This paper reports the incorporation of erbium into MBE Si and Si/Ge alloys with substrate temperatures of 500°C and 700°C. Using a solid source MBE system, concentrations of erbium between 1018 and 1022 cm−3 have been studied by photoluminescence, electrical measurements, SIMS and TEM. We find no shallow donors or acceptors attributable to erbium but we observe a high concentration of deep states with an activation energy of ~360 meV. The photoluminescence output is of greatest magnitude when [Er] =2 × 1018 cm−3. Above this concentration the onset of erbium precipitates can just be observed using TEM and at even higher concentrations structured growths of erbium suicide are apparent. The effect on the optical activity of Si:Er that has subsequently been implanted with oxygen is also reported.

This paper reports a study of the non-radiative processes competing with the excitation of the erbium ion in layers implanted with high concentrations of erbium and oxygen. These processes reduce the luminescence efficiency of the Si:Er system and dramatically increase the threshold current density calculated to be necessary for an ultimate goal, the Si/Ge:Er LASER. Using cross sectional TEM, photoluminescence as a function of temperature and DLTS, it is demonstrated that a two stage anneal procedure which avoids the formation of extended defects and removes specific deep states is necessary to obtain efficient Er3+ excitation at high erbium concentrations. Comparisons are made with damage resulting from germanium implantation into silicon. The role of multiple stage anneals is discussed in relation to the removal of Shockley-Hall-Read recombination centres

A theoretical treatment of the minority carrier transient spectroscopy (MCTS) experiment is presented. We have modeled the minority carrier flux through the depletion region of an illuminated Schottky diode held under reverse bias, and used these data to calculate the occupancy of minority carrier traps as a function of energy, capture cross section, and temperature. The model shows that the capacitance transient monitored in the MCTS experiment decreases in intensity as the temperature is raised. It is demonstrated that this causes inaccuracies in the measured deep level activation energy Ea derived from an Arrhenius plot of the data. Simulated MCTS spectra have been compared with measured MCTS spectra of hole emission from the gold donor in silicon, and very good agreement between modeled and experimental spectra is observed. The model explains the commonly observed phenomenon of a reduction in MCTS peak heights for increasing temperature, which is the opposite effect from that commonly observed in conventional deep level transient spectroscopy data. It is shown that the correct choice of rate window can significantly reduce errors in the measured value of Ea.

Photoluminescence of silicon implanted with erbium and oxygen was measured in the time domain focussing on the temperature and excitation density dependence of the intra-4f-shell emission from Er3+. The decay of this luminescence is similar for the different optically active crystal field split Er-centres. At low temperatures the luminescence transients consist of a fast initial non-exponential component followed by slower exponential behaviour. An increase in excitation density results in a higher proportion of the luminescence decaying with the faster decay time. Our results indicate a relation of the fast component to nonradiative processes. Auger recombination is proposed as a possible mechanism.

A novel electron beam induced current (EBIC) technique, which utilizes two adjacent front contacts (one Schottky and one Ohmic), has been developed to characterize electrically active extended defects in the silicon overlayer of SIMOX structures. The results have been compared with photoluminescence measurements on the same samples. EBIC measurements on n-type SIMOX layers show that dislocations and precipitates present in the overlayer act as recombination centres. PL spectra exhibit dislocation-related emission, the intensity of which correlates with the change in density of extended defects measured by EBIC as the experiments are scanned across the wafer. P-type SIMOX material is found to contain stacking fault tetrahedra and pyramidals at the upper silicon-oxide interface and threading dislocations extending across the Si overlayer, but the PL emission of these defects is negligible. Thinning the overlayer by a sacrificial oxidation process creates oxidation-induced stacking faults in the overlayer, which give rise to strong dislocation-related PL emission. It is demonstrated that electrically active extended defects in the silicon overlayers of SIMOX structures are also optically active, and that PL measurements can provide a valuable insight into the electrical activity of the thin overlayers in these structures.

The capture kinetics of both electrons and holes at gold-hydrogen-related deep levels have been studied in n-type silicon using the techniques of deep-level transient spectroscopy (DLTS) and the related technique of minority carrier transient spectroscopy (MCTS). Four deep levels are observed in the bandgap, labelled G1 to G4. G1 and G4 are electron levels, and G2 and G3 are hole levels detected by MCTS that have previously been reported for gold-hydrogen complexes in p-type silicon. The combination of DLTS and MCTS in single-measurement techniques has enabled analysis of the carrier recombination processes occurring at the various deep levels by measuring the majority and minority carrier capture cross sections of each deep level. Based on this, it is proposed that a single type of Au-H defect is responsible for three of the observed levels, G1, G2 and G4, with the defect having a single donor (G2), and both single-(G4) and double-acceptor (G1) charge states. G3 is found to be a combination of two closely spaced levels with similar hole capture cross sections but different values of electron capture cross section.

