In this work we study effects of growth temperature and use of surfactant during growth on thermal quenching of photoluminescence (PL) from SiGe/Si quantum wells (QWs) grown by molecular beam epitaxy (MBE). We show that although all investigated structures demonstrate intense and sharp excitonic emissions from the SiGe QWs at liquid helium temperature, thermal quenching of this PL critically depends on the growth conditions. In particular, the use of low (⁤ 550°C) growth temperatures or employing Sb as a surfactant during high temperature (620°C) growth considerably degrades the PL thermal quenching behaviour by introducing some competing quenching processes with low activation energies of about 5 meV. The optimum growth conditions judging from the PL thermal behaviour are realised during high temperature growth without surfactant (620°C). Even higher growth temperature is shown to be required during surfactant mediated growth to improve the thermal quenching behaviour. From optically detected magnetic resonance (ODMR) studies, the competing quenching processes are attributed to a thermal activation of non-radiative defects introduced during either low-temperature MBE growth or during surfactant-mediated growth.

We discuss a new method for plasma enhanced chemical vapor deposition, applied to the epitaxial growth of Si and of Si-Ge heterostructures. Growth rates up to 5 nm/s become possible at substrate temperatures below 600°C, by utilizing very intense but low energy plasmas to crack the reactive gases, SiH4 and GeH4, and to speed up the surface kinetics. The method is applied to the synthesis of step-graded Si-Ge buffer layers, exhibiting the well known cross-hatched surface morphology.

The growth by rapid thermal chemical vapour deposition of Si/Si1-xGex/Si multilayer structures, suitable for thin bond and etch-back silicon-on-insulator fabrication has been investigated. Surface topography was studied by scanning probe microscopy, and layer contamination by secondary ion mass spectrometry. Smooth layers are only achieved at high growth temperatures (>700°C), and when surface oxide contamination is reduced by a combination of ex-situ HF vapour treatment and in-situ high temperature H2 bake. A surface peak-to-peak roughness of 15nm for a Si/Si1-xGex/Si multilayer structure has been achieved by reducing the growth time at 700°C or less. Further improvement is possible, especially if carbon contamination can be reduced.

Selective Epitaxial Growth (SEG) of Si and SiGe suffers from pattern sensitivity. The growth rate and layer composition change with the pattern and the window size. In relation to growth at atmospheric pressure, the sensitivity to the window size is suppressed at reduced pressure, whereas some growth rate effects of a more global nature become more visible. The Si growth rate decreases when the area of exposed silicon on the wafer and the susceptor decreases. SiGe shows the opposite behavior: its growth rate increases with decreasing silicon area. Another difference between Si and SiGe is the range over which the loading effects are active. The influence of a large silicon area on the Si growth rate can be felt inches away, whereas the SiGe growth rate is affected over a much shorter distance. In common epi reactors the wafer rests on a susceptor, which extends beyond the wafer, exposing a large Si-coated surface area around the circumference of the wafer. Consequently, the Si growth rate varies unacceptably across the wafer. A sacrificial polysilicon layer has been successfully applied to improve the growth rate uniformity across the wafer.

A selective/non-selective epitaxy process for a novel self-aligned SiGe HBT structure is described. It is shown that damage in the silicon substrate induced by reactive ion etching can be effectively removed and that this allows the growth of high quality selective and nonselective epitaxy. Control of the base thickness and doping can be maintained during selective and non-selective epitaxy, thereby demonstrating the feasability of producing the self-aligned HBT structure.

Photoluminescence (PL) of SiSnC alloys grown on Si (100) substrate by molecular beam epitaxy (MBE) has been investigated. The following epitaxial layers were investigated. The samples were similar in structure, and consisted of a 200 Å Si buffer layer grown on a (100) Si substrate followed by the respective alloy layer; a 4500 Å Si0.955Sn0.03C0.015, a 1500 Å Si0.9Sn0.04, or a 1500 Å Si0.985C0.015. The layer composition was measured by Rutherford back scattering spectrometry (RBS) and confirmed by x-ray diffraction analysis (XRD). X-ray diffraction measurements of the layers confirmed the Sn and C were substitutional and the layers were pseudomorphic and coherently strained. The Si0.955Sn0.03C0.015 alloy layer was found to be strain compensated. PL spectra of all the layers revealed band edge luminescence as well as a very sharp peak at 0.767 eV superimposed on a very broad peak that exhibited excitonic behavior. The addition of C to the alloys resulted in a reduction of the bandgap, contrary to what is predicted by Vegard's Law. However, the addition of Sn results in a reduction in the bandgap, which was attributed to the bulk alloy effect and residual strain. The luminescence feature at 0.767 eV was found to be much more intense in alloys that contain carbon. We have observed quite similar deep-level well resolved PL spectra for SiGe, SiC, SiSn, SiGeC, SiSnC, and SiGeSnC alloy layers grown by MBE on Si (100) substrates. Previous studies on PL of silicon have reported a peak at 0.767 eV to be associated with oxygen (P line) and the broad peak to carbon/oxygen complexes.

