Broad photoluminescence (PL) bands with energy position ranging from 0.70 to 1.03 eV, are shown to appear in Si epilayers and Sil−xGex/Si heterostructures grown by molecular beam epitaxy under non-optimized conditions. The presence of a particular broad band (BB) is found to be determined by the growth conditions, in particular by the bias applied to the substrate during the growth. Ion bombardment during the growth is shown to be a main factor enhancing the formation of BB-related defects. To clarify their origin, the effects of post-growth hydrogen treatments and of an external magnetic field are investigated. The BBs are shown to be related to various types of radiative centres, either point or extended defects. A correlation between X-ray diffraction and PL measurements is also observed. The spatial location of the BB-related defects is inferred by results from optically detected cyclotron resonance (ODCR) and PL excitation studies.

Donor-doping in silicon molecular beam epitaxy (MBE) is still an open problem, due to the low solid solubility and the strong segregation behavior (Sb, As) or to the high vapor pressure of the doping elements (P, As). Based on its high solubility elemental P2 would be the best candidate for heavy n-type doping. A new developed phosphorus source, based on the decomposition of solid GaP with a simultaneously mass separation of the parasitic Ga atoms has been applied. Homogenous P-doping higher than 1019 cm3 in Si and strained SiGe has been achieved. No surface accumulation of phosphorus was observed. The parasitic Ga incorporation is about three orders of magnitude below the P concentration. In this paper we will demonstrate the use of such cell to incorporate electrical active phosphorus during MBE growth. The incorporation probabilities into Si and strained SiGe will be compared. The dependence of segregation-/diffusion processes of phosphorus on growth temperature during the MBE will be shown. SIMS investigations on undoped Si layers reveal no P or Ga “memory effect” of the UHV equipment.

Heterostructure devices composed of silicon, silicon-germanium or germanium layers have substantially broadened the spectrum of the well established Si microelectronics. The achieved results for devices, such as the SiGe base heterobipolar transistor (SiGe HBT), the n-. and p-channel SiGe modulation doped field effect transistor (SiGe MODFET) and optoelectronic devices (SiGe LED and photodiode) point to the outstanding potential of this novel heterosystem. Today the SiGe HBT is the world fastest Si based transistor with a wide application area from conventional microelectronic applications to microwave power generation in a frequency regime where up to now only III-V semiconductor devices have prevailed. In addition novel SiGe optoelectronic devices, such as SiGe LED and Si/Ge photodetector in the near infrared spectral region (1.3µ) could pave the way for Si based optical interconnect devices monolithically integrated on a Si IC chip (chip to chip coupling). Growth aspects, strain effects, band alignment and novel bandstructure effects in this material system will be reviewed, its effect on the device performance will be discussed.

Dislocation-free Si1−xGex epilayers are successfully grown on (100) silicon at 440°C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD). The effects of process parameters on the crystallinity of Si1−xGex epitaxial layers were studied. As the GeH4 flow rate increases and consequently Ge fraction increases above 20%, Si1−xGex epilayers become damaged heavily by ions. When Ge fraction is larger than 20%, process parameters like total pressure need to be adjusted to reduce the ion flux for high quality Sil−xGex. Growth rate of Si1−xGex epitaxial layers increases at 440°C with Ge content in the film. It is presumed that the hydrogen desorption from the surface is the rate-limiting step, however, the enhancement in growth rate is comparatively suppressed and delayed.

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.

We have investigated structural and optical properties of SiGeC layers. Bulk and multiquantum wells heterostructures were grown by rapid thermal chemical vapor deposition. The photoluminescence of these structures exhibits two distinct features : deep level photoluminescence associated with localized states and bandedge photoluminescence which gives an indication of the band gap variation due to carbon incorporation in substitutional sites. In the case of multiquantum wells heterostructures, a strong segregation is reported as the growth temperature is decreased. An alternate technique to incorporate carbon in SiGe layers, the pulsed laser induced epitaxy with an excimer laser, is presented. The incorporation of carbon in substitutional sites is evidenced by Raman spectroscopy. As the laser flux is increased, new Raman lines associated to carbon-induced disorder are observed in the spectra.