As a preliminary to realising an Er-doped Si LED emitting at 1.54 mu m we have characterised silicon implanted with erbium over the dose range 5x10(13) cm(-2) to 1x10(15) cm(-2), coimplanted with oxygen or fluorine, and re-grown by a two stage anneal procedure. For the highest dose, damage accumulation results in a fully amorphous layer extending up to the surface, and transmission electron microscopy reveals that, after annealing, threading dislocations extend to the surface in these layers. Extended defects detected by TEM are shown to be optically active, and degrade the erbium-related luminescence.

Sharp luminescence at 1.54 mu m from erbium doped porous silicon has been observed. The silicon was made porous after implantation of high doses of erbium and oxygen into p-type Czochralski silicon. The erbium related luminescence from porous silicon is an order of magnitude more intense than that from erbium doped single crystal silicon.

We have characterised the recombination at Oxidation Induced Stacking Faults (OISF) by employing a combination of DLTS and Minority Carrier Transient Spectroscopy (MCTS). The recombination rate at traps associated with the OISF has been compared with recombination at a conventional point defect also present in the silicon. We find that the effect of small amounts of decoration by copper is to increase hole capture rates at electron filled traps. Infra Red Beam Induced Current measurements are consistent with this in that they also indicate that decoration causes enhanced recombination at the extended defects.

Majority and minority traps associated with oxidation induced stacking faults (OISFs) have been investigated by deep level transient spectroscopy and minority carrier transient spectroscopy. Electron and hole traps have been characterised in n and p type Si, and the activation energies of all extended defect related traps are found to be dependent on the occupancy of the state associated with the extended defect. Majority and minority carrier traps in n type Si exhibit non-exponential trap filling, which indicates the presence of a significant electrostatic barrier around the OISF. The electrical properties of hole (minority) traps measured by minority carrier transient spectroscopy in n type Si are found to be different from the deep level transient spectroscopy signature of hole (majority) traps in p type Si, and this is explained by examining differences between conditions during the measurements. By examining seperately the electron and hole capture properties of OISF related traps, one particular trap can be identified as a recombination centre. The capture cross-section of the OISF related hole trap in n type Si has been measured and it was found that, at low occupancy the trap captured cross-section is 7 x 10(-14) cm(2).

We have studied the effect of sub-band gap radiation on the defects associated with the Frank partial dislocation (Burgers vector a/3(111)) bounding oxidation-induced stacking faults (OISF) in n-type silicon. We have observed the contrast produced using IR-beam-induced current (IRBIC) and have studied the effect of the modification of the contrast of individual dislocations with below band gap radiation by quenched IR-beam-induced current (QIRBIC). We have compared these spectra with absolute measurements of the photocapacitance cross-section of the dominant deep state associated with the Frank partials. QIRBIC spectra for “clean”, gold-decorated and two levels of copper-decorated samples have been measured. A model of the recombination kinetics is discussed.

The synthesis of a buried layer of Si1−xGex alloy by combining high dose Ge+ implantation, amorphisation by high energy Si+ implantation and low temperature solid phase epitaxial regrowth is reported. A Si/Si1−xGex/Si heterostructure with graded interfaces and a maximum Ge concentration of 7.5 at.% has been successfully formed. The utility of amorphisation and low temperature solid phase growth across a graded phase boundary, as the last process step (EPIFAB) has been demonstrated. Examination of the sample by transmission electron microscopy has failed to resolve any crystallographic defects within the alloy layer, however, as expected, end-of-range defects are buried deep within the silicon substrate.

We have applied the technique of light-beam-induced transient spectroscopy, which characterizes minority carrier capture and emission at point and extended defects, to oxidation-induced stacking faults in n-type silicon. We have compared the minority carrier trap data with conventional deep-level transient spectra for majority carrier traps. We find that we are able to distinguish between hole capture at randomly distributed point defects (e.g Au), and hole capture at point defects which are associated with the extended-defect strain field.

The incorporation of erbium from a solid source into molecular beam epitaxy (MBE) Si and Si/Ge alloys grown at substrate temperatures of 500 degrees C and 700 degrees C has been studied by photoluminescence, electrical measurements, secondary-ion mass spectrometry (SIMS), Rutherford backscattering (RBS) and transmission electron microscopy (TEM). Erbium concentrations between 1018 and 1022 cm-3 were obtained but the maximum photoluminescence intensity was from samples with an erbium concentration of 2*1018 cm-3. Above this concentration the onset of erbium precipitation could just be observed by TEM. The authors found no shallow donors or acceptors attributable to erbium but they observed a high concentration of deep acceptors with an activation energy of 360 meV; these may be due to impurities in the erbium source rather than being directly related to the rare earth. Implantation with oxygen is found to enhance the Er3+-related photoluminescence signal when measured at temperatures greater than 77 K but to have little effect on the low-temperature luminescence. A detailed study of the temperature dependence of the luminescence reveals tree quenching mechanisms with average activation energies of approximately 5, 20 and 130 meV. The authors attribute the first two to de-excitation effects in the matrix, and the last to processes competing with the internal 4f transition.

