Diffusion of interstitial magnesium in dislocation-free silicon

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 10¹⁴ and 2 × 10¹⁵ cm^–2. The diffusion coefficient of interstitial magnesium donor centers (D _i ) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence D _i (T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.     

Radiation-induced bistable centers with deep levels in silicon <Emphasis Type="Italic">n</Emphasis> <Superscript>+</Superscript>–<Emphasis Type="Italic">p</Emphasis> structures

The method of deep level transient spectroscopy is used to study electrically active defects in p-type silicon crystals irradiated with MeV electrons and α particles. A new radiation-induced defect with the properties of bistable centers is determined and studied. After keeping the irradiated samples at room temperature for a long time or after their short-time annealing at T ～ 370 K, this defect does not display any electrical activity in p-type silicon. However, as a result of the subsequent injection of minority charge carriers, this center transforms into the metastable configuration with deep levels located at E_V + 0.45 and E_V + 0.54 eV. The reverse transition to the main configuration occurs in the temperature range of 50–100°C and is characterized by the activation energy ～1.25 eV and a frequency factor of ～5 × 10¹⁵ s^–1. The determined defect is thermally stable at temperatures as high as T ～ 450 K. It is assumed that this defect can either be a complex of an intrinsic interstitial silicon atom with an interstitial carbon atom or a complex consisting of an intrinsic interstitial silicon atom with an interstitial boron atom.     

Dependence of dicarbon annealing temperature in <Emphasis Type="Italic">n</Emphasis>-Si on oxygen concentration in the crystal

The role of oxygen in the mechanism of dissociation of the dicarbon complex in n-Si into components is considered. It is assumed that released interstitial carbon atoms C_i migrate through the crystal and react with both substitutional carbon C_s and interstitial oxygen with the resulting formation of complexes C_iC_s and C_iO_i, respectively. The solution of a system of equations describing the formation of interstitial carbon atoms in the course of annealing of dicarbon show that the rate constant for the reaction of annealing of the C_iC_s complex (the G center) depends on the oxygen concentration. This dependence is treated as the dependence of the activation energy for annealing of a C_iC_s complex and, consequently, the dissociation energy of this complex on oxygen concentration. A more accurate value of dissociation energy for the G center was determined as 1.08±0.03 eV.     

A comparison of MOS gate structures formed by depositing polycrystalline silicon on thin oxides using conventional low pressure chemical vapor deposition and rapid thermal chemical vapor deposition

MOS structures with 80Å-200Å thick gate oxides were fabricated using polycrystalline silicon gate electrodes deposited by rapid thermal chemical vapor deposition (RTCVD) and by conventional chemical vapor deposition (LPCVD). Polycrystalline silicon doping was achieved by BF₂ or As implantation followed by rapid thermal annealing (RTA). The Q-C method was employed to study the electrical properties of the capacitors through high and low frequencyC- V profiles. The electrical properties of the MOS structures show that the devices fabricated using RTCVD polycrystalline Si are comparable in quality to those with LPCVD polycrystalline silicon gate electrodes. However, the results also indicate that boron diffusion through the thin oxide is a problem regardless of the deposition technique used for polycrystalline silicon. Boron penetration is accompanied by a shift in threshold voltage, inversion layer capacitance and a high density of midgap interface traps. Dopant diffusion in polycrystalline silicon and through the thin gate oxides was also studied by secondary ion mass spectroscopy (SIMS). The findings of the SIMS analysis correlate well with the electrical measurements. The results indicate that significant boron diffusion can occur through an 80A oxide if an RTA temperature higher than 1000° C is used. On the other hand, both SIMS and electrical measurements suggest that As penetration into the substrate is negligible even at temperatures as high as 1100° C.     

Dissociation energies of a C<Subscript>i</Subscript>C<Subscript>s</Subscript> complex and the <Emphasis Type="Italic">A</Emphasis> center in silicon

Reactions of annealing of A centers (VO) and complex centers consisting of interstitial carbon atoms and substitutional carbon atoms (C_iC_s) in n-Si irradiated with fast electrons or ⁶⁰Co gamma quanta were analyzed. The kinetics of isochronous annealing of the above centers was evaluated. By comparing the results of calculations with published experimental data, which were obtained by measuring the concentration of centers with the level E_c?0.17 eV in the course of isochronous heat treatment of irradiated n-Si, the dissociation energy E for the C_iC_s complex was estimated at 1.10±0.05 eV. The activation energy for annealing of this center was found to be equal to \(E_{aC_i C_s } \approx 2.0eV\). The dissociation energy for the A center was estimated at E_A=1.94 eV.     