Layer-by-layer hetero-epitaxy of Ge has been successfully demonstrated on the Si(100) surface by combining the initial IML-Ge film growth on the Si surface and the successive Ge atomic-layer-epitxy (ALE), for the first time. The former was achieved using the substrate temperature modulation with alternate exposures of GeCL4 and atomic H, and the later was established by cyclic exposures of (CH 3)2GeH2 and atomic H under isothermal conditions. XPS measurements confirmed a discrete and uniform increase in the grown Ge film thickness with one monolayer/cycle step up to the critical Ge thickness, and no C contamination at the Ge/Si interface. Critical exposure for the saturated Ge adsorption was different from that for the homo-ALE on the bulk Ge surface.

A short discussion about growth kinetics of Si and Si1-xGex, epitaxial layers in a reduced pressure CVD reactor using both dichlorosilane and silane is presented. Through careful observations of the growth of very thin Si layers on SiGe, an anomaly in the Si growth ratewas detected such that the thinner the Si layer, the higher the Si growth rate on SiGe. Due to the difficult nature of very thin film characterization, several analysis techniques were used. A possible explanation based on TEM observations is put forward.

Single and double Si1-xGexx/Si quantum well (QW) structures, which were grown by atmospheric pressure chemical vapor deposition (APCVD), are characterized by photoluminescence and secondary ion mass spectrometry. Systematic post-growth annealing treatments were carried out at temperatures between 600°C and 1100°C in pure N2 ambient. The interdiffusion between the Si layer and the Si1-xGex, well layers occurs at the annealing temperature around 900°C. The diffusion coefficient is deduced at different temperatures from SIMS measurements for single QW structures. The activation energy is about 3.9 eV in the temperature range between 950°C and 1100°C. The double QW structures show a similar value, but the accurate value is more difficult to obtain because it is more complicated to analyze the SIMS profile of the double QW structures. The intensity of the exciton recombination related to carriers confined in the double QW structures decreases with increasing annealing temperatures and becomes strongly suppressed at 750°C. When the annealing temperature is increased further, the intensity of the QW emission recovers. The results indicate that nonradiative centers were generated at annealing temperature of about 750°C

In-situ heavy doping of B into Si1-xGex epitaxial films on the Si(100) substrate have been investigated at 550°C in a SiH4(6.0Pa)-GeH4(0.1−6.0Pa)-B2H6(1.25 ×10−5−3.75 × 10−2Pa)-H2(17–24Pa) gas mixture by using an ultraclean hot-wall low-pressure CVD system. The deposition rate increased with increasing GeH4 partial pressure, and it decreased with increasing B2H6 partial pressure only at the higher GeH4 partial pressure. As the B2H6 partial pressure increased, the Ge fraction scarcely changed although the lattice constant of the film decreased. These characteristics can be explained by the suppression of both the SiH4 and GeH4 adsorption/reactions in a similar degree due to B2H6 adsorption on the Si-Ge and/or Ge-Ge bond sites. The B concentration in the film increased proportionally up to 1022cm3 with increasing B2H6 partial pressure.

Growth and structural characterization of ultrathin, coherently strained oc-Sn/Si quantum well heterostructures have been performed. Severe Sn segregation to the surface during growth, which prevents growth of these structures at ordinary Si epitaxy temperatures, has been minimized by substrate temperature and growth rate modulations during molecular beam epitaxy. Single Sn/Si quantum wells grown with Sn coverage up to 1.4 ML have been verified to be pseudomorphic by transmission electron microscopy and X-ray rocking curve analysis. Similarly, pseudomorphic superlattices with up to 10 periods of 1 ML Sn/7.7 nm Si have been verified to be free of extended defects.

We report on the epitaxial growth of Ge-C and Ge-Si-C alloys (C<10%) grown on Si(100) and Ge(100) substrates using low temperature (∼200°C) molecular beam epitaxy. Thin films (50–70 nm) were characterized in-situ by RHEED and ex-situ by transmission electron microscopy, xray diffraction, and Raman spectroscopy. The films were annealed at 750°C and 850°C in an Ar atmosphere to study interdiffusion effects.

Raman spectroscopy of Ge-C on Ge indicates the existence of a Ge-C local mode at 530cm−1 and is direct evidence for the presence of substitutional C in Ge. The GeSiC alloys grown on Ge do not show the Ge-C local mode, consistent with preferential Si-C bonding. There is evidence for strain enhanced solubility of C based on a comparison of the substitutional C content in Ge-C films on Si (∼1 at %) and on Ge substrates (∼0.1 at %). Silicon interdiffusion in annealed Ge-C samples is strongly suppressed by the presence of C. A simple diffusion model is used to illustrate Si indiffusion in Ge.

Previously, atomic hydrogen has been shown to be effective in reducing the segregation of Sb on Si(100) during solid source molecular beam epitaxy growth. In this work we have investigated the electrical activation of the Sb. Using Hall measurements, spreading resistance profilometry, and secondary ion mass spectrometry, we have demonstrated that the co-deposition of atomic hydrogen during Sb doping of Si at 500°C produced well-defined doping spikes. Comparing the sheet carrier concentration obtained by Hall measurements to the Sb atomic concentration obtained by SIMS, the overall activation of the Sb was greater than 50%.