I. D. Hawkins

Laplace transform deep‐level transient spectroscopic studies of defects in semiconductors

A quantitative improvement in deep‐level transient spectroscopy (DLTS) resolution has been demonstrated by using Laplace transform method for the emission rate analysis. Numerous tests performed on the software used for the calculations as well as on the experimental setup clearly demonstrated that in this way the resolution of the method can be increased by more than an order of magnitude. Considerable confidence in this approach was gained through measurements of a selection of well‐characterized point defects in various semiconductors. The results for platinum in silicon and EL2 in GaAs are presented. For each of these cases conventional DLTS give broad featureless lines, while Laplace DLTS reveals a fine structure in the emission process producing the spectra.A quantitative improvement in deep‐level transient spectroscopy (DLTS) resolution has been demonstrated by using Laplace transform method for the emission rate analysis. Numerous tests performed on the software used for the calculations as well as on the experimental setup clearly demonstrated that in this way the resolution of the method can be increased by more than an order of magnitude. Considerable confidence in this approach was gained through measurements of a selection of well‐characterized point defects in various semiconductors. The results for platinum in silicon and EL2 in GaAs are presented. For each of these cases conventional DLTS give broad featureless lines, while Laplace DLTS reveals a fine structure in the emission process producing the spectra.

Electronic properties of vacancy–oxygen complex in Ge crystals

It is argued that the vacancy-oxygen (VO) complex (A center) in Ge has three charge states: double negative, single negative, and neutral. Corresponding energy levels are located at E-c-0.21 eV (VO--/-) and E-v+0.27 eV (VO-/0). An absorption line at 716 cm(-1) has been assigned to the asymmetrical stretching vibration mode of the doubly negatively charged VO complex

The determination of valence band discontinuities in Si/Si1−xGex/Si heterojunctions by capacitance‐voltage techniques

Capacitance‐voltage (C‐V) profiling has been used to measure the apparent carrier concentration profiles in Si/Si1−x Ge x /Si structures for a range of Ge percentages. Using Kroemers analysis, good agreement has been found between theoreticalvalence band offsets and those determined from the experimental data. The validity of Kroemers analysis has been assessed in the presence of traps using a C‐V simulation program. Under certain circumstances, large errors occur in the extracted valence band offset due to distortion of the apparent carrier concentration profile by traps. It is proposed that the experimental data presented here falls into a regime where minimal distortion is to be expected and is reflected by the accuracy of the extracted valence band offsets.

LAPLACE-TRANSFORM DEEP-LEVEL TRANSIENT SPECTROSCOPY STUDIES OF THE G4 GOLD-HYDROGEN COMPLEX IN SILICON

We have studied n-type silicon containing gold and gold–hydrogen complexes using high-resolution “Laplace” deep-level transient spectroscopy. This technique has enabled two quite distinct electron emission rates to be observed at temperatures between 240 and 300 K. These are associated with the gold acceptor and the level referred to as G4, which is observed when hydrogen and gold are present in silicon. The gold acceptor has a measured activation energy for electron emission of 558±8 meV, and the G4 state of 542±8 meV. The directly measured electron capture cross section for G4 is determined to be 0.6±0.1 σn(gold acceptor) at 275 K from which it is inferred that the state is acceptor-like.

The impact of negative-bias-temperature-instability on the carrier generation lifetime of metal-oxynitride-silicon capacitors

N-type metal-oxynitride-silicon capacitors were subjected to a negative bias voltage at an elevated temperature. Under this condition, Negative-bias-temperature-instability (NBTI) was evidenced in capacitance-voltage (CV) characteristics with an accompanying decrease, as determined from inversion layer-related (i.e., generation lifetime) deep-level-transient-spectroscopy (DLTS) measurements, in the carrier generation lifetime. An analysis of the dominant defect supplying minority carriers to the inversion layer at the silicon-oxynitride interface revealed a significant change brought about by NBTI. A full recovery of the carrier generation lifetime was observed after several days at zero bias voltage, and room temperature conditions had elapsed following NBTI. Concurrently, a passivation, as inferred from conventional DLTS measurements, of the NBTI-induced trap density occurred at the silicon-oxynitride interface. These relaxation and deactivation phenomena were discussed in the context of a plausible mod...

Energy state distributions of the Pb centers at the (100), (110), and (111) Si∕SiO2 interfaces investigated by Laplace deep level transient spectroscopy

The energy distribution of the Pb centers at the Si∕SiO2 interface has been determined using isothermal laplace deep level transient spectroscopy. For the (111) and (110) interface orientations, the distributions are similar and centered at 0.38eV below the silicon conduction band. This is consistent with only Pb0 states being present. For the (100) orientation, two types of the interface states are observed: one similar to the (111) and (110) orientations while the other has a negative-U character in which the emission rate versus surface potential dependence is qualitatively different from that observed for Pb0 and is presumed to be Pb1.

Characterization of Si/Si1−xGex/Si heterostructures by capacitance‐transient spectroscopy

Deep level distributions have been investigated in B‐doped Si/Si1−xGex/Si layers grown by molecular beam epitaxy using deep level transient spectroscopy. Broadening in the deep level spectra is discussed in terms of carrier emission over a band of deep level energies as has been considered for both alloy disorder and dislocations. The distortion observed in the deep level spectra in the vicinity of the upper Si/Si1−xGex heterojunction is suggested to be a consequence of the significant band bending that occurs in this region; the possible causes for this distortion are discussed. The deep states exhibit donor‐like behavior and the origin of the electrical activity is considered to lie with metal point‐defect/dislocation interactions.

A comparison of the photoluminescence decay of erbium in silicon and silicon-germanium

Photoluminescence decay times have been measured from n- and p-type silicon, a Si/Si 1-x Ge x (x = 13%) multi quantum well structure, all implanted with Er, and a Si/Si 1-x Ge x (x = 25%) MQW structure uniformly doped with Er during MBE growth. The decaying PL signal is recorded using a signal-averaging transient capture card, and decays over nearly three decades are acquired with a system response time of 10 μs. The Er luminescence is much more intense in the Si/SiGe MQW structures than in silicon hosts. The method of Er-doping in the Si/SiGe heterostructures does not alter the PL decay significantly, but only one component is observed in the decay transient from the Er doped SiGe structures, compared with two in the PL decay of Er doped Si.

The electrical assessment of p-isotype Si/SiGe/Si heterostructures grown by MBE

Abstract Si/Si 0.9 Ge 0.1 heterostructures have been analyzed using the Capacitance-Voltage (C-V) technique described by Kroemer. A valence band offset of approximately 70 ± 10 meV was deduced, in good agreement with that predicted by other methods. The significant deep level populations revealed by deep level transient spectroscopy and variable temperature C-V methods have a comparatively small effect upon the deduced offset.

Separation of dislocation- and erbium-related photoluminescence by time resolved studies

Abstract The luminescence of Er in silicon occurs at 1.54 μm, which is very close to the dislocation-related PL signal in silicon known as D1. Photoluminescence decay measurements have been carried out on silicon co-implanted with Er and O. Decays were recorded using a transient capture card designed in-house, and decays over nearly three decades were routinely measured with a system response time of 10 μs. The decay transient always shows a component with a decay time of up to 1100 μs, and also a component with a much faster decay time. It is shown, that the presence of the fast decay component correlates with a broadening of the signal at 1.54 μm, indicative of radiative emission due to the dislocation-related line D1, and also with the observation in electron and optical microscopy of small extended defects.