Kenneth B Joelsson

Er/O and Er/F doping during molecular beam epitaxial growth of Si layers for efficient 1.54 μm light emission

Er, together with oxygen or fluorine as co-dopants, has been incorporated into Si during molecular beam epitaxial growth using co-evaporation of Si and Er containing compounds. The Er doping concentration using both Er2O3 and ErF3 can reach a level of ∼5×1019 cm−3 without precipitation, which is at least one order of magnitude higher than a previously reported solid solubility limit for Er in Si. Growth, structural, and luminescence characterization of these Er/O and Er/F doped Si samples are reported. In particular, 1.54 μm electroluminescence has been observed from Er/O doped Si layers at room temperature through hot electron impact excitation.

Room temperature 1.54 μm light emission of erbium doped Si Schottky diodes prepared by molecular beam epitaxy

Schottky-type light emitting devices have been fabricated on Er-oxide doped Si layers grown by molecular beam epitaxy, in order to study the light emission process of Er-doped Si structures. By applying a reverse bias on the Schottky junction, Er ions incorporated within the depletion layer can be electrically excited via a hot electron impact process. Rather intense electroluminescence (EL) at a wavelength of 1.54 μm has been observed at room temperature. The optoelectronic properties of the devices have been characterized by both input-power dependent and temperature dependent EL measurements. An activation energy value of ∼160 meV responsible for luminescence thermal quenching has been obtained.

A silicon molecular beam epitaxy system dedicated to device-oriented material research

Abstract Design, performance test, doping capability and grown material quality of a Balzers UMS 630 Si MBE system are reported, particularly concerning measures to obtain good quality of grown films. Good stability, reproducibility and uniformity of deposition rates (Si and Ge) and doping concentrations (Sb and B) have been obtained for growth on a 4 inch Si wafer with sample rotation using a mass-spectrometry controlled e-beam evaporation system, and home-made doping sources, respectively. The quality of grown undoped and modulation doped Si and SiGe layered structures were evaluated using high-resolution XRD, XTEM, SIMS, Hall, and PL measurements. Intense and sharp excitonic PL transitions and high carrier mobility obtained from the grown Si SiGe heterostructures and quantum wells grown at a wide substrate temperature range (320–650°C) indicate high crystalline quality of grown films. Finally, test HBT structures with a thin SiGe base have been made. Good dc characteristics and frequency performance were obtained.

Growth of high quality Ge films on Si(111) using Sb as surfactant

High quality, completely relaxed Ge films have been grown on Si(111) using Sb as surfactant at the initial stage of growth. After desorbing the surface Sb layer, cusplike reflection high‐energy electron diffraction intensity oscillations indicated excellent Ge layer‐by‐layer epitaxy. High resolution x‐ray diffraction analysis showed a very high crystalline quality and well resolved thickness fringes consistent with a flat relaxed Ge layer. Chemical preferential etching experiments revealed a defect density of down to ∼3×104 cm−2.

Characterization of highly boron-doped Si, Si1 − xGex and Ge layers by high-resolution transmission electron microscopy

Abstract Cross-sectional transmission electron microscopy (XTEM) has been used to characterize the defect structure of as-grown and annealed highly boron-doped Si, Si 1 − x Ge x ( x ≤ 0.18) and Ge layers grown by molecular beam epitaxy. The structures have also been analyzed with two-dimensional (2D) reciprocal space mapping using high-resolution X-ray diffraction (HRXRD). The boron concentration ( C B ) was in the range from 3 × 10 19 to 8 × 10 20 cm −3 . Si and Si 1 − x Ge x layers were grown at 400°C and Ge layers at 325°C. XTEM micrographs show no crystalline defects in Si and Si 1 − x Ge x samples for C B ≤ 3 × 10 20 cm −3 . However, for C B = 8 × 10 20 cm −3 , B precipitation in the form of epitaxial layer (2D) precipitates on (001) planes in Si and Si 1 − x Ge x and both (001) and (113) planes in Ge was observed. After annealing the B-doped Si and SiGe samples with C B = 8 × 10 20 cm −3 at 1000°C for 15 min, a large number of discrete, 3D, B-related precipitates were observed. For B-doped Ge samples, the thermal stability was poor and B precipitation and severe roughening were observed after annealing at 650°C for 15 min.

