Deep Level Transient Spectroscopy (DLTS) was used to study the defects introduced in Zn and Cd doped Schottky barrier diodes by 2 MeV proton irradiation. The defects H3, H4 and H5 were observed in lightly Zn doped InP, while only the defects H3 and H5 were observed in more heavily Zn doped and Cd doped InP. The defect activation energies and capture cross sections did not vary between the Zn and Cd doped InP.

The concentration of the radiation induced defects was also measured. The introduction rate of the defect H4 in the lightly Zn doped InP and the introduction rate of the defect H3 in the heavily Zn and Cd doped InP were about equal, but the introduction rate of the defect H5 varied strongly among the three types of material. The introduction rate of H5 was highest in the heavily Zn doped InP but the lowest in the heavily Cd doped InP, even though they were doped comparably. As a result, the total defect introduction rate was lowest in the highly Cd doped InP.

The results can be interpreted in terms of the models for the formation and annealing of defects, and by the different diffusion rates of Zn and Cd in InP.

The theory of rare-earth impurities in semiconductors is reviewed. Results of Green's function calculations are presented. The particular case of Ytterbium (Yb) in InP is analyzed in detail. We show that the optical transitions of Yb in InP and their Zeeman splitting can be interpreted by a small coupling between quasi degenerate 5d and 4f states. It also explains the observed lifetimes. This model is coherent with the attribution of the Ec-30 meV level to the Yb3+/Yb2+ acceptor level as proposed recently. We detail the mechanism which allows the energy transfer between a free exciton and the rare-earth impurity. The conditions required for an efficient luminescence are analyzed.

We investigate the influence of Rh-doping on electrical properties of InP and InGaAs. Deep level transient spectroscopy carried out on Rh-doped as well as undoped reference samples reveals a single Rh-related deep level in both semiconductors. While a Rh-related electron trap in InGaAs is situated at EC-0.38eV a Rh-related hole trap is found to exist in InP approximately 0.73 eV above the valence band edge. The internal reference rule for 3d transition metal deep levels is found to be valid for these 4d transition metal levels: their energy is constant across the InGaAs/InP heterojunction. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.

Metastability of defects in semiconductors provides the basis for (1)An integrated picture of defects that includes the DX center in crystalline HI-V compounds, the dangling-bond defect in amorphous Si, and ‘self-compensation’ effects in I1-VI compounds. The unifying physical property is the ability of many foreign atoms to have two nearly equal-energy sites, one with a shallow electronic level and the other with a deep level. (2)Elucidation of stretched-exponential kinetics in these materials, including the first demonstrable microscopic model for them. This stretched-exponential model is a distribution of independent response times.

A comparative study of the effects of hydrogen in n-type (unintentionally and Si-doped) as well as p-type (Mg-doped) MBE-grown GaN is presented. Hydrogenation above 500°C reduces the hole concentration at room temperature in the p-type material by one order of magnitude. Three different microscopic effects of hydrogen are suggested: Passivation of deep defects and of Mg-acceptors due to formation of hydrogen-related complexes and the introduction of a hydrogenrelated donor state 100 meV below the conduction band edge.

We have observed two local vibrational modes related to H bonded to N acceptors in ZnSe samples grown by metal organic vapor phase epitaxy. The modes have been seen in both infrared and Raman spectroscopy. The new mode seen at 3194 cm-1 is assigned to an N-H stretching vibrational mode and the mode found at 783 cm-1 is tentatively assigned to an N-H wagging vibrational mode. Polarized Raman spectroscopy was used to determine that the symmetry of the defect complex is C3v, which implies that the H atom is in either a bonding or anti-bonding position.

Optical admittance spectroscopy is a technique for measuring the conductance and capacitance of a junction under illumination as a function of the wavelength of the light and the frequency of the measuring AC signal. For the first time, this technique is applied to characterize deep defect levels in 6H-SiC:N. Nitrogen is a donor atom in 6H-SiC which substitutes for carbon in three inequivalent sites (h, kl, k2). giving rise to n-type conduction. Deep defect levels attributible to transition metal impurities have been identified in 6H-SiC:N by optical admittance spectroscopy.