Transmission electron microscopy has been combined with time-resolved reflectivity and ion channeling to study the effects of regrowth temperature and carbon introduction by ion implantation on the solid phase epitaxial regrowth (SPER) of strained 2000Å, Sio.88Ge0.12/Si alloy films grown by molecular-beam epitaxy (MBE). Relative to the undoped layers, carbon incorporation in the MBE grown SiGe layers prior to regrowth at moderate temperatures (500- 700°C) has three main effects on SPER; these include a reduction in SPER rate, a delay in the onset of strain-relieving defect formation, and a sharpening of the amorphous-crystalline (a/c) interface, i.e., promotion of a two-dimensional (planar) growth front.1 Recrystallization of amorphized SiGe layers at higher temperatures (1 100°C) substantially modifies the defect structure in samples both with and without carbon. At these elevated temperatures threading dislocations extend completely to the Si/SiGe interface. Stacking faults are eliminated in the high temperature regrowth, and the threading dislocation density is slightly higher with carbon implantation.

Strained layer Si/Si0.79Ge0.21 superlattices consisting of 16 alternating 19.0 nm Si0.79Ge0.21 / 18.5 nm Si layers have been amorphized by Si ion irradiation, then implanted with H ions to nominal atomic concentrations of 1%, 0.1% and 0.05% within the amorphized region. Subsequent solid phase epitaxy (SPE) at a regrowth temperature of 575°C was monitored in situ by time resolved reflectivity (TRR) measurements, while changes in the H distribution were measured by elastic recoil detection analysis (ERDA). Analysis was supplemented by Rutherford backscattering spectrometry (RBS), x-ray double crystal diffraction and reflectivity (DCD/XRF) and transmission electron microscopy (TEM). TRR data reveals a decrease in the initial SPE rate in the Si substrate from 4.9 Å/sec (no H) to 2Å/sec for 1% H concentration as well as a rate decrease as the interface enters the Si/SiGe layers. TRR also indicates an increased roughness in the crystal/amorphous interface with increasing H concentration. ERDA reveals that a significant fraction of the implanted H is stable in the amorphous region for the anneal times (10-30 min) at 575°C, while in the regrown lattice the H concentration has dropped below 20 ppm, near the detection limit of the ERDA. DCD shows almost no strain in the regrown structures. TEM and RBS channeling techniques reveal degradation in the crystal quality of epitaxially regrown structures and a large concentration of strain relieving defects originating near the second deepest of eight SiGe layers in all regrown structures. XRF indicates decreasing sharpness of the regrown Si/SiGe interfaces with increasing H concentration.

Metastable pseudomorphic GexSi1−x (x=8%,16%) films were deposited on p-Si(100) substrates by chemical-vapor-deposition and then implanted at room temperature with 90 keV arsenic ions to a dose of 1.5×1015/cm2. The implantation amorphizes approximately the top 125 nm of the 145 nm-thick GeSi layers. The Si-GeSi interfaces remain sharp after implantation. Implanted and non-implanted GeSi samples, together with implanted Si control samples, were subsequently annealed simultaneously by rapid thermal annealing in a nitrogen ambient at 600,700,800 × for 10,20,40s at each temperature. The implanted samples undergo layer-by-layer solid-phase epitaxial regrowth during annealing at or above 600 ×C. The amorphized and regrown GeSi layers are always fully relaxed with a very high density of dislocations (1010-1011/cm2). At a fixed annealing temperature, strain relaxation of an implanted GeSi film is substantially more extensive than that of a non-implanted one. About 50-90% of the implanted arsenic ions become electrically active after the completion of solid-phase epitaxy. The percentages of arsenic ions that are activated in the Si control samples are generally higher than those in GeSi. The room-temperature sheet electron mobility in GeSi is roughly 30% lower than that in Si for a given sheet electron concentration. We conclude that metastable GeSi on Si(100) amorphized by arsenic ions and recrystallized by solid-phase epitaxy cannot recover both its crystallinity and its pseudomorphic strain under rapid thermal annealing.

