V. Higgs

Characterization of epitaxial and oxidation‐induced stacking faults in silicon: The influence of transition‐metal contamination

Photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and defect etching have been used to characterize epitaxial stacking faults (ESF) in silicon epilayers grown by low‐pressure chemical vapor deposition (LPCVD) and oxidation‐induced stacking faults (OISF) in high‐purity float‐zone (FZ) Si. No dislocation‐related luminescence was observed from either ESFs or OISFs grown under clean conditions. Deliberate surface contamination, followed by annealing with Cu, Fe, Ni, Ag, or Au in the range 4×1012–2×1016 atoms cm−2 introduced dislocation luminescence features, with a maximum intensity at ≊4×1012 atoms cm−2. TEM examination revealed that there was no evidence for precipitation at low levels of contamination but as the contamination level increased metal‐related precipitates were observed on the bounding partial dislocations.

Cathodoluminescence imaging and spectroscopy of dislocations in Si and Si1−xGex alloys

Dislocations in float‐zone Si which has been plastically deformed and deliberately copper contaminated, and misfit dislocations in a relaxed Si1−xGex alloy layer grown on a Si substrate by molecular beam epitaxy, have been investigated by monochromatic and panchromatic cathodoluminescence imaging and by cathodoluminescence spectroscopy. The measurements show that the D3 and D4 luminescence features originate on the slip lines in plastically deformed Si and at the misfit dislocations in the Si1−xGex alloy layer whereas the D1 and D2 bands are dominant between the slip lines and the misfit dislocations.

Metal‐induced dislocation nucleation for metastable SiGe/Si

A new mechanism of misfit dislocation nucleation is demonstrated. Deliberate contamination with approximately 0.003 monolayers of Cu and subsequent annealing at 600 °C is shown by transmission electron microscopy, photoluminescence, and defect etching to produce dislocation half loops in a 1.1 μm layer of Si0.93Ge0.07 on a silicon substrate.

Photoluminescence from MBE Si grown at low temperatures; donor bound excitons and decorated dislocations

Donor bound exciton luminescence has been detected in silicon grown by molecule beam epitaxy at 550 degrees C and 750 degrees C with an intensity comparable with that observed in silicon grown from the melt with a similar electrically active donor concentration. Therefore, the strong suppression of luminescence from electrically active impurities reported in previous investigations is not an inherent property of MBE silicon grown at low temperatures and must be associated with the presence of other contaminants. The major inadvertent electrically active dopant is seen to be phosphorus in the material investigated. The relative strength of the bound exciton luminescence from the epitaxial layers and that arising in the substrate can be varied by heat treatment and deliberate contamination by transition metals. The latter treatment is also seen to result in the appearance of dislocation D-band luminescence which is not observed in the as-grown material, implying that D-band luminescence is associated with decorated as distinct from undecorated dislocations.

Investigation of the recombination activity of misfit dislocations in Si/SiGe epilayers by cathodoluminescence imaging and the electron beam induced current technique

Misfit dislocations in as‐grown and Ni‐contaminated Si/SiGe epilayers have been characterized by cathodoluminescence (CL) spectroscopy, cathodoluminescence imaging, and the electron beam induced current technique (EBIC). Dislocations in the as‐grown layers had no radiative recombination (D bands) and no detectable room temperature EBIC contrast. Following Ni contamination the D bands were observed and the EBIC contrast increased. CL dark line contrast is observed by monochromatic imaging of the Si substrate luminescence. The CL dark line contrast was observed from all the dislocations, whether contaminated or as grown. The CL dark line contrast and EBIC contrast show a 1:1 correspondence of the nonradiative recombination at the misfit dislocation and also a semiquantitative agreement with the variation in measured contrast of the individual dislocations.

Photoluminescence characterization of molecular beam epitaxial silicon

Abstract A review is given of the photoluminescence observed from silicon grown by molecular beam epitaxy (MBE), with particular emphasis on recent work on material grown at temperatures carried out by the authors. The areas addressed are distinguishing between luminescence originating in the epitaxial layer and in the substrate, complexes formed by the incorporation of carbon and nitrogen, the suppression of bound-exciton luminescence from electrically active impurities and the effects of gettering by dislocations, and dislocation-related luminescence and the effects of transition metal contamination. It is shown that the suppression of bound-exciton luminescence from electrically active impurities is not an inherent property of MBE silicon grown at low temperatures and must be due to the presence of contaminants. The nature of the contaminants responsible and the mechanism of luminescence quenching has not been identified. It is also shown that dislocation-related D-band luminescence is associated with dislocations decorated by transition metals as distinct from undecorated dislocations.

Luminescence from rod-like defects and hydrogen related centres in silicon

Abstract An account is given of some preliminary investigations of the luminescence associated with the creation of rod-like defects in Czochralski silicon, and centres produced by radiation damage which contain hydrogen. The aim of the work on rod-like defects is to try and obtain a better understanding of the optical centres associated with extended defects. One of the aims of the work on hydrogen related centres is to provide an analytical tool for understanding the chemistry of hydrogen in silicon.

Effect of hydrogenation on the luminescence of strained Si1−xGex alloy layers grown by molecular beam epitaxy

Thick Si1−xGex strained alloy layers grown by molecular beam epitaxy (MBE) are investigated using photoluminescence (PL) spectroscopy. Near‐band‐edge luminescence with well resolved phonon structures is observed for both as‐grown and deuterated samples. The low energy broad band frequently encountered in MBE‐grown alloy layers is shown to be annihilated by deuteration, giving rise to the no‐phonon and phonon‐assisted near‐band‐edge PL peaks. The broad band recovers by annealing at T≥360 °C while the intensity of the near‐band‐edge luminescence vanishes. Secondary ion mass spectroscopy and the effect of deuterium passivation are used to help locate and assign the defects responsible for the low PL efficiency of MBE‐grown thick SiGe layers.

Traps for excitons and interstitial atoms in edge‐defined film‐fed growth silicon

We show from the power dependence of photoluminescence of as‐grown edge‐defined film‐fed film‐grown silicon (EFG Si) that there are few additional nonradiative traps for excitons in EFG Si relative to electronic grade silicon. The first application of cathodoluminescence topography to EFG Si reveals only a small (10%) decrease in the luminescence at grain boundaries from radiation‐damage centers at grain boundaries. A radiation‐damage complex formed by migration of an interstitial carbon atom is shown to be created, and also destroyed, at rates very similar to those in electronic grade silicon, indicating the absence of interstitial traps specific to EFG Si.

Characterization of Si/Si1−xGex/Si quantum wells by cathodoluminescence imaging and spectroscopy

Cathodoluminescence (CL) imaging and spectroscopy have been used to characterize fully strained SiGe quantum wells grown on Si. At T≊5 K, the CL spectra contain only band edge luminescence features. Monochromatic imaging with the no‐phonon line attributed to the bound excitons in the quantum well, has shown that the distribution of the luminescence from the wells is not uniform. The thinnest well (33 A) contained a low density of nonradiative (luminescence reduction up to 100%) spots 40–100 μm in size. The thickest well (500 A) contained similar nonradiative spots and also dark line features oriented along the 〈110〉 directions. These dark line features are areas of nonradiative recombination (up to 70%) and have been identified by transmission electron microscopy as misfit dislocations.