Defect concentrations in molecular beam epitaxial (MBE) GaAs range from 1012 to 1020 cm-3 as the growth temperature is lowered from 600 to 200 °C; however, very high quality layers can be grown over this whole range. The dominant defect is the As antisite, but there is also good evidence for As interstitials and gallium vacancies. The particular form of the As antisite center in low—temperature (LT) MBE GaAs is not known at this time, but it is definitely not EL2, because both the thermal activation energy and the electron capture cross section differ significantly. However, other features, such as the EPR spectrum and metastable—to—normal recovery kinetics are identical to those of EL2. The donor (As antisite) to acceptor ratio seems to hold at about one order of magnitude as growth temperature is varied from 200 — 400 °C; thus, the Fermi level stays near mid—gap over this whole range. However, hopping conduction among the As antisite centers is strong for samples grown between 200 and 300 °C and keeps the material from being semi—insulating, while for those grown between 350 — 480 °C, the resistivity is greater than 107 Ω cm. The annealing dynamics are particularly interesting and include such features as the mobility going through a sharp maximum at an annealing temperature of 400 °C for a layer grown at 200 °C. The donor and acceptor concentrations can be determined both by Hall effect and absorption measurements as the layer is annealed up to 600 °C. Above 550 °C, large precipitates are formed. The relative roles of the precipitates and point defects in influencing compensation, lifetime, and device characteristics are a source of much controversy and will be discussed.

The growth of GaAs at low temperatures (LT-GaAs) at or below 250 °C, under standard Molecular Beam Epitaxy (MBE) growth conditions, usually results in a massive incorporation of excess As in the lattice which then totally dominates the electrical and optical characteristics of the as grown material. We report on new phenomena associated with the growth of GaAs at 250 °C and we show, for the first time, data on highly electrically active doped material. By careful control of the growth conditions, namely As4/Ga flux ratios, material in which total defect concentrations of less than 1017 cm-3, well below the huge 1020 cm-3 that is normally obtained in LT-GaAs, can be achieved thereby demonstrating that high quality GaAs can in effect be grown at extremely low temperatures.

Superior electrical and optical quality of GaAs grown on Si with an inserted low-temperature (LT)-GaAs buffer-layer was demonstrated. Photoluminescence intensity was increasing and leakage current of Schottky diodes build on such a structure was decreasing by few orders of magnitude. These observations were correlated with structural studies employing classical and high-resolution transmission electron microscopy (TEM). Bending of the threading dislocations and their interaction was observed at the interface between a cap GaAs layer and the LT-GaAs layer. This dislocation interaction results in the reduction of dislocation density by at least one order of magnitude or more compared for the GaAs layers with the same thickness grown on Si. The surface morphology of the cap GaAs layer is improving as well.

We have investigated the influence of the pressure ratio (PAs4/PGa) on the structural and electrical properties of GaAs layers grown at 250°C by MBE. SEM photographs have revealed smooth surfaces for PAs4/PGa≥15 and Double crystal X-ray rocking curves have shown an increase on the lattice mismatch δaI/a of the L.T. grown layers and high crystalline quality. Resistivity has not been affected by the different values of PAs4/PGa. n-GaAs epilayers grown on top of L.T. buffer layers have their mobility decreased and the electron trap density increased as revealed by Hall and DLTS measurements.

We have studied the near-edge optical response of a LT-grown GaAs sample which was deposited at 300 °C on a Si substrate, and then annealed at 600 °C. The Si was etched away to leave a 3-micron free standing GaAs film. Femtosecond transmission measurements were made using an equal pulse technique at four wavelengths between 825 and 870 nm. For each wavelength we observe both a multipicosecond relaxation time, as well as a shorter relaxation time which is less than 100 femtoseconds.

Compositional modulations and arsenic precipitates in annealed A10.3Ga0.7As layers which were grown at a low substrate temperature (200° C) by molecular beam epitaxy (MBE) were studied by transmission electron microscopy (TEM). These layers were used as surface layer which were applied on metal-insulator-semiconductor (MIS) diode. The planar and cross sectional TEM micrographs reveal that compositional modulations occurred when the thickness of LT AIGaAs was over 1500Å. The wavelength of the modulations varies between 100-200 Å and the direction of the modulation is along \011]. The arsenic precipitates were formed after annealed and the distribution of them followed the compositional modulation. Vertical two dimensional arsenic-precipitates arrays were arranged in the low aluminum constitute region. These novel microstructures result from the strain-induced spinodal decomposition and the arsenic precipitates redistribution process.

The structure and properties of GaAs layers grown by molecular-beam epitaxy at low temperature (150-250 °C) have been studied. The samples were found to contain up to 1.5 at.% extra As, which formed nano-scale clusters under annealing. The dependences of the excessive As concentration and As-cluster size and density on the growth and annealing conditions were established. LT-GaAs layers were found to have high electrical resistivity, however, our investigations of microwave absorption in a weak magnetic field revealed a characteristic signal usually attributed to the superconducting phase. It has been proved that this microwave absorption is unlikely to be due to either the arsenic clusters in LT-GaAs films or indium in the substrate, as it was assumed previously. We suggest a new hypothesis that the superconducting phase in LT-GaAs is Ga nanoclusters formed on the growth surface.

