We carry out an investigation of grown-in nonradiative defects in Si and SiGe/Si heterostructures grown by molecular-beam-epitaxy (MBE). A number of such defects are observed by the optical detection of magnetic resonance (ODMR) technique, in samples with various structures and growth conditions. These defects are shown to provide efficient nonradiative shunt paths for carrier recombination, competing with and reducing radiative recombination processes. It is revealed that the dominant nonradiative defect is a low-symmetry vacancy-related complex, evident from a characteristic hyperfine structure due to 29Si ligands (with nuclear spin I=1/2 and natural abundance of 4.67 %) connected to the dangling bonds. The introduction of these defects is believed to be largely due to a low surface adatom mobility during the low temperature growth. By varying the substrate bias during the MBE growth, it is shown that the formation of these nonradiative defects can be effectively enhanced by exposure to accelerated positive ions, presumably dominated by the Si+ ions. Effects of hydrogenation on these defects are also studied.

Stepwise equilibrated graded GexSii-x (x≤0.2) buffers with threading dislocation densities between 102 and 103 cm−2 on the whole area of 4 inch silicon wafers were grown and studied by transmission electron microscopy, defect etching, atomic force microscopy and photoluminescence spectroscopy.

Deep levels in the annealed low-temperature molecular beam epitaxial (LT-MBE) GaAs layer were successfully characterized by using the capacitance deep-level transient spectroscopy (C-DLTS) as well as photocapacitance quenching technique in combination with a unique sample structure. In this work, we have fabricated the samples by inserting the LT-GaAs layer into two n-type semi-conductive layers, like a sandwich (n-LT-n structure), grown at normal substrate temperatures. DLTS measurements have revealed that one electron trap dominates the annealed LT-MBE GaAs. The dominant electron trap was very similar to the so-called EL3 level. Moreover, we found the midgap level appeared upon 800-900°C RTA, although no midgap level was detected in the as-grown n-LT-n sample (annealed at 620°C) and confirmed with photoquenching measurements that it is the EL2 level.

A study was carried out to characterize the deep impurities in AlxGa1-x As grown by metal-organic chemical vapor deposition (MOCVD) using different carrier gases. Since AlxGai1-x As is very sensitive to any impurities, especially moisture and oxygen, in the growth process, the concentration of impurities in AlxGai1-xAs can serve as a measure of the purity of carrier gases. The undoped AlGaAs layers grown by using H2 have n-type background concentrations from 3×1015 to 10×1015/cc. The concentrations of oxygen-related traps (Ec−0.53 and 0.7 eV) are 0.2−9×1013 and 3.4−5×1014/cc for Pd- and Li-purified H2, respectively. Low-temperature photoluminescence (PL) measurements show better PL efficiency in samples grown by using Pd- purified H2. AlxGa1-xAs grown by using N2 is p-type (p∼6×1016/cc) with an oxygen-related trap and two hole traps. The concentration of oxygen-related trap is more than one order of magnitude higher than that of AlGaAs using Pd-purified H2. The memory effect due to impurities from carrier gas left in source materials is also studied.

GaAs epilayers doped with dimethylaluminum methoxide (DMA1MO), an alkoxide bearing a pre-formed Al-O molecule, have been investigated using local vibrational mode (LVM) absorption and deep level transient spectroscopy measurements. LVM measurements indicated that oxygen and aluminum atoms are incorporated into GaAs layer as a complex and remain bound in the volume of the crystal. Electron traps with activation energies of 0.74 and 0.93 eV below the conduction band are main deep level defects responsible for the electrical and optical properties of the layers. Interpretation of the relationship between trap concentration and growth conditions led to the conclusion that the 0.93 and 0.74 eV traps have the atomic structures in which oxygen atom is bonded to one (AlO) and two aluminum atoms (A12O), respectively.

Intentional defect incorporation in metalorganic vapor phase epitaxy (MOVPE) InxGai-xAs was achieved by controlled oxygen doping using diethylaluminum ethoxide (DEALO). DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in InxGai-xAs:Si with 0≤x≤ 0.25. DLTS analysis on a series of InxGa1-xAs:Si:O samples with 0≤x≤ 0.18 showed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. The characteristic deep levels appear to remain at a relatively constant energy with respect to the valence band.

The presence of point defects is expected to influence the properties of free carrier in semiconductors. We have used the techniques of ultrafast laser spectroscopy to characterize the dynamics of photoinjected carriers in several III–V semiconductors grown at low temperature. The initial scattering time and the lifetime of the carriers become very short at low growth temperatures. Results obtained with low-temperature grown III–Vs are compared to those obtained with III–Vs grown at normal temperatures and amorphous silicon.

