R. Baron

A new acceptor level in indium‐doped silicon

A new acceptor level located 0.111±0.002 eV from the valence band with a peak photoionization cross section of (1.4±0.6) ×10−16 cm2 has been observed in indium‐doped silicon. Its presence is revealed both by the low‐temperature slope of Hall measurements versus temperature and by the spectral response of the photoconductivity. The concentration of this 0.111‐eV level is strongly correlated with the concentration of indium, suggesting that an In complex is responsible for this center.

Nature of the 0.111‐eV acceptor level in indium‐doped silicon

Strong evidence is presented that the X‐level defect, which produces a 0.111‐eV acceptor level in Si : In, is a substitional In–substitutional C (Ins‐Cs) pair. The concentration of this defect follows a mass‐action law with the In and C concentrations, the association constant being (1.4±0.3) ×10−19 cm−3 at 650 °C. Reversible changes in the X‐level concentration between anneal temperatures of 650 and 850 °C are observed, and a pair binding energy of 0.7±0.1 eV is estimated. The electronic properties and temperature dependence of the concentration of this center are found to be those expected for a nearest‐neighbor Ins‐Cs pair.

Effects of Diffusion and Thermal Generation on Double Injection in Semiconductors

The theoretical treatment of the double‐injection semiconductor regime has been extended to include first diffusion and then both diffusion and thermal generation. When only diffusion is included, the results parallel earlier results for the insulator regime. Large deviations from the simple Lampert theory are found even when the sample length L is as great as 50 times the ambipolar diffusion length La. The electric field distribution is characterized by exponentially increasing regions from the boundaries in which e∝ exp |x/La|, merging into a central region which approximates the Lampert distribution e∝(x—x0)1/2. The current—voltage characteristic approximately follows a I∝V2+s law, where s is a monotonically increasing function of La/L, the magnitude of the current being larger than predicted by Lampert. The inclusion of thermal generation leads to a very large transition region between the Ohmic and high‐level regimes. For values of the ratio τl/τ≳10 between low‐level and high‐level lifetimes, this re...

Transient Response of Double Injection in a Semiconductor of Finite Cross Section

The transient response of the current to an applied voltage step is analyzed for a structure exhibiting double‐injection behavior, subject to the condition that both initial and final states are describable by the same double‐injection regime. The analysis is carried out for both the one‐dimensional case (no surface recombination) and the case of a two‐dimensional slab (surface recombination included). For the one‐dimensional case, the response is an Ohmic current step followed by an exponential decay with a time constant equal to the high level, common lifetime. For the two‐dimensional case the response is similar, except that the decay following the current step is described by a sum of exponential decays with time constants determined by the transverse modes of the system. The time constant for the longest lived mode is not equal to the effective lifetime found by Hiroto et al. for the steady‐state case, but may differ from it by as much as 23.4%. The high level photoconductive decay is also analyzed f...

Double Injection in Long Silicon p—π—n Structures

Current—voltage characteristics and electric field distributions have been measured in a series of long silicon p—π—n structures biased into the double injection regime. The I—V characteristics obey an I∝V2/L3 relation in which the magnitude of the current is predicted within a factor of two by the Lampert expression. As predicted by Baron (in the preceding paper) it is necessary to correct for diffusion effects. A first‐order correction can be made by the use of an effective length Leff=L—Q(2La), where La is the ambipolar diffusion length. The field distribution approximates the Lampert region in the center (e∝x1/2) bounded by exponential regions due to carrier diffusion from the n—π and p—π junctions. Detailed analysis indicates that the observed I∝V2 region was not due to pure high‐level double injection, but rather exhibits the transition region due to both diffusion and thermal generation. Further, the measured lifetime is greater by about a factor of two than the lifetime required for an exact fit t...

DEEP (1–10 μ) PENETRATION OF ION‐IMPLANTED DONORS IN SILICON

Deep penetration of donors has been observed as a result of 20‐kV Sb ion implantations into 〈110〉‐ and 〈111〉‐oriented, high‐resistivity silicon. The density profiles were measured by a capacitance‐voltage method. The deep penetrating tail was found to be independent of such experimental parameters as temperature of implant (for T ≥ 300°C), orientation, annealing, and surface condition; and to empirically follow a N ∝ (x + B)2.2 dependence over four orders of magnitude (B ≈ 0.15 μ). This component has not been observed previously in silicon and has a different dependence on implantation parameters and a different functional form than that observed in ion channeling.

Differential Step Response of Unipolar Space‐Charge‐Limited Current in Solids

The small signal step response of unipolar space‐charge‐limited current in solids is analyzed for planar structures and for media in which the drift velocity of the charge carriers is either proportional to the electric field (thermal charge carriers) or is independent of the electric field (hot charge carriers). Results are reported in analytical and graphical form. Their features are discussed in terms of the underlying physical phenomena, as well as in the perspective of experimental applications. Cylindrical and spherical structures are not accessible to closed‐form solutions by the approach.

THE ELECTRICAL BEHAVIOR OF IMPLANTED BISMUTH IN SILICON

The electrical behavior of 20–50‐keV Bi implanted layers in silicon has been evaluated using Hall effect and sheet resistivity measurements. Implants of greater than 1014/cm2 performed at room temperature show a large increase in the number of carriers/cm2 for short anneals at ≈600°C that is associated with the reordering of the lattice. Although Rutherford scattering measurements (performed at Chalk River Nuclear Laboratories) indicate that ≈80% of the Bi atoms are substitutional, only ≈20% are effective electrically. The peak value of the carrier density distribution is ten times the corresponding maximum solid solubility.

Breit-Wigner-Fano resonances in the photoconductivity of semiconductors: Experiment

Abstract We report the observation of new structure in the photoconductivity spectra of the single acceptors (B, Al, Ga, and In) in Si. This structure occurs at frequencies corresponding to an energy equal to the excitation energy of bound P su 3 2 states from the ground state plus the energy of a near zone center optical phonon. Based on this observation the structure is attributed to Breit-Wigner-Fano resonances due to the mixing of the excited bound states of the acceptor plus an optical phonon with the continuum of unbound states.

Neutron Transmutation Doping of p-Type Czochralski-Grown Gallium Arsenide

We have studied the neutron transmutation doping process in bulk GaAs grown by the liquid encapsulated Czochralski technique. By choosing undoped, but initially p-type samples for irradiation, we observed the effects of transmutation doping with Se and Ge donors both at low doping levels as added compensation in p-type samples, and at higher doping levels as added donors in n-type samples. We found that a measurable fraction of NTD-produced Ge atoms act as acceptors rather than donors in our material.