Planar microcavity containing luminescent diamond particles with embedded silicon-vacancy color centers in its active layer

A planar hybrid microcavity containing isolated diamond particles with embedded silicon-vacancy (Si-V) color centers in its active layer is fabricated by plasma-enhanced chemical vapor deposition. Distributed Bragg reflectors are produced on the basis of alternating quarter-wave a-Si_{1 ? x} C _x :H and a-SiO₂ layers. The color centers are controllably introduced from the gas phase during the course of growth of the diamond particles. A narrowing to 5 nm of the zero-phonon line at a wavelength of 738 nm and suppression of the phonon wing in the photoluminescence spectrum of the Si-V color centers are achieved.     

Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H₂ are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225°C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 × 10–4% O₂ is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H₂ is added. The values obtained for the activation energy of the silicon diffusion coefficient, E _a = 2.57 eV, and for the exponent n = 3.31–3.74 in the time dependence of the pore radius, r ~ t ^1/n are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.     

Base doping and recombination activity of impurities in crystalline silicon solar cells

The optimisation of base doping for industrial crystalline silicon solar cells is examined with model calculations. Focus is on the relation between base doping and carrier recombination through the important impurities interstitial iron (Fe_i) and the metastable boron–oxygen (BO) complex. In p‐type silicon, the optimum base resistivity is strongly dependent on defect concentration. In n‐type silicon, recombination due to Fe_i is much lower and nearly independent of resistivity. Fe_i is likely representative for other transition metal impurities. In many real cells a balance between Fe_i or similar defects, and BO will occur. Copyright © 2004 John Wiley & Sons, Ltd.     

Nonmonotonic variations in the concentration of the donor-and acceptor-type radiation defects in silicon irradiated with low-intensity fluxes of β particles

Deep-level transient spectroscopy is used to study the dependence of the concentration of the donor-and acceptor-type radiation defects in silicon on the duration of irradiation with low-intensity fluxes of β particles (I ≈ 9 × 10⁵ cm^?2 s^?1). It is found that the concentrations of the defects C _i , C _i -C _s , and/or V-O in n-Si and the defects V-B, C _i -O _i , and/or V ₂-O-C in p-Si vary nonmonotonically.     

Accelerated Light-Induced Degradation (ALID) for Monitoring of Defects in PV Silicon Wafers and Solar Cells

In crystalline silicon, above-bandgap illumination can transform defects into strong recombination centers, degrading minority-carrier lifetime and solar cell efficiency. This light-induced degradation (LID) is due primarily to boron–oxygen and iron–boron defects, and can be reversed using thermal treatments that are distinctly different for each type of defect. Combining illumination and thermal treatment, we have designed an accelerated light-induced degradation (ALID) cycle that, within minutes, transforms defects into the distinct states needed to isolate individual contributions from boron–oxygen dimers (BO_2i) and interstitial iron (Fe_i). In this cycle, the concentrations of BO_2i and Fe_i are determined using surface photovoltage (SPV) diffusion length measurement. The ALID cycle uses reversible defect reactions and gives very good repeatability of wafer-scale mapping of BO_2i and Fe_i in photovoltaic (PV) wafers and final solar cells.     

A study of recombination centers in irradiated <Emphasis Type="Italic">p</Emphasis>-Si crystals

p-Si samples irradiated with 8-Mev electrons are studied. It is suggested that the multicomponent V₃+O or V₂+O₂ complexes are not recombination centers on the basis of an analysis of the dependences of the minority-carrier lifetime τ, the resistivity ρ, the concentration p, and the Hall mobility μ_H on the temperature of isochronous annealing T_ann. Deep donors with energy levels at ΔE_i=E_v+0.40 eV and the V₃+O₃ and the V₃+O₂ complexes affect the values of μ_H and τ. The curves of isochronous annealing are used to determine the annealing-activation energies E_ann for defects such as K centers, interstitial carbon atoms C_i, the V+B and V₂+O₂ complexes, divacancies V₂, and defects with a level at ΔE_i=E_v+0.20 eV. These energies were found to be equal to E_ann=0.9, 0.25, 1.6, 2, 1.54, and 2.33 eV, respectively.     

Performance of 12-μm- to 15-μm-Pitch MWIR and LWIR HgCdTe FPAs at Elevated Temperatures