A series of carbon delta- and uniformly- doped GaAs and Al0.3Ga0.7As films have been grown by solid source Molecular Beam Epitaxy using an electron-beam heated graphite rod as the dopant source. In contrast to heated filament carbon sources, this electron-beam source produces atomic carbon C1, rather than C3 as the predominant species. The purpose of these experiments was to compare measured sheet carrier concentration of delta-doped GaAs and Al0.3Ga0.7As films under fixed growth conditions and with similar carbon beam fluxes using this electron-beam source. The films were characterized by Hall-effect measurements. The Al0.3Ga0.7As films have consistently higher hole sheet carrier concentrations than GaAs films with similar carbon fluxes. Delta-doped Al0.3Ga0.7 As sheet carrier concentrations of up to 2.2×1013 cm−2 were measured, and thin uniformly-doped Al0.3Ga0.7 As carrier densities were measured up to 5.7×1020 cm−3. The uniformly doped Al0.3Ga0.7As films appear to have higher atomic carbon activation than this delta-doped Al0.3Ga0.7As films. These results can be possibly explained in terms of several concurrent processes involving C-C pairing, stronger Al-C bonding, and dopant surface segregation taking place on the growth surface of the delta-doped layer. Photoluminescence intensity measurements of uniformly-doped GaAs shows degradation at hole concentrations greater then 1018 cm−3 and bandgap contraction at hole densities greater than mid 1018 cm−3.

Formation of defects during Zn diffusion into undoped and Fe-doped InP single crystals at 700°C has been observed by transmission electron microscopy for various diffusion conditions. The observations are correlated with Zn concentration profiles obtained by electron microprobe measurements and secondary-ion mass spectrometry. The results allow the conclusion that indiffusing interstitial Zn can occupy In sublattice sites via a kick-out reaction. Under appropriate diffusion conditions supersaturations of In self-interstitial atoms result leading to defect formation. Observations in Fe-doped InP suggest that Zn also replaces Fe on In sublattice sites leading to redistribution and to precipitation of Fe.

InxGai-xP (x=0.49) layers lattice-matched to GaAs have been grown by metalorganic chemical vapor deposition (MOCVD). We did not observe any deep levels in the temperature range of 30-380K by deep level transient spectroscopy (DLTS) in undoped In0.49Ga0.51P layers which have a background concentration of 3.1×1015 cm−3. The deep levels, if they exist, have a concentration of less than 5×1011 cm−3, which is the lowest deep level concentration found so far in InxGa1-xP materials. Moreover, lattice-mismatched InxGa1-xP/GaAs heterojunctions were deliberately grown by varying the In-composition ranging from 0.43 to 0.57. No deep levels were created in 1-μm-thick InxGa1-xP layers due to lattice mismatch when 0.469 < x < 0.532. However, we have observed a shallow electron trap at EC - 60 meV in InxGa1-xP layers with x < 469, and a deep electron trap located at Ec - 0.85 eV in the samples with x > 0.532. We suggest that the lattice-mismatch-induced-defects in InxGa1-xP are either electrically inactive or resided outside the bandgap when In content ranging from 0.469 to 0.532.

We have achieved deep-level-free Al0.22Ga0.78As epitaxial layers using low selenium (Se)-doping (8.4 × l016 cm−3) grown by metalorganic chemical vapor deposition (MOCVD). Deep levels in various Al0.22Ga0.78As layers grown on GaAs substrates were measured by deep level transient spectroscopy (DLTS). We have found that the commonly observed oxygen contamination-related deep levels at EC-0.53 and 0.70 eV and germanium-related level at EC-0.30 eV in MOCVD-grown Al0.22Ga0.78 As can be eliminated by low Se-doping. In addition, a deep hole level located at Ev+0.65 eV was found for the first time in highly Se-doped Al0.22Ga0.78 As epilayers. We suggest that low Se-doping (<2 × 1017 cm−3) produces a passivation effect and then deactivates other deep levels in Al0.22Ga0.78As.

Non-stoichiometric GaAs layers with semi-insulating properties can be produced by low-temperature molecular beam epitaxy or ion implantation. The latter is the subject of the present report wherein the solid-phase epitaxial growth of amorphized, non-stoichiometric GaAs layers has been investigated with time-resolved reflectivity, Rutherford backscattering spectrometry and transmission electron microscopy. GaAs substrates were implanted with Ga and/or As ions and annealed in air at a temperature of 260°C. The recrystallized material was composed of a thin, crystalline layer bordered by a thick, twinned layer. Non-stoichiometry results in a roughening of the amorphous/crystalline interface and the transformation from planar to non-planar regrowth. The onset of the transformation and the rate thereof can increase with an increase in non-stoichiometry. Non-stoichiometry can be achieved on a macroscopic scale via Ga or As implants or on a microscopic scale via Ga and As implants. The influence of the latter is greatest at low doses whilst the former dominates at high doses.

