We have performed studies on Vanadium doped InP, especially p-type InP codoped with Zn and V. Luminescence excitation experiments, DLTS, DLOS and absorption experiments lead to the conclusion that the donor level (V3+/V4+) of Vanadium is at about 0.2 eV above the valence band. Optical cross-sections that are determined by DLOS allow to observe for the first time a resonance in the valence band of a III-V semiconductor that we tentatively interpret as an excited state of V4+.

We report the results of a low temperature photoluminescence study of Cd related centers in InP. Besides the previously identified 1.365 eV band a new Cd related band is reported. The peak position of this band lies in the energy ranqe 1.2-1.3 eV at 5.5K dependinq upon the excitation intensity. The peak position of the bands shifts to higher energy with increasing excitation intensity but the change in the peak energy per decade chanqe in excitation intensity is much larger (50 meV) for the lower energy band compared to the 1-2 meV shift for the 1.365 eV band. Both bands exhibit thermal quenching of luminescence above lOOK with an activation energy of 54±4 meV which is comparable to the ionization energy for the substitutional Cd acceptor, CdIn. From this we infer that both bands involve the CdIn acceptor in the recombination process. While the excitation dependence of the bands suggests a donor-to-acceptor pair recombinaton for their origin, we present arguments to show that the larger shift of the peak energy of the 1.2-1.3 eV band with excitation intensity is perhaps a consequence of the involvement of a deep donor in its origin as opposed to a shallow donor in the 1.365 eV band. It is suggested that the deep donor is related to Cd and possible centers are discussed.

We have analyzed the photoionization of Cr2+ in InP by the Deep Level Optical Spectroscopy (D.L.O.S.). The σ°n cross section exhibits both a resonant and non resonant character. The former corresponds to the internal transition 5T2-5E of Cr2+ while the threshold of the second allows us to locate the Cr2+/Cr3+ level below the conduction band. The absolute photoionization cross sections towards the two bands are very similar. In particular no selection rule seems to work.

High resolution transmission electron microscopy (HRTEM) has been performed on cross-sectional specimens from high dose (1016 cm−2) H+ implanted (100) GaAs (300 keV at room temperature). It was found that annealing at 500°C created small (20-50Å) loops on {111} near the projected range (Rp)(3.2 μm). At 550-600°C, voids surrounded by stacking faults, microtwins and perfect dislocations were observed near the Rp. A phenomenological model explaining the observed results is proposed.

Some recent data on minority carrier diffusion length MCDL in GaAs and certain optoelectric parameters of LEDs obtained by the authors as well as reported in the literature have been analysed to shed light on the probable configuration of certain deep levels in GaAs and related compounds. The practical implications of the results obtained are discussed from the view point of the mechanism of slow degradation of the related optoelectronic devices.

The simultaneous molecular beam epitaxy (MBE) growth of (100) and (110) GaAs/GaAsintentionally doped with Si(∼lE16/cm^3) was studied as a function of substrate temperature, arsenic overpressure, and epitaxial growth rate. The films wereanalyzed by scanning electron and optical microscopy, liquid helium photoluminescence (PL), and electronic characterization.

For the (110) epitaxal layers, an increase in morphological defect density and degradation of PL signal was observed with a lowering of the substrate temperature from 570C. Capacitance-voltage (CV) and Hall Effect measurements yield room temperature donor concentrations for the (100) films of n∼l5/cm^3 while the (110) layers exhibit electron concentrations of n∼2El7/cm^3. Hall measurements at 77K on the (100) films show the expected mobility enhancement of Si donors, whereas the (110) epi layers become insulating or greatly compensated. This behavior suggests that room temperature conduction in the (110) films is due to a deeper donor partially compensated by an acceptor level whose concentration is of the same order of magnitude as that of any electrically active Si. Temperature dependent Hall effect indicates that the activation energy of the deeper donor level lies ∼290 meV from the conduction band. PL and Hall effect indicate that the better quality (110) material is grown by increasingthe arsenic flux during MBE growth. The nature of the defects involved with the growth process will be discussed.

A new eutectic etchant for GaAs has been developed to display (a) the normal etch pit patterns, but also to reveal (b) rectangular, (c) shallow matrix and (d) raised geometric patterns. Results on various GaAs substrates, ranged from undoped to In-, Cr-, Te-, Si-doped materials, show a general trend: The materials having the numbers of (a), (b) and (c) etched patterns are roughly in the above order (from high density to low density). Whereas, for the density of the raised geometric patterns, the ranking is reversed. It is concluded that the major factor in developing the (a), (b) and (c) etched patterns is due to the stress, while the (d) pattern may be due to dopant and its influence on Ga to As bondings.

The kinetics of charge capture by deep donors in AlxGa1-xAs have been measured. The time dependence indicates that a single energy cannot be used to describe the trap. A model assuming thermally activated capture into a resonance in the conduction band with a range of energies gives excellent fits to the data and provides a measure of the energy range for the trap. This model is consistent with the large lattice relaxation model for DX centers. The increase of the activation energy for capture as the Al mole fraction is decreased contradicts the model which attributes the decay of the persistent photoconductivity to tunneling through the heterojunction barrier in modulationdoped structures.