We review growth and optical properties of strain balanced, InGaAs/GaAsP Multiple Quantum Well structures on GaAs in order to make defect free, 1.06 µm modulators. Here, we implement strain balancing near the elastic limit on a length scale of strong size quantization so as to open up a special class of semiconductors materials. In this system we find the in-plane electron mass is strain-enhanced by 30 %. This preserves both excitonic binding energy and excitonic oscillator strength. Consequently, quantum well absorption at 1.06 pan can be nearly comparable to that of a GaAs qw. Also, strain balanced materials show an improved capacity over 850 nm MQW to optically modulate light signals through the Quantum Confined Stark Effect. This is attributed to a light -heavy hole splitting of 140 meV that is caused by a large component of shear strain in these systems. Growth of strain balanced materials is challenging because the strain energy can be comparable to the surface energy that bonds atoms to the crystal. In order to accurately predict the critical layer thicknesses for strain relief as well as the reorganized surface topology, we develop a 2D-3D growth mode model.

Short-period (InAs)6/(AlSb)6 superlattices (SL) with AlAs-like and InSb-like interfaces (IF) grown on a relaxed AlSb buffer layer are studied by X-ray reflectivity and diffractometry measurements. Reflectivity measurements reveal average IF roughnesses between 0.6 and 1.0 nm. Measurements of the diffuse scattering show that the roughness is highly correlated from layer to layer. Triple crystal area scans illustrate that the inhomogeneous deformation of the buffer layer leads to a certain symmetric peak broadening. In the case of AlAs-like IFs an additional broadening of the SL peaks reveals lattice parameter gradients over the superlattice. This asymmetric peak broadening may be attributed to a further relaxation of the superlattice, which is inhomogeneous with depth. The diffusion of As into the AlSb layers leads to a peak shift and modifies the intensity ratios of the different satellite reflections. The best structural quality is achieved for superlattices with InSb-like IFs.

The compositional abruptness at both the normal and the inverted InGaAs/Ga(Al)As interface is inherently limited by the surface segregation of In atoms during molecular beam epitaxy. We find, for example, that the intended alloy composition in In0.22Ga0.78As layers is not reached until nearly 35 Å from the normal InGaAs on GaAs interface for growth at 500 °C. We propose and demonstrate a scheme to control and eliminate the compositionally graded region at the normal interface by the artificial formation of an In surface segregated layer (predeposition) prior to the growth of InGaAs.

The dynamics of In surface segregation during molecular beam epitaxy growth of In.22Ga.78As/GaAs quantum wells (QWs) are studied by temperature-programmed desorption (TPD). The TPD spectra show two In peaks: a low temperature (low-T5) peak and a high temperature (high-T5) peak, which arise from desorption of surface segregated In and dissociation of the underlying InGaAs lattice, respectively. Integration of the low-Ts peak provides quantitative determination of the surface segregated In population ΘIn, as a function of InGaAs layer thickness, incident arsenic dimer flux [(Fi(As2)], InGaAs growth temperature, and GaAs cap thickness. The surface segregated In population ΘIn, is observed to grow with InGaAs thickness, until reaching a temperature-dependent steady state value between 1.0 and 2.0 monolayers after approximately ten monolayers of growth, and then decays during GaAs overlayer growth. The variation of ΘIn with thickness closely mimics the resulting vertical composition profile, which is characterized by an In-depleted bottom interface and segregation of In into the GaAs cap. Based on these results, a sequence of: 1) In predeposition, 2) InGaAs growth, and 3) thermal desorption of Eh is proposed to produce a more square InGaAs/GaAs QW than can be obtained by more standard MBE approaches.

InxTll−xP has been proposed as a potential narrow bandgap material for the fabrication of IR detectors. 1 It is expected to exist in a zincblende structure with a lattice constant approximately 2% larger than aInP for x=0. In this paper we will discuss attempts to grow this alloy on InP using various combinations of elemental and gaseous sources including In, Tl, trimethylindium (TMI), triethylindium (TEI) and phosphine. The sticking coefficient of Tl was found to decrease rapidly for temperatures above 350°C, mandating the use of low temperatures. Attempts to grow TIP resulted in the formation of Tl droplets which oxidized rapidly upon removal from the vacuum system. Auger analysis of the surface shows the oxide composition to be Tl2O, indicative of a monovalent Tl oxidation state. InTlP grown under similar conditions shows an initial tendency to form structural defects, as observed by cross-sectional TEM, suggesting lattice mismatch due to incorporation of small amounts of Tl. As the Tl concentration at the growth surface is increased, a two-phase material is obtained consisting of Tl-rich droplets and InP. In addition, Auger depth profiling shows clear evidence of Tl segregation.