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.

The growth of erbium doped gallium arsenide by MBE at normal substrate temperatures (~580°C) is constrained by a solubility limit of 8×1017 cm−3. This is much less than is desirable for optical emitters using the forbidden 4f transitions of Er3+ to produce radiation at 1.54µm. We have developed an MBE technique where it is possible to produce spherical mesoscopic precipitates containing erbium as a matrix element within the gallium arsenide. Structural and analytical studies indicate that the precipitate is cubic (rock salt) erbium arsenide. The physical size of the precipitates is self limiting as a result of surface migration occurring during MBE growth. By adjusting the growth conditions it is possible to produce an array of uniform erbium arsenide quantum dots of a size chosen from the range 10–20Å. The dot density can be varied by changing the erbium flux.

This paper reviews our recent experimental work on erbium incorporated into gallium arsenide during MBE growth. The electrical behaviour of the erbium is considered in relation to its interaction with intentionally added dopants (silicon, selenium and berylium) and the effect of the erbium on the deep state population is discussed. At higher concentrations the morphology of phase separation is considered and results are presented showing the controlled precipitation of erbium arsenide as quantum structures. The magnetic properties of these dots and wires are reported.

Deep level transient spectroscopy (DLTS) of n-type, molecular beam epitaxially grown GaAs has revealed a large increase in the concentrations of the characteristics deep electron traps, known as M states, with erbium doping. Total M trap concentrations in excess of 5 × 1015 cm-3 are measured for a moderate erbium doping level of 1 × 1018 cm-3. These high M trap concentrations can be increased by a further two orders of magnitude by growth upon strained, more heavily erbium-doped material. Dilation of the GaAs matrix, arising in this case from the presence of the large Erbium atoms and ErAs precipitates in the lattice, is believed to play a major role in the creation of these characteristics MBE defects.

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.