Infrared (IR) focal-plane arrays (FPAs) with higher operating temperatures and smaller pitches enable reduced size, weight, and power in infrared systems. We have characterized a large number of medium- and long-wavelength IR (MWIR and LWIR) FPAs as a function of temperature and cutoff wavelength to determine the impact of these parameters on their performance. The 77-K cutoff wavelength range for the MWIR arrays was 5.0 μm to 5.6 μm, and 8.6 μm to 11.3 μm for the LWIR. The dark currents in DRS’s high-density vertically integrated photodiode (HDVIP)^® FPAs (based on a front-side- illuminated, via-interconnected, cylindrical-geometry N+/N/P architecture) are dominated by Auger-7 recombination from 120 K to 200 K for the MWIR and 70 K to 100 K for the LWIR. In these temperature ranges the FPA operability is generally limited not by dark current defects but by noise defects. Pixels with high 1/f noise should produce a tail in the root-mean-square (rms) noise distribution. We have found that the skewness of the rms noise distribution is the simplest measure of an array’s 1/f noise, and that the rms noise skewness typically shows little variation over these temperature ranges. The temperature dependence of the defect counts in normal arrays (wet etched prior to CdTe interdiffusion) increases as n _i, while nonstandard arrays (ion milled or plasma etched prior to CdTe interdiffusion) can have high 1/f noise and defect counts that vary as n _i ² . Our models indicate that, if the dominant dark current is due to diffusion, then the 1/f noise varies as n _i ² , whereas if depletion current dominates, then the 1/f noise varies as n _i. Systemic 1/f noise is not an issue for DRS’s standard MWIR FPAs at 110 K to 160 K, or for standard LWIR FPAs at 77 K to 100 K.     

Electrical Characteristics of Al/Poly(methyl methacrylate)/p-Si Schottky Device

Al/Poly(methyl methacrylate)(PMMA)/p-Si organic Schottky devices were fabricated on a p-Si semiconductor wafer by spin coating of PMMA solution. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of Al/PMMA/p-Si structures have been investigated in the frequency range of 1 kHz–10 MHz at room temperature. The diode parameters such as ideality factor, series resistance and barrier height were calculated from the forward bias current–voltage (I–V) characteristics. In order to explain the electrical characteristics of metal–polymer–semiconductor (MPS) with a PMMA interface, the investigation of interface states density and series resistance from C–V and G–V characteristics in the MPS structures with thin interfacial insulator layer have been reported. The measurements of capacitance (C) and conductance (G) were found to be strongly dependent on bias voltage and frequency for Al/PMMA/p-Si structures. The values of interface state density (D _it) were calculated. These values of D _it and series resistance (R _s) were responsible for the non-ideal behavior of I–V and C–V characteristics.     

Effects of mesa area and orientation on defects in strained InxGa1−xAs films grown by LPOMCVD

We have selectively grown In_xGa_1?xAs (0.04 <x < 0.20, 200 ? 7000Å) on rectangular growth areas (100 μm by 200 mil) patterned on GaAs substrates with very low etch pit densities (～200 cm^?2). The edge orientations of the growth areas were varied on the substrate resulting in distinct facet formation on the deposited mesa structures. Layers were grown using Low-Pressure Organometallic Chemical Vapor Deposition (LPOMCVD) and all samples were annealed for 1 hr at 700° C. Indium content and film thicknesses were very uniform across a wafer so that only the facet shape was varied. Observation of Crosshatch defect densities as a function of growth window orientation showed that 2900Å In_0.08Ga_0.92As mesas with [010] edge orientations exhibited no Crosshatch defects. Identical mesas grown in windows with other edge orientations exhibited varying crosshatch defect densities. Large unpatterned areas of growth were heavily crosshatched. This variation in Crosshatch defect density as a function of mesa orientation appears to be associated with non-area related dislocation nucleation mechanisms at the mesa edges. Proper choice of window orientation for patterned substrate epitaxy will allow the mesa facets to be controlled thereby reducing misfit dislocations in the heterostructure interface.     

Low-temperature instabilities of the electrical properties of Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te:Cl semi-insulating crystals

The electrical properties in the temperature range 295–430 K and low-temperature (4.2 K) photoluminescence of Cd_1?xZn_xTe:Cl semi-insulating crystals grown from melts with a variable impurity content (C _Cl ⁰ = 5 × 10¹⁷–1 × 10¹⁹ cm^?3) are investigated. Nonequilibrium processes leading to a decrease in carrier concentration are observed in all the samples at low temperatures (T = 330–385 K). These changes are reversible. The activation energy of these processes E _a is found to be 0.88 eV. As with semi-insulating CdTe:Cl, the observed phenomena can be explained by a change in the charge state of background copper atoms: Cu_Cd ? Cu_i. The introduction of Zn changes the ratio of the concentrations of shallow-level donors Cu_i and Cl_Te from their levels in the initial material.     