ZnO varistors are polycrystalline materials which have highly non—linear current/voltage characteristics controlled by depletion regions around the grain boundaries. Dissolved transition metals at concentrations of about 1 at.% are required to achieve this large nonlinearity, but their role is unclear. To address this issue we have usedthe technique of photothermal deflection spectroscopy to measure the optical absorption of varistors containing Co or Mn, both common dopants. Prominent peaks and edges appear in the spectra, and are associated with substitutional Co2+and Mn2+ ions whose ground states are deep within the ZnO bandgap. Electro— and photoluminescence spectra show Stokes shifted peaks for some of these transitions. The spectral dependence of the photoconductivity shows that some of the absorption features correspond to ionization of the impurities. This result is used to show how the dark impact ionization of these impurities due to a high applied voltage can contribute to the current/voltage nonlinearity.

Our study shows that the isolation—degradation in semi—insulating GaAs substrate is closely related to dry—processes during the device fabrication. It was found that EL2, the major electron trap in undoped LEC semiinsulating GaAs, could be passivated by plasma—assisted etchings or depositions. The passivation of EL2 causessurface leakage and leads to crosstalk in GaAs ICs.

Laser induced defects in (AI,Ga)As heterostructures have been investigated. Luminescencetopography reveals three different defects, a luminescent B, a nonradiative D as well asdark line defects (DLD). Luminescence and excitation spectra together with TEM measurements indicate a point defect or point defect complex for B and D. Defect B is described by a configuration coordinate (CC-) model with low vibrational energies. Defect DLD consists of extended dislocations.

A deep photoluminescence (PL) band peaking at 1.08 eV in Cu-doped GaP has been studied by means of optically detected magnetic resonance (ODMR). We report an intense S=l ODMR spectrum arising from this PL band. The signal is strongly anisotropic and consistent with a center of triclinic symmetry. Some of the ODMR transitions show a well resolved hyperfine structure in agreement with the nuclear spin I=3/2 of Cu, thus suggesting the presence of Cu in the defect.

A review of the Transmission Electron Microscopy and Scanning Transmission Electron Microscopy techniques used for electronic defect identification is presented. The structural, chemical and STEM based spectroscopy methods for electronic defect analysis are discussed along with selected examples.

We propose a new approach to the defect characterization in semiinsulating (SI) GaAs which combines the high spatial resolution and scanning capability of the Electron Beam-Induced Current (EBIC) mode of Scanning Electron Microscopy (SEM) with the advantages of optical and thermal spectroscopies employed in the identification of deep levels. In the PHOTO-EBIC approach a DC electron beam and a chopped subbandgap monochromatic light impinge on the SI GaAs through a semi-transparent Au electrode. The photoinduced modulation of the EBIC as a function of the subbandgap energy of incident photons constitutes a structure which corresponds to the photoionization of deep levels. In the thermally stimulated EBIC (TS-EBIC) the deep levels are filled at low temperature by the excess carriers generated by an electron beam. Subsequently, the changes of EBIC as a function of temperature constitute a spectrum of peaks which correspond to different deep levels. The peak position determines the deep level energy while the magnitude of peaks can be used for the assessment of the relative concentration of deep levels located within the small volume probed by the electron beam.

The time resolved heat pulse generated by above band gap light is studied at 2 K in undoped, semi—insulating GaAs. The phonon lineshape changes with irradiation by 1.1 micron below gap light. The changes in phonon lineshape are reversed by raising the sanple teaperature to 130 K and recooling to 2M. The results provide strong evidence for the change in acoustic phonon scattering when the defect EL2 is transferred to its metastable state. The phonon scattering anisotropies observed for the [100] and [111] directions is indicative of an anisotropic phonon—defect interaction.

Recently developed tunable color center lasers allow to extend the experimental technique of excitation spectroscopy to the 1–2 μm region. This spectral range is of special interest for the study of luminescent defects in silicon. We discuss the color center laser systems available at present and their application to defect spectroscopy. As an example, results on the 0.767 eV (P line) defect in silicon are presented. Excitation spectroscopy reveals several high lying excited electronic states. They are interpreted as effective—mass—like states of a pseudo-donor with an ionization energy of 34.3 meV.

Infrared band—mode and LVM absorption is illustrated for a range of impurities and impurity—complexes in silicon and gallium arsenide. We discuss the effects of changes in the local force constants and contributions to the dipole moment resulting from displacements of host lattice atoms. The difficulties in establishing absolute calibrations relating the strength of the absorption to the concentration of defects are highlighted. Our purpose is to show how the measurements lead to characterization of crystals and how they complement other diagnostic techniques to evaluate effects of irradiation, heat treatments, diffusions etc.

We report the first study of the effect of hydrostatic pressure on the annealing of defects in Si and GaAs. It is shown that the application of hydrostatic pressure enhances the annealing rate in these materials. Analysis of the data yields the lattice volume relaxation accompanying annealing.

Positron measurements on boron doped CZ—silicon show that clusters of oxygen interstitials trap positrons. Depending on whether a vacancy is associated to this cluster or not, the positron lifetimes exhibit changes from 240 to 100 ps. The positron data indicate the nature of the initial —or precursor — stages for thermal donor formation.

The perturbed angular correlation method (PAC) is applied to semiconductors. This technique is based on the detection of the electric quadrupole hyperfine interaction by means of radioactive nuclei. The highly localized sensitivity of the PAC-method favours the investigation of localized distortions of the lattice due to impurities as donor or acceptor atoms.

Results are given for radioactive 111Cd atoms in the semiconductors In2 Te5, ZnO, and Si. The observed electric field gradients (EFG) and their orientations with respect to the crystal axes yield information on the local structure around the probe atoms. In Na—or Li—doped ZnO the formed Na—O—In (or Li—O—In) complexes show identical axial symmetric EFG tensors. In the case of In2Te5 acceptor level energies could be deduced from the temperature dependence of the EFG.