HIGH QUALITY SI/SI1-XGEX LAYERED STRUCTURES GROWN USING A MASS-SPECTROMETRY CONTROLLED ELECTRON-BEAM EVAPORATION SYSTEM

High quality, strained Si/Si1−xGex layered structures have been grown at temperatures in the range 400–625 °C, using a solid‐source molecular‐beam epitaxy (MBE) system with a mass‐spectrometry‐based loop‐control to improve the accuracy and stability of the evaporation rates. Good control of the growth parameters has been achieved as verified by, e.g., high‐resolution x‐ray diffraction. Very high intensities and extremely small peak widths, down to 2.7 meV for the XNP transition at low excitation levels of photoluminescence spectra, indicate high crystalline quality of the layers. It is shown that some previously reported defect‐related luminescence from MBE‐grown SiGe layers is not intrinsic to the MBE process.

Si1−yCy/Si(001) heterostructures made by sublimation of SiC during silicon molecular beam epitaxy

Preparation of pseudomorphic Si1−yCy/Si(001) heterostructures using Si molecular beam epitaxy with C obtained from SiC sublimation in a high-temperature cell has been studied. Thick (≈2000 A) homogenous Si1−yCy layers, y⩽1.5%, and Si1−yCy/Si multiple quantum well (MQW) structures, y⩽8%, have been prepared. There is a growth temperature dependent surface roughness accumulating during the growth sequence that can lead to reduction of C induced strain. Temperature modulation during growth has been used to suppress this effect. Near band gap photoluminescence is reported from Si1−yCy/Si MQW structures.

Injection of self-interstitials during sputter depth profiling of Si at room temperature

Samples consisting of multi B delta layers and a single Sb delta layer, grown using molecular beam epitaxy, have been sputter depth profiled using O2+ ions with incidence energy of 8.2 or 3.2 keV. The leading and the trailing edge of the B distributions show an anomalous broadening induced by the sputtering, which apparently increases with ion energy. Similar feature is not observed for the Sb distribution. Incorporation of substitutional C to concentrations ∼1019 cm−3 suppresses the broadening feature almost completely. This anomalous broadening is interpreted as a consequence of injection of Si self-interstitials from the region damaged by the ion bombardment. These interstitials may migrate far beyond the mixing depth and interact with the B dopants, which yields a mixing of the B atoms before the distribution is within the “ordinary” mixing depth.

Electroluminescence studies of Er and SiO co-doped Si layers prepared by molecular beam epitaxy

Abstract Er/O co-doped Si light emitting diodes (LEDs) have been fabricated using layer structures prepared by molecular beam epitaxy (MBE). The Er/O doping was realized by sublimation of elemental Er and silicon monoxide simultaneously with Si during MBE growth. Intense Er-related electroluminescence (EL) at 1.54 μm was observed at room temperature from p + -SiGe/i-SiGe-Si/Si:Er/n + -Si LEDs by electron impact excitation under reverse bias. It has been found that the EL intensity was increased with increasing growth temperature of the Si:Er/O layer in the range of 430–575°C. The electrical pumping power dependence of EL intensity has been studied. An excitation cross section value of ∼1×10 −16 cm 2 was estimated based on the experimental data and model fitting. The EL decay behavior under various injection and bias conditions has been studied by time-resolved EL measurements. The overall luminescence decay time is found to strongly depend on the injection parameters. Two types of de-excitation mechanisms due to Auger energy transfer to free carriers introduced by either dopant ionization or carrier injection have been discussed. Both Auger processes play an important role in reduction of the EL intensity when there is a high density of carriers with excited Er ions.

Lattice distortion in dry-etched Si/SiGe quantum dot array studied by 2D reciprocal space mapping using synchrotron X-ray diffraction

Abstract Using synchrotron X-ray two-dimensional reciprocal space mapping around the (004) and (224) reciprocal lattice points, we have studied the changes of the lattice strain in a 30-period 3 nm Si/3 nm Si 0.7 Ge 0.3 superlattice (SL) that has been processed into a φ ≈50 nm columnar dot array by e-beam patterning combined with reactive ion etching. It has been found that the superlattice within the columns was partially relaxed after nano-fabrication. The observation of high-order SL satellites from columnar dots indicates a good long-range ordering of SL layers. An analysis based on elastic theory showed that the strain relief in the superlattice occurs by a partial relaxation in SiGe layers together with a biaxial lattice expansion in the thin Si layers, i.e. a strain symmetrisation effect. A staggered band line-up between Si and SiGe is then expected. We propose that an enhanced recombination between electrons and holes confined in adjacent quantum wells at the hetero-interfaces may give rise to the observed increase in the luminescence efficiency in this type of structures.