The electrical and structural characteristics of secondary defects in regrown amorphous layers formed in n-type Si(100) with a resistivity of 2 Ω cm and 6 Ω cm using Ge+ ions, has been studied. The amorphous layers with a thickness of 460 nm are formed by implantation of 1 × 1015 Ge+ cm−2 at an energy of 400 keV. Both conventional furnace and rapid thermal annealing were used to regrow the amorphous layer and the residual defects have been characterised in terms of their concentration depth distribution and activation energies using C−V and DLTS. Structural information has been obtained from RBS and XTEM. By choosing suitable anneal conditions it is possible to eliminate extended defects, apart from a low concentration of end of range dislocation loops. However, a substantial population of electrically active point defects remain after simple low thermal budget anneals. In a sample implanted with 1 × 1015 Ge+ cm−2 at 400 keV a region of deep donors ∼ 460 nm from the surface is always present When the samples are annealed at higher temperatures (> 850° the total deep donor concentration is reduced by one order of magnitude. Other electrically active defects not observable in the low (750°C) temperature annealed layers become apparent during anneals at intermediate temperatures.

We have carried out photoluminescence (PL) on thin layers of silicon which have been pre-amorphised with a 400 keV germanium implant, and then subjected to rapid thermal annealing. TEM studies have established that the majority of extended defects were loops close to the original amorphous-crystalline boundary and that ∼ 90% of them are Frank type, 13a 〈111〉 dislocations. A dislocation related peak at 0.875 eV (the D2 line) occurred in most luminescence spectra. We have examined this as a function of anneal time and ambient atmosphere and we find that the D2 line strongly correlates with the Frank dislocation loops. This demonstrates that PL can be used as a diagnostic tool to detect Frank loops present in very thin silicon layers after ion implantation and annealing.

Observation of magneto-optical transitions in a Si center δ-doped quantum well is reported. The excitons are stabilized by the application of the field. With photoluminescence excitation spectroscopy (PLE), transitions below the Fermi level are observed. At magnetic fields ≳8 T broadened Landau levels can be seen. The features in the PLE spectra sharpen up significantly when the Larmor diameter becomes less than the average interimpurity spacing. The effect of the ionized donors in the well on the optical spectra is discussed.

It is well known that processing-induced defects in semiconductors can adversely affect device performance. This is particularly important for silicon, where oxidation processes can give rise to stacking faults along with other extended defects. A report is presented here of the relationship between the 'D' line dislocation-related photoluminescence (PL) lines, stacking fault length and the power of the laser employed as the excitation source. The authors have measured by PL a series of samples with different stacking fault lengths. Irrespective of stacking fault length they always observe lines D1 and D2 but no other higher-energy D lines; the intensity of the D lines increases with increased stacking fault length. The authors also find that the relative intensity of D2 to D1 depends upon the laser power employed in the PL experiment. The effect is observable in all their stacking-faulted samples and suggests that D1 and D2 are luminescence lines that originate from a related, if not the same, radiative process.

Presents a study of the electrical properties of deep states in silicon containing oxidation-induced stacking faults and dislocations. In general the electrical activity of stacking faults is associated with the Frank partial dislocation bounding it rather than the extra plane of the fault itself. In addition, the deep states associated with the partials of very clean stacking faults are rather ineffective as either generation or recombination centres. The authors have studied the effect of annealing oxidation-induced stacking faults in nitrogen and of decorating them with silver. After low-level decoration the defect states increase in concentration and the electron binding energy changes, tending to move the states towards the middle of the gap (hence increasing their effectiveness as generation centres). This level of decoration is not detectable with present-day TEM techniques. However, if the level of decoration is increased further, precipitates can be observed (using TEM) but the concentration of deep states decreases as does their electron binding energy. During this precipitative phase the intensity of the photoluminescence D lines is also seen to decrease substantially. These factors have a very considerable significance in relation to the imaging of extended defects using techniques which rely on recombination-generation effects and imply that the visibility of such defects is crucially dependent on the level of decoration.

Spatially direct radiative processes involving delta-doped planes are reported. The transitions are observed in structures that were designed to strongly confine holes to the delta-planes. Two structures, delta-plane superlattices and center-delta-doped quantum wells were used. In each case low-dimensional features associated with the modified subband structure were observed. The delta-plane superlattices exhibit electron minibands that may be "tuned" by control of the delta-plane spacing. Photogenerated holes are trapped in such structures and are unable to transport in the growth direction at low temperatures. The delta-doped quantum wells show grossly shifted confined states; for the heaviest doped well measured, the normal ordering of the n = 1 light-hole and the n = 2 heavy-hole states is reversed. Self-consistent calculations are reported, which account for the optical data in both types of structure.