Dominant Recombination Center Research Articles

Proton irradiation of silicon: Complete electrical characterization of the induced recombination centers

The control of minority-carrier lifetimes in n-type silicon by means of low-dose, high-energy proton irradiation at room temperature has been investigated. The irradiation-induced defects, their electrical properties, their annealing behavior, and their relevance for carrier lifetimes have been studied by deep level transient spectroscopy (DLTS) and the open-circuit voltage decay technique. Emphasis was placed on the complete electrical characterization of the dominant recombination centers induced by the proton bombardment of silicon. The energy level position within the forbidden band, the capture cross sections, and emission rates for majority and minority carriers, as well as the defect concentration were determined for each center. By means of a special recombination selective DLTS measurement mode (double-double DLTS) it was even possible to localize in the spectra the deep centers which are relevant to minority-carrier lifetimes. The results are quantitatively discussed in the framework of Shockley–Read–Hall recombination statistics with respect to the reduction of carrier lifetimes for high- and low-injection conditions in semiconductor devices. The results have been corroborated qualitatively by the correlation of the minority-carrier lifetimes in proton-irradiated devices with the concentrations of the induced recombination centers which were influenced by different temperature treatments.

Role of the mid-gap level as the dominant recombination center in platinum doped silicon

The problem of identification of the dominant recombination center in platinum-doped silicon is investigated using deep-level transient spectroscopy (DLTS). Measurements using electrical and optical injection on platinum-doped n type silicon are reported. Results of measurements show that the recently observed platinum-related midgap level is an efficient recombination center and is probably responsible for the role of platinum as a lifetime killer. In addition, information is provided on the relative magnitudes of the electron and hole capture cross sections of the hitherto well-known deep levels assigned to platinum.

A Novel Approach to the Assessment of Semiconductor Hetero-Interfaces in Multilayer Structures

ABSTRACTWe demonstrate the novel use of CV simulation to determine the level of charge at each interface in multilayer GaAs/AlGaAs heterostructures. The gettering of charged centres at the earliest grown interfaces is quantitatively appraised and the parallel application of PL decay lifetime measurements determines their effectiveness as recombination centres. A direct relationship is found between the magnitude of the charged states and the recombination velocity. Estimates of a 1eV activation energy and a hole capture cross section of 10−15 cm2 were also obtained. This suggests that the dominant recombination centre could be observed as a hole trap.

Improved Hole Diffusion Lengths in Bulk n-Type GaAs for High Efficiency Solar Cells

AbstractA method for wafer annealing which is effective in suppressing defects and raising minority carrier diffusion lengths in n-type bulk GaAs is described. The beneficial effect of the annealing is shown to be associated with the proximity surface with measurements of photoresponse as a function of depth. The concentration of the hole trap HCX (Ev+0.29eV) varies as a function of depth from the surface, qualitatively, as might be expected of the concentration of the dominant recombination center in the material. The impact of improving the material in this manner on the performance of Zn diffused solar cells is demonstrated.

Electron diffusion length in rapid thermal processed p-type silicon

Electron diffusion length in p-type virgin silicon has been measured by the surface photovoltage method after rapid thermal processing as a function of process time duration and process temperature. The results obtained are consistent with a model involving defects acting as a single dominant recombination center induced in the bulk. This recombination center is responsible for the severe degradation of the diffusion length, even at process temperatures as low as 600 °C. An activation energy of 1.48±0.28 eV is found for the center introduction rate. The work shows that the diffusion length measurement is a very sensitive tool in the study of rapid thermal process induced recombination centers in the bulk, with direct correlation to device performance.

Minority carrier diffusion lengths in bulkn-type gaas

Minority carrier hole diffusion lengths in as-grown and Ni- or Cu-diffused bulkn-GaAs, both LEC and HB, having carrier concentrations in the range 1016-1017cm−3 have been studied by surface photovoltage methods and trap concentrations determined by DLTS measurements. Data are available for a wide range of specimens and therefore a method of correlation ofLp with electron trap concentrations has been developed that allows easy identification of the dominant recombination center. This is determined to be the level at aboutEc-0.40 eV, termed EL5 in earlier studies of electron traps.

