Detaching the crystals from the melt revealed the real state and dynamic change of intrinsic point defects. From this observation it is confirmed that the predominant point defects near the melting point are vacancies. Clusters of interstitial-type dislocation loops (CDL) are eliminated by taking an extremely low growth rate under 0.2 mm/min and nitrogen doping. The anomalous oxygen precipitate (AOP) of the crystals grown in a nitrogen ambient is enhanced. AOP and ring-oxidation induced stacking fault (R-OSF) coexist at the periphery in nitrogen doped crystals. Almost all crystals have defect boundaries between periphery and center region which may be attributed to a stress field in the crystals during growth.

The structural characterization of the oxygen related lattice defects formed under different thermal cycling conditions is discussed. The present understanding on the nature of rod-like defects and oxide precipitates is reviewed. Attention is given to the whole lattice defect spectrum which is induced by the oxygen precipitation. The influence of carbon and dopants on the defects is discussed.

A method will be presented, which allows the quantitative determination of distributions of single vacancies in bulk silicon. The method uses deep level transient spectroscopy (DLTS) measurements of the platinum or gold concentration after diffusion at a low temperature. An analytical expression allows the calculation of the vacancy concentration from the measured platinum or gold concentration. Vacancy concentrations vary at least from 2.0×1012 to 2.2×1014 cm3 in float zone silicon. The vacancy concentrations in Czrochalski (CZ) silicon are in the range of 4×1012 to 2×1013 cm3. Microwave photoconductive decay instead of DLTS allows much faster measurements of vacancy distributions on whole wafers. Furthermore, both methods allow the investigation of oxygen precipitation in CZ silicon.

The nature and radial distribution of crystallographic micro-defects in CZ-grown silicon crystal wafers which exhibit OSF ring were investigated. With the difference in copper decoration XRT image and in temperature dependence of oxgen precipitation, four coaxial ring regions were clearly identified. In the OSF ring region, oxgen precipitation takes place even at relatively high temperatures around 1, 100°C. Gold diffusion experiments were also carried out, for which the ‘kick-out mechanism’ was considered to reveal the density distribution of sinks for interstitial silicon. A semi-quantitative schematic model describing the density distribution of the precipitation nuclei as a function of critical size of the nuclei for each of the four ring regions is derived. The nuclei that are stable at high temperature act as sinks for interstitial silicon atoms, generating stacking faults.

We have studied defects in Cz-grown single crystal silicon by utilizing a variable energy positron beam and positron lifetime spectroscopy in conjunction with surface photovoltage measurements. We present results for the depth profile of defects obtained from the Doppler broadening spectra measured by implanting variable energy positrons at different depths ranging from the surface down to ∼ 1 /xm deep. We have also measured positron lifetime spectra at different locations on a wafer and have obtained a radial variation in the density of the vacancy-type defects.

Microdefects, revealed as ‘flow patterns’ by preferential etching using Secco's etchant, in as-grown silicon crystals have been investigated by means of a transmission electron microscopy and a preferential etching. In as-grown CZ crystals, grown at the pulling speeds of 0.4 or 1.4 mm/min, dislocation loops and clusters were observed with TEM. The dislocation loops in both crystals are interstitial type. From a thermal behavior of flow patterns by heat treatments, we confirmed that the defects revealed as flow patterns in CZ crystals do not have a similar nature of that in D-defect region of FZ crystals.

We investigated the effect of D-defect in CZ silicon single crystals on the oxygen precipitation by two-step thermal treatments consisting of the first annealing in nitrogen ambient at 1073K and the second annealing in dry oxygen ambient at 1273K. The density of D-defect was measured by counting ‘flow patterns’ using an optical microscope after preferential etching in Secco's solution for 30 minutes. It was found that the amount of oxygen precipitation along the growth axis was not affected by D-defect. The predominant factor of the oxygen precipitation after the two-step thermal process is the nuclei of oxygen precipitation generated around 723K during CZ crystal growth.

We investigated phenomena of oxygen precipitation nonuni-formity along crystal growth axis due to different thermal histories during CZ crystal growth. The oxygen precipitation process employed in this paper was two-step thermal treatments consisting of the first annealing in nitrogen ambient at 1073K for 4 hrs and the second annealing in dry oxygen ambient at 1273K for 16 hrs. The amount of the oxygen precipitation at the shoulder of a silicon single crystal was higher than the one at the tail end. We found this nonuniform distribution profile was due to the thermal history around 723K during crystal growth. Such an nonuniformity could be improved remarkably by adding a preannealing in dry oxygen ambient at 723K for 2 hrs before the two-step thermal treatment.