We study magnetic circular dichroism of absorption (MCDA) of LT AlxGa1−xAs as a function of aluminum content. The MCDA spectrum of LT AlxGa1−xAs is distinctly different from the MCDA spectrum of LT GaAs, which has one paramagnetic and one diamagnetic peak at 0.95 eV and 1.18 eV, respectively. As the aluminum content increases, the spectrum of LT AlxGa1−xAs is dominated by a diamagnetic peak similar to the 1.18eV peak of the EL20-like defects in LT GaAs. However, the peak shifts to higher energies as x increases. The photoquenching and temperature dependence of this peak indicates an association with the EL2 defect. The paramagnetic peak observed in LT GaAs also shifts to higher energies but faster and eventually merges with the diamagnetic peak as the Al content increases. The study of the MCDA spectrum of LT AlxGa1−xAs as a function of aluminum content allows a better understanding of the MCDA phenomena of LT AlxGa1−xAs and LT GaAs, as well as the EL2-related transitions in bulk semi-insulating GaAs.

Pseudodielectric functions of low temperature grown GaAs (LT GaAs) measured by spectroscopic ellipsometry are presented. The spectral range includes the El (2.92eV) and El+ΔAl (3.13eV) critical point structure of GaAs. A Lorentz-oscillator model was used to fit the dielectric function of LT GaAs for samples with nominal growth temperatures (Tg) varying from 200°C to 580°C. For Tg of 200°C, 30% and 19% broadenings and −0.01 leV and −0.007eV red shifts were found for the El and El+Δl structures respectively, compared with normal GaAs. The red shift can be explained in terms of a strain effect in the LT layer. In annealed LT GaAs the broadening decreased significantly and no red shift was found.

The optical absorptions and the defect densities of GaAs grown by low temperature molecular-beam-epitaxy at growth temperatures between 200-580 °C were evaluated by photothermal deflection spectroscopy. The shapes of the absorption spectra exhibit EL2-like characteristics. Defect densities were found to be in the range of 1018-1019 cm−3. The PDS phase spectra were shown to be useful to differentiate the absorptions of the epilayer from those of the bulk.

The transition energy, the binding energy, the intensity, the broadening and the lifetime of the free-exciton transitions in GaAs epitaxial layer have well been investigated using photoconductivity measurement which is analyzed in term of an improved fitting model. We have found that as the thickness is increased, the bind energy increases, but both the intensity of the high excitonic level and the lifetime of the excitons decrease. These effects are attributed mainly to imperfections located near the surface of the epitaxial layer.

We have studied the uniformity of the arsenic flux from a commercially available valved arsenic cracker source for MBE. There are many epitaxial structures that require a uniform arsenic flux distribution for rotated epitaxial growth and, in the non-rotated case, for RHEED. For non-stoichiometric GaAs growth at low substrate temperatures, which results in arsenic precipitates being formed during the in-situ anneal process, a specific As/Ga ratio must be used to maintain high crystalline quality and to achieve the desired electrical properties. Also, in the growth of InGaAsP the As/P ratio is equally important for lattice match and quality device results. We report on the uniformity of amorphous arsenic (a-As) films condensed on the surface of 3" diameter sapphire wafers slightly below room temperature. Sapphire substrates were used in place of GaAs wafers to facilitate the use of x-ray fluorescence for the measurement of the arsenic film uniformity. Uniformity maps will be presented for rotated and non-rotated a-As depositions of As2 and As4. Results indicate the uniformity of a-As, As4, films to have a standard deviation of < 2.5% across a 3" diameter substrate for the rotated case. Characteristics of the non-rotated case will be presented.

The application of the perturbed γγ angular correlation technique (PAC) as an analytical tool for the characterisation of atomic defect configurations is discussed, using recent results on donor-acceptor pairs, which were observed in CdTe and other II-VI semiconductors by the radioactive donor 111In. For bulk CdTe crystals and MOCVD grown CdTe films, the role of the cation vacancy, group I and group V elements is discussed.

Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/Cu2Se heterojunction interface. Cu2−xSe layers were deposited on GaAs (100) by molecular beam epitaxy from Cu2Se sources. Raman spectra reveal a strong peak at 270 cm−1, indicative of the Cu2−xSe phase. Atomic force microscopy reveals uniaxial growth in a preferred (100) orientation. CdS overlayers were then deposited in-situ, at room temperature, in steps on these epilayers. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Se3d and Cd4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the CdS/Cu2−xSe and heterojunction valence band discontinuity and the consequent heterojunction band diagram. These results are compared to the valence band offset (ΔEv) for the CdS/CuInSe2 heterojunction interface.

The mono- and polycrystalline films of the SnTe1+x semiconducting phase with controlled content of nonstoichiometric defects (NSD) were grown by thermal evaporation and hot wall epitaxy methods from the charges of different composition. The concentration of NSD was determined using X-Ray diffraction method and the measurements of carrier density. The temperature dependences of electrical conductivity and Hall coefficient were obtained in the temperature range of 77 - 300 K. The best results were obtained for hot wall epitaxy method: the perfect monocrystalline films with NSD content corresponding to x =0-0,025 and high mobility of charge carriers were grown.