J.‐P. Noël

Intense photoluminescence between 1.3 and 1.8 μm from strained Si1−xGex alloys

Intense photoluminescence (PL) from strained, epitaxial Si1−xGex alloys grown by molecular beam epitaxy is reported with measured internal quantum efficiencies up to 31% from random alloy layers, single buried strained layers, and multiple quantum wells. Samples deposited at ∼400 °C exhibited low PL intensity, whereas annealing at ∼600 °C enhanced the intensity by as much as two orders of magnitude. This anneal treatment was found to be optimal for removal of grown‐in defect complexes without creating a significant density of misfit dislocations. PL peak energies at 4.2 K varied from 620 to 990 meV for Ge fractions from 0.53 to 0.06, respectively. Efficient PL was due to exciton accumulation in the strained Si1−xGex layers of single and multiple quantum wells, where the band gap was locally reduced. Optical transitions associated with the PL occurred without phonon assistance.

Luminescence origins in molecular beam epitaxial Si1−xGex

Interstitial‐type features smaller than ∼1.5 nm and in areal densities up to 7×108 cm−2 have been identified as the origin of a broad photoluminescence (PL) band from thick, fully strained layers of Si1−xGex alloys grown by molecular beam epitaxy. The strong PL band was predominant when the alloy layer thickness was greater than 4–10 nm, depending on x and the growth temperature. Thinner alloy layers exhibited phonon‐resolved transitions originating from shallow dopant bound excitons, similar to bulk material but shifted in energy due to strain and hole quantum confinement.

High quantum efficiency photoluminescence from localized excitons in Si1−xGex

We report a new photoluminescence process in epitaxial Si1−xGex layers grown on Si by rapid thermal chemical vapor deposition which we attribute to the recombination of excitons localized at random alloy fluctuations. This luminescence is characterized by saturation at very low excitation densities (≂100 μW cm−2), very long decay times (≳1 ms), and high quantum efficiency at low excitation. We have directly measured an external photoluminescence quantum efficiency of 11.5±2%.

Electroluminescence and photoluminescence from Si1-xGex alloys

Electroluminescence has been observed from Si1−xGex/Si p‐n heterostructures grown by molecular beam epitaxy and fabricated into mesa diodes. The luminescence from each sample was observed at temperatures up to 80 K with diodes forward biased at current densities up to 50 A/cm2. For x=0.18 and x=0.25, broad (∼80 meV) electroluminescence peaks were observed at 890 and 860 meV, respectively. These energies as well as the peak shapes and quantum efficiencies (∼1%) were the same as those from corresponding photoluminescence spectra.

Exciton luminescence in Si1−xGex/Si heterostructures grown by molecular beam epitaxy

Coherent Si1−xGex alloys and multilayers synthesized by molecular beam epitaxy (MBE) on Si(100) substrates have been characterized by low‐temperature photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Phonon‐resolved transitions originating from excitons bound to shallow impurities were observed in addition to a broad band of intense luminescence. The broad PL band was predominant when the alloy layer thickness was greater than 40–100 A, depending on x and the strain energy density. The strength of the broad PL band was correlated with the areal density (up to ∼109 cm−2) of strain perturbations (local lattice dilation ∼15 A in diameter) observed in plan‐view TEM. Thinner alloy layers exhibited phonon‐resolved PL spectra, similar to bulk material, but shifted in energy due to strain and hole quantum confinement. Photoluminescence excitation spectroscopy, external quantum efficiency, time‐resolved PL decay, together with the power and temperature dependence of luminescence inten...

Visible photoluminescence from biexcitons in Si1-xGex quantum wells

Abstract We have observed visible photoluminescence, at photon energies nearly twice those of the usual near-infrared excitonic emissions, from thin Si 1-x Ge x quantum wells at liquid He temperatures. This confirms that a significant biexciton population is present in such samples under excitation conditions normally used for near-infrared photo-luminescence measurements. The intensity of the visible luminescence increases linearly with excitation density, consistent with the biexcitons being localized by fluctuations in alloy content. The biexciton lifetime is observed to vary with the Si 1-x Ge x quantum well width indicating an enhancement of the overlap of the particle wave functions by the quantum confinement.

Measured In-plane hole drift and hall mobility in heavily-doped strained p-type Si1−xGex

Measured in-plane hole drift and Hall mobilities in heavily boron-doped strained Si1−xGex layers are reported. In the range of boron dopings examined (1.5–2.1 × 1019 cm−3), the drift mobility is seen to increase with increasing germanium fraction. The Hall mobility decreases with increasing germanium fraction.

Novel infrared detector concept utilizing controlled epitaxial doping profiles

A novel infrared detector concept is proposed and experimentally demonstrated. Because of the flexibility provided by modern epitaxial growth techniques, we use thin heavily doped Si layers for infrared absorption via free‐carrier‐related processes, and the active region is sandwiched in a p‐n junction. Silicon‐based materials for long‐wavelength infrared applications are highly desirable because of the possibilities for advanced Si circuit technology.

Electroluminescence and photoluminescence from Si1−xGex alloys grown on (100) silicon by molecular beam epitaxy

Abstract Photoluminescence has been observed from Si 1− x Ge x alloy layers, superlattices and non-periodic multilayers where x was varied from 0 to 0.6 A p-type Si 0.82 Ge 0.18 alloy layer 200 nm thick, grown by molecular beam epitaxy (MBE), has been fabricated into a mesa diode which operated as a light-emitting diode, emitting at 1.4 μm at temperatures up to 80 K. This diode was selected from a series of heterostructures which exhibited intense photoluminescence with internal quantum efficiencies in the range 1%–10% at low temperatures. Photoluminescence in the wavelength range 1.2–1.7 μm has been observed from thick (100–200 nm) Si 1− x Ge x alloys and Si 1− x −Si strained layer superlattices with a range of dimensions which was large compared with the unit cell; i.e. where Brillouin zone folding effects were negligible. The intense Si 1− x Ge x alloy photoluminescence peak had a halfwidth of about 80 meV and the peak energy was found to shift consistently and predictably with the germanium fraction. Photoluminescence peak energies at 4.2 K varied from 620 to 990 meV for germanium fractions where 0.53 > x > 0.06. The photoluminescence and electroluminescence peaks were consistently about 120 meV below the established bandgap for tetragonally strained Si 1− x Ge x . In general, Si 1− x Ge x strained layers grown at low temperatures typical of MBE (below 500°C) exhibited low photoluminescence intensity. However, post-growth annealing in the 500–700°C temperature range enhanced luminescence efficiency by up to two orders of magnitude. A comparison is also made of the broad intense photoluminescence observed from MBE material with the weak near-band-edge spectra obtained from Si 1− x Ge x -Si grown by low temperature chemical vapour deposition.

Photoluminescence spectroscopy of localized excitons in Si 1-x Ge x

We have recently found that high quantum efficiency can be achieved in strained Si1−xGex alloy layers through the elimination of nonradiative channels. We observed a photoluminescence process in SiGe grown on 〈100232A; silicon by rapid thermal chemical vapor deposition, which was attributed to free excitons localized by random fluctuations in alloy composition. The external quantum efficiency of this process was measured directly for a single Si0.75Ge0.25 quantum well and found to be extraordinarily high, about 11.5 ± 2%. In this paper, we present additional data on the localized exciton photoluminescence, including temperature dependence, time decay curves, and effects of sample annealing.