We have studied the nucleation of oxygen precipitates in Czochralski (Cz) Si crystal quenched from high temperature (1390°C). We observed that the oxygen precipitation was enhanced by the quenching treatment. We found the density of precipitates in the quenched crystal depended on quenching temperature and that nuclei for oxygen precipitates were introduced during quenching. We studied these nuclei using infrared absorption (IR) and positron annihilation techniques. In order to clarify the state of the nuclei, the quenched specimens were irradiated with 3-MeV electrons at a dose of 1×1018e/cm2 and vacancy-oxygen complexes were introduced. Positron lifetime spectra and IR absorption spectra for these specimens were measured as a function of isochronal annealing temperature. From the annealing behavior of the vacancy-oxygen complexes, it was found that oxygen clusters are introduced by the quenching and these clusters are the nuclei for the enhanced precipitation of the quenched Si crystal.

Depth profiles of thermal donors introduced by heat treatment at 450°C in Czochralski-grown n-type silicon have been studied through capacitance-voltage measurements of Au Schottky diodes in the oxygen concentration range 8.1×1017 to 15.3×1017 cm3 Thermal donor concentrations increase with depth and their depth profiles are fitted to the error function equation. The obtained diffusivity decreases with annealing time and is higher for samples with the lower initial oxygen concentrations. Combining with the infrared absorption measurements, it is found that the curves of the diffusivity as a function of loss of interstitial oxygen coincide with each other. The similar tendency is observed on the oxygen diffusivity evaluated with secondary ion mass spectrometry. These results indicate that the oxygen diffusivity at 450°C is related to both the outdiffusion and clustering of oxygen. Depth profiles of thermal donors formed at 650°C are also reported.

Self-interstitial sink efficiencies of dislocations γ were measured in gold doped FZ (111) and (100) samples, we found respectively γ=0.4–0.5 and γ=0.2–0.3. γ is probably sensitive to dislocation character and to the deformation process.

lmpurity effects on the mobility of dislocations and dislocation generation from generation centers in III - V compound semiconductor crystals are first reviewed on the basis of experimental observations of dynamic behavior of individual dislocations. Dislocation multiplication process is then discussed to account for experimental stress-strain characteristics of these materials obtained in mechanical tests. Using all of such knowledge on dislocation processes in the compound semiconductor crystals, an argument is developed to show how impurities play the role in reducing grown-in dislocations in crystals of these materials. It is shown that immobilization of dislocations caused by impurity gettering plays the decisive role and results in even the growth of dislocation-free crystals.

The novel infrared imaging technique for assessment of undoped semi-insulating (SI) GaAs substrates known as Reverse Contrast is known to result from absorption from point defects whose concentrations approximately anti-correlate with those of EL2, deep donor defects. The absorption that occurs within - 65 meV of Eg in cooled samples is sufficiently strong that commercial wafers can be mapped with simple infrared CCTV imaging equipment. RC defects are thought to be very deep acceptors with an ionization energy close to the Conduction Band. Concentrations of RC defects are not measurable in SI GaAs as they are un-ionized in the dark. Like EL2 defects they can be photo-quenched by irradiation with mid-gap light.

In this paper, we present novel Hall Effect measurements on very lightly Te-doped n-type GaAs where at least a fraction of RC defects are ionized. A permanent increase in the carrier concentration is observed after photo-quenching corresponding to the bleaching of RC defects. The carrier concentration returns to its initial value at the same temperature at which the absorption of RC defects is recovered. This result allows a calibration for the absorption coefficient to be found.

Properties of medium-deep traps in n-type undoped GaAs crystals grown by arsenic-pressure controlled Czochralski (PCZ) method were studied by using capacitance transient spectroscopy (CTS) and temperature-dependent Hall (TDH) measurement. EL3 and EL6-like (EM2) traps were dominant medium-deep traps in D LTS measurements. The dependence of EM2 peak height on the duration of filling pulse and the detailed analysis of CTS showed that the trap EM2 spectrum consisted of three electron traps which had thermal emission activation energies of approximately 0.35 eV and various capture cross sections with activation energies for electron capture. On the other hand, the trap EL6 spectrum in n-type LEC GaAs was described by two levels of traps with activation energies of 0.32 eV and 0.33 eV for electron emission, respectively. It was concluded that so-called EL6 formed a family and some of its components were classified as defects with large lattice relaxation.