The characterization of III-V compound semiconductor substrates and epitaxial layers with photoluminescence imaging is reviewed. The luminescence patterns of semi-insulating GaAs are dominantly determined by the concentration and distribution of nonradiative recombination centers, as shown by comparison with spectroscopic temperature and lifetime topography of photoexcited carriers. Wafers fabricated with various growth and annealing procedures are evaluated. Presently available informations on nonradiative centers in GaAs are summarized and discussed. The correlation of luminescence, absorption and resistivity topograms of InP substrates shows various interrelated influences of the Fe acceptor distribution. High resolution luminescence images of growth induced, strain induced and substrate induced defects in epitaxial heterostructures are obtained. The generation of relaxation dislocations in pseudomorphic layers is influenced by growth parameters, layer structures, layer doping and also by substrate properties. Nonradiative recombination center patterns replicate the arrangement of threading dislocations in the substrate.

The energy of a general array of dislocations in an epitaxial layer is formulated and expressed in terms of per unit area of interface. Several limiting cases are used to verify the solution and the results are compared to other independent treatments. The critical thickness required for the generation of an isolated dislocation is found by solving for the layer thickness which corresponds to a zero value of the formation energy. The critical dislocation density at a given thickness is also determined. An additional work required for sequential generation of dislocations in an epitaxial layer arises from dislocation-dislocation interaction and has to be expressed in terms of per unit length of dislocation line. The work hardening effect is found to increase sharply with decreasing distance between the fresh and the pre-existing dislocations once the distance falls below approximately twenty times the layer thickness. The additional work achieves the level of the self energy of an isolated dislocation when the distance between the fresh and the nearest pre-existing dislocation is comparable to twice the layer thickness.

Properties of midgap levels in n-type GaAs crystals were studied by using trap density spectroscopy (TDS), capacitance-voltage and near infrared (NIR) absorption measurements. The TDS analysis for various n-type samples showed that the concentrations of the midgap level were from 2.0 × 1016 cm−3 to 3.4 × 1016 cm−3. However, those of EL2 in the same crystals were found to be from 1.1 × 1016 cm−3 to 1.3 × 1016 cm−3 by NIR absorption measurements at room temperature. On the other hand, in undoped semi-insulating GaAs crystals with carbon concentrations ranging from 6 × 1014 cm−3 to 2.4 × 1016 cm−3, the densities of the ionized EL2 determined by NIR absorption were only about 30 % of those of carbon acceptor determined by the localized vibrational mode absorption at room temperature. These differences suggest the presence of another midgap donor which does not give NIR absorption. The concentrations of this trap were estimated to be 0.8 to 1.6 times those of EL2 by decomposition of the TDS spectra into their components.

The well-known 0.15-eV Hall-effect center appearing in bulk, n-type GaAs quenches under IR illumination and recovers via an Auger-like process at a rate similar to the Auger rate of EL2. On the other hand, the 0.15-eV VAs-related center produced by 1-MeV electron irradiation does not quench at all. Based on these data and a detailed theoretical analysis by Baraff and Schluter, we argue that the bulk 0.15-eV center is related to the AsGa-VAs defect or a related complex.

The growth of GaAs epilayers on Si should combine the advantages of both materials. The lattice mismatch and the difference in thermal expansion coefficients, however, result in the yet unsolved problems of high dislocation density and thermal stress in the GaAs layer. Recently, considerable improvements have been achieved by a ‘thermal cyclic growth’ (TCG) process. In this study we focus on the reduction of high defect concentration and dislocation density. The improvement of the epilayer quality is verified by DLTS, PL and DCXD. Results of TEM and DLTS measurements lead to the identification of a dislocation related defect.

Deep Level Transient Spectroscopy (DLTS) is used to investigate the effect of SiC14 Reactive Ion Etching (RIE) on GaAs. At high power (150-80 W) with high DC self bias (380-240 V), five deep levels trapping electrons are observed at energies of 0.30, 0.42, 0.64, 0.86 and ∼0.8 eV below the conduction band edge. Depth profiling reveals an approximate exponential decay of the concentration of the deep levels. At low power the induced concentration falls, the small concentration of remaining deep levels is close to control (no etching) samples. The induced deep levels can account for reduced conductances in n+GaAs wires defined by RIE under similar experimental conditions.