A STUDY OF ELECTRON IRRADIATION-INDUCED DEFECTS IN Si LAYERS

The experiments were done using p+u junction irradiated with 12MeV electron. Pour electron traps were observed in Si layers: A-center E1(Ec -0.19 eV), the divaeancy E2 (Ec -0.24 eV), and E4 (Ec -0.44 eV), and E3 defect level (Ec- 0.37eV). Using DLTS method in conjuntion with the reverse recovery technique, annealing behavior of E1, E4 and E3 traps have been studied. The annealing temperature of the E3 defect is the highest (≈520℃). We get an activation energy for thermal annealing of 1.71 eV with a frequency factor of ～1.5×109s-1. The E3 and E4 defect levels are the principal recombination center that controls lifetime of minorities following irradiation. As the E2 and E4 defect level annealout, however, defect level E3 becomes the dominant recombination center.

Dislocation-Solute Interactions at Twin Boundaries in Dendritic Web Silicon

ABSTRACTDLTS, TEM and APFIM techniques have been used to study impurity-defect interactions responsible for reducing minority carrier diffusion lengths in solar cells of dendritic web silicon. Fine scale precipitates of SiOx, which decorate dislocations piled up at the twin planes in low eff clency cells, appear to be the dominant recombination centers.

Temperature dependence of the hole lifetime in n-type GaP

The minority carrier lifetime has been measured at single dislocations in n-type GaP. From the temperature dependence of the dislocation lifetime we found a dominant recombination centre at a level 0.15eV which is, probably, associated with S-donor/Cu complexes.

The connection between carrier lifetime and doping density in nondegenerate semiconductors

It is assumed that there exists a temperature Tf at which dominant recombination centers in the form of electrically neutral, mechanical defects (e.g., vacancies) are frozen into a semiconductor matrix. For this process we assume an Arrhenius-type law with an activation energy. From this assumption there follows by standard semiconductor statistics the doping dependencies of (a) the defect concentration and (b) the minority carrier lifetimes. The analysis can in principle be applied to any defect in any semiconductor which satisfies the above assumptions, provided the cross sections and related data are known. For the case of silicon we have deduced a set of parameters to fit the optimal experimental lifetimes. Assuming the unknown defects to have two charge states, neutral and negative, it is inferred that the levels lie near midgap and have recombination coefficients of order 10−9 cm3 s−1.

Charge-carrier recombination in silicon irradiated with γ-rays of different energies

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Ion-implantation associated defect production in silicon

Defects produced during ion implantation have traditionally been removed during high temperature (⩾ 1200 K) thermal processing. The current industry trend towards lower temperature processing will require new techniques for suppressing defect formation associated with ion implantation. This paper details the characterization and identification of the electrically active defects which are produced during low dose ion implantation. Several of the observed defect levels can be correlated with defects which have been identified in electron irradiated silicon. However, a defect level near mid gap, H(0.53), which should be the dominant recombination center in p-type samples, cannot be correlated with previously identified defects. Similarly, the H(0.20) level is found to anneal near 420 K, and thus does not correlate well with the known properties of the divacancy, which introduces a similar trapping level.

Deep-state-controlled minority-carrier lifetime in n-type gallium phosphide

Details of a method for the characterization of deep levels with large capture cross sections for minority carriers are presented. This technique has been used to investigate centers in gallium phosphide. Two defects at EV+0.75 eV and EV+0.95 eV are described in detail. Evidence is presented that shows that the shallower of these defects can control the minority-carrier lifetime in n-type gallium phosphide and in fact is the dominant recombination center in most epitaxial layers of this material. The technique uses capacitance as a measure of the charge state of the deep levels in the depletion region of a Schottky barrier. This charge state is perturbed by the capture and subsequent thermal emission of minority carriers. The carriers are generated by irradiation of the semiconductor with low-intensity light at a wavelength near the absorption edge. Minority carriers generated in the neutral material within about a diffusion length of the barrier region are extracted by the depletion field. Majority carriers are excluded by the field and consequently the current through the barrier is due predominantly to minority carriers. These are captured by the defects, the fastest capture being into the levels with the largest capture cross sections. As a result, the technique can in many cases be used selectively to detect the most important recombination centers in a semiconductor and to determine their capture cross sections, concentrations, and energy depths.

The Dominant Recombination Centers in Electron‐Irradiated Semiconductors Devices

The defect states introduced by electron irradiation of silicon and the effects these defect levels have on low level minority carrier lifetimes have been studied by the capacitance transient spectroscopy and reverse recovery techniques. The E3 defect level is the principal recombination center that controls lifetime following room temperature irradiation. As the E3 defect level anneals, however, a secondary defect level E4 emerges which then becomes the dominant recombination center. This defect level E4 is related to the electron‐induced defects since it is not produced in unirradiated samples. The energy levels and capture cross sections of these electron‐induced defects are reported.