Electronic properties of variably charged defects in crystalline semiconductors

The electronic properties of defects with various spatial configurations are examined in relation to corresponding sets of valence bonds. The examination is based on the analysis of the energy functional, in which the elastic energy in the anharmonic approximation, the variation in the electronic term of the defect quasi-molecule defined by the electron localization, and Hubbard’s interaction energy are taken into account. Two types of such defects are recognized, namely, the defects with strong and weak electron-atom interaction. For defects of the first type, which are characterized by positive effective correlation energy, no variations of the adiabatic potential topology are observed after the electron localization. The pair of carbon atoms (C_iC_s) and donor-acceptor pairs in the crystalline silicon belong to this type of defect. The effective occupancy is calculated for this type of defects as a function of adiabatic potential parameters. Transformation of the initial double-well potential into the single-well potential after the localization of the carriers is substantial for the properties of the second type defects. In this case, the effective correlation energy can be either positive or negative. The analysis of the known experimental results permits us to assume that the interstitial boron atom in silicon belongs to this type of defect. The adiabatic potential (in which the interstitial boron atom moves), the activation energies for transitions between different charge states of this defect, and the effective occupancy are calculated from the experimental data reported by Watkins.     

Features of the band structure and conduction mechanisms of <Emphasis Type="Italic">n</Emphasis>-HfNiSn heavily doped with Y

The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, N _A ^Y ≈ 1.9 × 10²⁰–5.7 × 10²¹ cm^–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf_1–x Y _x NiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.     

Electrically-detected electron paramagnetic resonance of point centers in 6H-SiC nanostructures

The results of investigation of electrically-detected electron paramagnetic resonance (EDEPR) and classical electron paramagnetic resonance (EPR) (X-band) for the identification of shallow and deep boron centers, NV _Si defects, and isolated silicon vacancies (V _Si), which are formed directly during the preparation of planar nanostructures under conditions of silicon-vacancy injection at the SiO₂/n-6H-SiC interface without any subsequent irradiation, are presented. The prepared sandwich nanostructures are an ultra-narrow p-type quantum well, confined by δ barriers heavily doped with boron on an n-6H-SiC surface, which are self-ordered during pyrolytic-oxide deposition and subsequent short-time boron diffusion. The EDEPR data of point centers in sandwich nanostructures, prepared within the framework of Hall geometry, are recorded by measuring the field dependences of the magnetoresistance without an external cavity, microwave source and detector, due to the presence of microcavities embedded in the quantum-well plane and microwave generation under conditions of a stabilized source-drain current from δ barriers containing dipole boron centers. The obtained EDEPR spectra of the shallow and deep boron centers are analyzed using the data of EPR studies in 6H-SiC bulk crystals [10]. The EDEPR spectrum of the isolated silicon vacancy reveals both the negatively charged state V _Si ^? (S = 3/2) and the neutral state in hexagonal (V _Si(h)) and quasicubic (V _{Si(k1, k2)}) states (S = 1). In turn, NV _Si defects are detected not only by the EDEPR method at 77 K, but also through the use of a Bruker ELEXSYS E580 EPP spectrometer at 9.7 GHz, in a temperature range of 5–40 K. The EDEPR and EPR spectra recorded on the same sandwich nanostructure are virtually identical and correspond to the center in the triplet state with spin S = 1. The EPR spectrum, which is a lowintensity line doublet with a splitting value equal to ΔB = 237.6 mT, is observed in the background of the EPR spectrum from donors of nitrogen, the concentration of which in the n-6H-SiC initial sample was 5 × 10¹⁸ cm^?3, whereas nitrogen donor centers are not revealed in the EDEPR spectrum because of total occupation by silicon vacancies inside the 6H-SiC sandwich nanostructure.     

Detection of hydrogen impurity in silicon radiation detectors

The behavior of silicon particle detectors irradiated with 2.5-MeV electrons during subsequent annealing is studied. Annealing at 100–250°C was found to result in the formation of two types of traps with the levels E _c ?0.32 eV and E_v+0.29 eV. Increasing the annealing temperature to 300°C makes both traps disappear. On the basis of data obtained, it was concluded that these traps are related to hydrogen-containing complexes. The presence of hydrogen in a crystal results in a decrease in the annealing temperature for vacancy-oxygen (VO) complexes and complexes consisting of carbon and oxygen interstitials (C_iO_i). The reason for this phenomenon is the passivation of these complexes by hydrogen, which results in the formation of electrically active VOH centers {with the level E _c ?0.32 eV} in an intermediate stage of this process. It is assumed that hydrogen penetrates the structures under investigation in one of the stages of their fabrication.     

Formation kinetics of various types of hydrogen-related donors in proton-implanted silicon

The method of C-V characteristics has been used to study the accumulation kinetics of double and shallow hydrogen-related donors in proton-implanted epitaxial silicon. It is shown that the kinetics corresponds to the first-order reactions. The activation energies ΔE ₁ = 2.3 eV and ΔE ₂ = 1.4 eV and the pre-exponential factors τ₀₁ = 9.1 × 10^?17 s and τ₀₂ = 4.2 × 10^?9 s were determined for both types of the donors, respectively. It was shown that the bistability of the electric properties of silicon is due to the double hydrogen-related donor.