Y. Lacroix

Defect‐free band‐edge photoluminescence and band gap measurement of pseudomorphic Si1−x−yGexCy alloy layers on Si (100)

Pseudomorphic Si1−x−yGexCy alloy layers on Si (100) with band‐edge photoluminescence and without defect‐related luminescence have been achieved. The photoluminescence was measured from 2 to 77 K and was used to make a direct measurement of the band gap shift as a function of strain reduction as C was added. Compared to the effect of just reducing Ge content, results show that as C is added, strain is reduced more efficiently than the band gap is increased. Furthermore, results imply that a fully strain‐compensated Si1−x−yGexCy layer on Si (100) would have a band gap much less than that of Si, and suggest that initial C incorporation reduces the band gap of relaxed, unstrained Si1−x−yGexCy alloys.

Low‐temperature photoluminescence of epitaxial InAs

Photoluminescence studies as well as reflectance and transmittance measurements were performed on high‐purity epitaxial InAs grown by metal‐organic chemical‐vapor deposition. We report the optical identification of excitonic, donor, and acceptor impurity related transitions at a temperature of 1.4 K. Measurements at higher temperature and in the presence of magnetic fields up to 7 T support these identifications. We find the excitonic band gap at 415.65±0.01 meV according to the minimum in the polariton reflectance feature. The donor–acceptor‐pair and acceptor‐bound exciton transitions for three different acceptors are observed by photoluminescence, and we tentatively associate one of them to a double acceptor formed by a Ga impurity on an As lattice site. A donor‐bound exciton transition is observed with a binding energy of 0.42 meV. The magnetic field dependence yields values of the electron effective mass and g factor of (0.026±0.002)m0 and −15.3±0.2, respectively, in good agreement with values obtaine...

Growth and photoluminescence of high quality SiGeC random alloys on silicon substrates

We report chemical vapor deposition growth of SiGeC layers on 〈100〉 Si substrates. At the growth temperature of 550 °C, the C concentration as high as 2% can be incorporated into SiGe (Ge content ∼ 25%) to form single crystalline random alloys by using low flow of methylsilane (0.25 sccm) as a C precursor added in a dichlorosilane and germane mixture. For intermediate methylsilane flow (0.5 sccm – 1.5 sccm), the Fourier transform infrared spectroscopy (FTIR) absorption spectra indicate the growth of amorphous layers. For the layers with high flow of methylsilane (12 sccm), there are silicon‐carbide‐like peaks in the FTIR spectra, indicating silicon carbide precipitation. The films were also characterized by x‐ray diffraction, high resolution transmission electron microscopy, secondary ion mass spectroscopy, and Rutherford backscattering spectroscopy to confirm crystallinity and constituent fractions. The defect‐free band‐edge photoluminescence at both 30 K and 77 K was observed in Si/SiGeC/Si quantum well...

Growth and band gap of strained 〈110〉 Si1−xGex layers on silicon substrates by chemical vapor deposition

We report chemical vapor deposition growth of strained Si1−xGex alloy layers on 〈110〉 Si substrates. Compared to the same growth conditions on 〈100〉 substrates, a slightly lower Ge composition and a much lower growth rate was observed. From photoluminescence measurements, the band gap of these films for 0.16≤x≤0.43 is evaluated and compared to theory. Finally, a surprisingly large ‘‘no‐phonon’’ replica line strength ratio was observed as compared with that observed in 〈100〉 layers.

DEEP PHOTOLUMINESCENCE IN SI/SI1-XGEX/SI QUANTUM WELLS CREATED BY ION IMPLANTATION AND ANNEALING

Strong broad photoluminescence similar to that observed in some materials grown by molecular beam epitaxy (MBE) has been observed in Si/Si1−xGex/Si quantum wells grown by chemical vapor deposition. As grown, the samples exhibited SiGe band‐edge phonon‐resolved bound‐exciton luminescence, but after being self‐implanted with silicon and annealed at 600 °C, a deep broad luminescence band 80–100 meV below the excitonic gap was observed. This strong luminescence disappeared with an 800 °C anneal and had a pump power and temperature dependence similar to that observed in MBE samples. This is the first time that such luminescence has been observed in material other than that grown by MBE.