Bulk ZnSe single crystals were grown by annealing a CVD grown polycrystalline ingot in a selenium atmosphere for two weeks at 1000°C. To identify the defect structures closely related to the observed grain growth, point defects in bulk ZnSe were subsequently investigated using the positron annihilation technique. A striking result has been obtained; the selenium interstitial type defects were dominantly observed in the crystals grown under a selenium ambient. The fraction of annihilations from the trap states at selenium interstitial type defects in ZnSe increased with increasing the selenium pressure in the annealing ampoule. These results indicated that selenium interstitial type defects enhanced the atomic migration in the crystal and strongly assisted the recrystallization by dislocation climb.

The microstructure and microchemistry of a number of melt textured CuInSe2 ingots prepared from a variety of starting charge compositions have been investigated using a combination of TEM, EPMA and Auger spectroscopy. If a stoichiometric starting mixture is used, In-rich and Cu-rich precipitates are found at the first and last to freeze zones of the ingot respectively, accompanied by an intervening mid-portion of inclusion free (although slightly off-stoichiometry) CuInSe2 We have found that in order to achieve an optimum matrix composition, a Cu-rich charge is required; however, this leads to a fine distribution of copper selenide particles throughout the ingot. If the starting charge is In-rich, then the boule contains In-rich precipitates and the matrix composition is In-rich and Cu-deficient. These observations are correlated with the observed electrical characteristics of the boules.

The variation of the composition within the narrow range of off stoic hiometry allowed for compounds is determinant for the population of various intrinsic point defects. As such concentration fluctuations result in inhomogeneities of defect distributions. On the basis of statistical thermodynamics, applied to concentration fluctuation analysis in the III-V compounds, a thermodynamic stability length is defined and calculated as a function of temperature for GaAs, GaSb and GaP. This thermodynamic stability length defines the scale above which full composition homogeneity is unattainable.

Heavily carbon-doped GaAs thin films with a hole concentration of 5.8 × 1020 cm-3, grown by metalorganic molecular beam epitaxy (MOMBE), were annealed at 900°C for 30 minutes. The microstructural changes due to annealing were investigated by transmission electron microscopy. Electron diffraction study showed some evidence of carbon clustering on {111} in as-grown samples. A high density of precipitates was found in the annealed sample, together with a decrease of the lattice contraction and hole concentration. In the as-grown layer, misfit dislocations with only one type of Burgers vector were observed, while misfit dislocations with the several Burgers vectors were observed in [110] direction after annealing. The density of misfit dislocations in both <110> directions increased significantly even though the lattice contraction in carbon-doped GaAs decreased after annealing. A model is proposed to explain the change of misfit dislocation density in heavily carbon-doped GaAs layer.

Thermal stability of SiHn (n=1∼4) configurations in FZ silicon crystals grown in Ar/H2 has been investigated by means of infrared absorption spectroscopy. Infrared absorption peaks at 2210, 2192, 2123 and 1946 cm−1, which are due to SiH4, SiH3, SiH2 and SiH units in silicon lattice, has been observed. It is found that the concentration of SiH4 and SiH increase with the decrease in SiH2 and SiH3 concentration at 500°C, and vice versa at 600°C. Annealing results suggest thermally induced structural transformations of SiHn configurations. We propose a model of the transformations through the cleavage of adjacent Si-H bonds to form a Si-Si bond and a H2 molecule, as well as the reaction of a H2 molecule with a Si-Si bond.

We investigate the intrinsic point defects in epilayers grown by atomic layer epitaxy (ALE). Ga vacancies and antisite As atoms in the epilayers are detected by photoluminescence spectroscopy. This shows that the ALE epilayer was grown under As-rich conditions. We propose increasing the TMG flux to reduce the number of point defects. With this method, the number of point defects in ALE epilayers can be decreased to less than that in conventionally grown epilayers. Moreover, it is'found that these point defects are formed by the incomplete Ga coverage, not by the steric hindrance as previously suggested. The carbon concentration is decreased by one order of magnitude by using nitrogen instead of hydrogen as the carrier gas. As an application of this low defect density, we fabricated a GaAs/AlAs resonant tunneling diode and observed the negative resistance at room temperature.