Electrical properties of platinum in silicon as determined by deep-level transient spectroscopy

Platinum was diffused into p+nn+ and n+pp+ silicon diodes at temperatures ranging from 860 to 910 °C for approximately 1 h. Using deep-level transient spectroscopy, six levels associated with platinum in these silicon devices were detected. Ev+0.19 eV, Ev+0.28 eV, Ev+0.33 eV, Ev+0.41 eV, Ec−0.34 eV, and Ec−0.23 eV. The concentrations, thermal emission rates, and the capture cross sections for majority carriers at these defects are reported. The Ec−0.34 eV level has not been previously characterized but is probably the dominant recombination center.

Effect of III/V Ratio on the Properties of Vapor Phase Epitaxial GaP

The effect of III/V ratio in the gas stream on the properties of grown by the vapor phase epitaxial (VPE) technique has been studied. At the substrate temperature of 840°C, the nitrogen distribution coefficient is found to increase strongly with increasing III/V ratio. Equilibrium thermodynamic calculations explain the dependence well. On the other hand, the residual doping level, believed to be due to S, has the opposite dependence on III/V ratio which is not understood. The minority carrier lifetime and diode efficacy are observed to increase with III/V ratio. An analysis of this behavior indicates the dominant nonradiative recombination center in this material may be a deep acceptor residing on the Ga sublattice, such as Cu or Fe.

Electroluminescence in semiconductors

This brief review is restricted to a selection of very recent work on bulk properties of commercially important III–V compound semiconductors, mainly GaP and GaAs1-xPx. Some recent theoretical and experimental work on electronhole binding suggests the importance of correlation for isolated N in GaP. The band structure enhancement of the optical efficiency of N in GaAs1-xPx has received clarification. Recent advances in our understanding of the electronic binding energies of the dominant shunt path recombination centres and their relationship with dislocations are reviewed, mainly for LPE GaP.

A technique for the investigation of deep-level states in diffused p—N junction devices: Application to GaAs electroluminescent diodes

Analytical equations describing the high-frequency (1 MHz) capacitance-voltage ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C-V</tex> ) characteristics have been derived for diffused p-n junction diodes, including the effect of deep-level states within the bandgap. It was found that the C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> versus <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</tex> curve becomes nonlinear when the density of the deep-level states is large. From the derived <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C-V</tex> equation the density of the deep-level states may be calculated from the slope of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C^{3}V</tex> versus <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C(V- V_{2})/V^{2}</tex> curve, where V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> is related to the energy level of the deep states. The value of V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> may be determined from the recombination current versus temperature measurements at small bias. The theory has been applied to characterize the dominant deep-level recombination centers in Zn-diffused GaAs light-emitting diodes. The measured deep levels are within 0.2 eV of the midgap energy and the density of these centers is of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .

Recombination Centers in Gamma-Irradiated Silicon

The minority carrier lifetime in gamma-irradiated silicon crystals was studied. The doping impurity was phosphorus, arsenic, or boron, and the crystals were either float-zoned or pulled from the melt. The silicon E center was found to be the dominant recombination center in float-zoned, n-type crystals after irradiation. The capture cross section of the center for holes was measured to be 1.1×10−13 cm2 in phosphorus-doped silicon. The activation energy for annealing of an E center has been reported to be 0.94 eV, and the corresponding activation energy for the annealing in arsenic-doped crystals was found to be 1.5 eV. After annealing at 160°C, where the E center is known to anneal, the existence of some other energy level at about 0.4 eV below the conduction band was detected. In crystals other than float-zoned n-type, the A center governed the recombination. The cross section of this center was found to be 1.5×10−14 cm2 for holes and 2×10−16 cm2 for electrons. The introduction rate of the A center was found to be the same for a variety of samples. The value was 1.3×10−3 defects/cm3 per photons/cm2.

Characteristics of silicon p- n junctions formed by sodium and cesium ion bombardment

Silicon n- p junction rectifiers and photodiodes have been formed by sodium and cesium ion bombardment of acceptor doped silicon. The devices formed by this new technique are well described by present junction theory. The position of the dominant recombination centers, near the intrinsic Fermi level, and a mean carrier recombination lifetime in the depletion region may thus be deduced from the forard current-voltage characteristics. The mean recombination lifetime may be near that found in diffused junctions. Capacitance measurements indicate the presence of an effective region of nearly linear impurity grading near the junction. Reverse breakdown measurements give values consistent with this conclusion. The spectral dependence of the photodiode response is characteristic of thin junction structures.