Sharp excitonic photoluminescence from epitaxial InAs

The optically excited luminescence of epitaxial InAs has been studied at 1.4 K, revealing well‐resolved emission lines identified as the exciton–polariton, neutral–acceptor–bound exciton principal and two‐hole transitions, donor–acceptor pair band, and phonon assisted transitions. These features are seen in samples of high purity InAs grown by metalorganic chemical vapor deposition on InAs substrates using tertiarybutylarsine and trimethylindium. Only one acceptor species is observed, having a 1 S3/2–2 S3/2 transition energy of 13.39±0.01 meV, and an acceptor–bound exciton binding energy of 2.11±0.03 meV.

Enhancement of high‐temperature photoluminescence in strained Si1−xGex/Si heterostructures by surface passivation

The photoluminescence from strained Si1−xGex alloy quantum wells on Si(100) has been measured from 6 to 300 K. It is shown that the high‐temperature photoluminescence of Si1−xGex quantum wells can be increased by over an order of magnitude by passivation of the top silicon surface. Through experiments and a model, it is clearly demonstrated that the decay of the Si1−xGex photoluminescence at high temperature is controlled by surface recombination, not by an intrinsic property of Si1−xGex. By applying proper conditions, nearly constant Si1−xGex photoluminescence can be achieved from 77 to 250 K.

Characterization of very high purity InAs grown using trimethylindium and tertiarybutylarsine

The growth of high purity InAs by metalorganic chemical vapor deposition is reported using tertiarybutylarsine and trimethylindiμm. Specular surfaces were obtained for bulk 5-10 μm thick InAs growth on GaAs substrates over a wide range of growth conditions by using a two-step growth method involving a low temperature nucleation layer of InAs. Structural characterization was performed using atomic force microscopy and x-ray diffractometry. The transport data are complicated by a competition between bulk conduction and conduction due to a surface accumulation layer with roughly 2–4 × 1012 cm−2 carriers. This is clearly demonstrated by the temperature dependent Hall data. Average Hall mobilities as high as 1.2 x 105 cm2/Vs at 50K are observed in a 10 μm sample grown at 540°C. Field-dependent Hall measurements indicate that the fitted bulk mobility is much higher for this sample, approximately 1.8 × 105 cm2/Vs. Samples grown on InAs substrates were measured using high resolution Fourier transform photoluminescence spectroscopy and reveal new excitonic and impurity band emissions in InAs including acceptor bound exciton “two hole transitions.” Two distinct shallow acceptor species of unknown chemical identity have been observed.

Luminescence in Si/Strained Si 1−x Ge x Heterostructures

This paper quickly reviews the structure of band-edge luminescence in Si/strained Si 1−x Ge x heterostructures, and then focusses on two recent developments -- the origin of “deep” sub-bandgap luminescence which is sometimes observed in structures grown by Molecular Beam Epitaxy (MBE) and the understanding of the temperature dependence of the band-edge luminescence (up to room temperature). Strong evidence will be presented that the origin of the deep luminescence is radiation damage, and that generated defects are segregated or trapped in the SilxGex layers. The modelling of the temperature dependence by twocarrier numerical simulation is presented for the first time. The work and experimental data show convincingly that the strength of the luminescence at high temperature is controlled by recombination at the top silicon surface, which in turn can be controlled by surface passivation. At high pump powers and low temperatures, Auger recombination reduces the lifetime in the Si 1−x Ge x layers, and leads to a luminescence vs. temperature which is flat up to 250 K and which is reduced only by a factor of three at room temperature.

Defect-Free Band-Edge Photoluminescence in SiGeC Strained Layers Grown by Rapid Thermal Chemical Vapor Deposition

The defect-free band-edge photoluminescence at both 30K and 77K was observed for the first time in Si/SiGeC/Si quantum wells. The SiGeC samples were prepared by rapid thermal chemical vapor deposition (RTCVD) by using methylsilane as carbon source added in a dichlorosilane and germane mixture. Deep photoluminescence around 0.8 eV, previously reported by Boucaud et al., was no longer observed under any excitation conditions. Compared to control Si/SiGe/Si quantum wells, the initial effect of adding the C is to decrease the bandgap of the host SiGe layers, despite the fact that the diamond has a large bandgap.