和多孔形样品提高了3 THz左右。样品的频谱出现多处吸收峰,峰的位置与薄膜的几何结构尺寸有关。实验结果表明:多孔薄膜的形状和几何结构尺寸改变了p型单晶硅的太赫兹波段透射强度、吸收频率和截止,该材料可以成为从太赫兹波段至可见光波段的宽频段探测材料和调制材料。     

Electrical measurement of electron and hole mobilities as afunction of injection level in silicon

The first experimental method to separately measure the hole and the electron mobilities as a function of the injection level is presented. The carrier mobilities are extracted from impulsive measurements of the resistance associated with a n⁺-ν-n ⁺ (p⁺-π-p⁺) structure, where the conductivity of the intermediate layer is controlled by the injection of an incorporated p-n junction diode. Two-dimensional numerical simulation is used to assess the accuracy of the proposed measurement technique. Experimental results obtained at room temperature on both n-type and p-type materials are presented and compared to existing analytical mobility models     

On the injection level dependence of the minority carrier lifetime in defected silicon substrates

In the literature several reports have indicated a strong increase of the minority carrier lifetime with injection level in defected single crystal and semi-crystalline silicon. These types of potentially low-cost materials are being developed for the photovoltaic industry. The lifetime increase, mainly observed at low injection levels, has usually been explained by the saturation of active traps with increasing injection level. However, a detailed experimental analysis of the recombination losses in materials showing this behavior, points to a strong local variation in the trap density, presumably associated with crystal microdefects. We demonstrate in this paper that the non-linearity of the recombination current at low illuminations observed in defected materials, can be explained by considering the recombination at grain boundaries and microdefects. The conditions are detailed under which the lifetime increases with injection level.     

Titanium in silicon as a deep level impurity

Titanium inserted in silicon by diffusion or during Czochralski ingot growth is electrically active to a concentration level of about 4 × 10¹⁴ cm^?3. Hall measurements after diffusion show conversion of lightly doped p type Si to n type due to a Ti donor level at E_C - 0.22 eV. In DLTS measurements of n⁺p structures this level shows as an electron (minority carrier) trap at E_C - 0.26 eV with an electron capture cross section of about 3 × 10^?15 cm² at 300°K. The DLTS curves also reveal a hole trap in the p type material. The e_p (300/T)² activation plot gives the level as E_V + 0.29 eV. The hole capture cross section is about 1.7 × 10^?17 cm² at 300°K and decreases with decreasing temperature and the corrected trap level becomes E_V = 0.26 eV. Ti in lightly doped (360 ohm-cm) n type material does not result in conversion to p type so this level is inferred also to be a donor.A Ti electrically active concentration of about 1.35 × 10¹³ cm^?3 in p type (N_A = 3.35 × 10¹⁵cm^?3) Si results in a minority carrier (electron) lifetime of 50 nsec at 300°K.