Dominant Impurity Research Articles

Properties of Epitaxial GaAs Layers from a Triethyl Gallium and Arsine System

epitaxial layers with low electron concentrations were obtained from an alkylgallium and arsine system by use of triethylgallium. The highest Hall mobility of the layer, with an electron concentration of at 77°K was 120,000 cm2/V sec. Carrier concentration and carrier type of the layer could be changed in the range of from 1012 to ∼ 1016/cm3 by changing the arsine to triethyl gallium mole ratio introduced into a deposition zone. This fact was expected to be due to the amphoteric impurity sharing between the arsenic and the gallium sites of crystal.Although the extension of carrier concentration to the lower range resulted from impurity compensation, mobility data of the layers of electron concentrations higher than about 1014/cm3 were almost the same as those from the usual system. Dominant acceptor impurities observed in the photoluminescence measurements were discussed and were correlated with amphoteric silicon and carbon impurities. This was consistent with the result obtained on the impurities of the layer by mass spectroscopic analysis.

Deep impurity levels in epitaxial PbS films

Compensation of sulfur vacancies in hot wall grown epitaxial films produces materials with very low carrier concentrations, p 77 k ∼3 × 10 22/m 3). At these lower concentrations, an impurity center is found, tentatively identified with the dominant Si impurity, and which produces a deep electron trap and acceptor level 0.079 eV above the valence band. At low temperatures, the lifetime rises to 65 milliseconds indicating minority carrier trapping.

Heat treatment of ion implanted GaAs

Abstract Rutherford backscattering, electron spectroscopy (ESCA) and transmission electron diffraction have been used to analyse SiO2 or Si3N4 encapsulated GaAs specimens, heat treated at 600°C or 750°C. The nitride layer is found to be the better of the two encapsulants as it inhibits oxygen in diffusion and the formation of β-Ga2O3. Lattice damage caused during ion implantation is found to enhance the formation of Ga2O3 in specimens encapsulated with SiOz, and it is concluded that after heat treatment of these specimens, oxygen may be the dominant impurity.

A combined LEED, AES and XPS study of the ZnO {0001} polar surfaces: I. LEED, AES and XPS of contaminated surfaces

The {0001} polar surfaces of ZnO single crystals have first been examined after a chemical treatment involving HCl and H 3PO 4 and a 24 hr bakeout at 250 °C. The impurities detected on the (000 1 )-O surface with AES were carbon, chlorine, phosphorus and to a lesser extent sulphur. On the (0001)-Zn surface, carbon, chlorine and sulphur were the dominant impurities, while the phosphorus signal was less important. These results were confirmed by XPS measurements on frehsly etched surfaces. The AES spectra were recorded as distribution curves N( E). Averaging, curve-fitting and related numerical techniques were used to obtain high resolution spectra, enabling the identification of the phosphorus L 1-transitions. The etched surfaces were cleaned progressively using argon ion bombardment and ohmic heating. It has been consistently observed that the clean surfaces exhibit primitive (1 × 1) structures. Superstructures such as ( 3 × 3 ) on the (000 1 )-O surface, and (4 3 × 4 3 ) and (3 × 3) on the (0001)-Zn surface, were repeatedly observed at discrete spots of contaminated surfaces. A clear correlation with impurities as observed by AES however could not be found. Facetting was observed after prolonged heating.

Minority carrier diffusion length in liquid epitaxial GaP

Using a Schottky diode photocurrent technique, investigations have been made of the room temperature value of minority carrier diffusion length in liquid epitaxial GaP grown on both (111) and (100) oriented pulled GaP substrates. Results are presented for undoped layers and layers doped separately with S, S and N, Te, Zn, and Zn and O, to cover a range of impurity concentration in the GaP. The measured values of minority carrier diffusion length are found to depend on the concentration of the dominant impurity and, for the undoped and Zn doped layers, also on the growth orientation of the substrate. From the dependence of the minority carrier diffusion length on majority carrier concentration we infer the dominant room temperature recombination process in the layers. In our undoped layers this process is believed to correspond to recombination via residual Si substituted on P sites. In Te, S, Zn, and Zn, O doped layers the dominant recombination mechanism can be attributed to a non-radiative band-band Auger process, although in the case of the Zn, O doped layers a competing recombination process is observed which is believed to correspond to recombination via centres formed by unpaired O and Zn defects. The lifetime for this competing process is predicted to be sensitive to annealing.

Effect of Gold Coating on Sorption Characteristics of CO, Sulphur, and Other Gases on Stainless-Steel Sheet

Auger electron spectroscopic observations of the vacuum-deposited gold surface in comparison with bare stainless-steel surface have been made under varying vacuum conditions. The C and O peaks for the gold surface were negligibly small whereas those for the bare surface were rather intense and increased with time of exposure to primary electron bombardment. Decrease of the sulphur peak with increase of C and O peaks was observed for the bare surface which suggests that the impurity sulphur located on the stainless steel surface is covered by an adsorbed CO layer. Sulphur is the dominant impurity on a stainless steel surface after 700 °C flashing, but a very weak sulphur peak is observed for the surface covered by approximately 10 layers of vacuum-deposited gold film. Migration of sulphur from a bare stainless-steel surface to the gold-covered part of the surface has also been observed as a function of temperature.

Effects of nonequilibrium chemistry on electrical properties of solid propellant rocket exhaust plumes

Application of basic chemical kinetic and gasdynamic considerations to the problem of calculating electrical properties of turbulent afterburning exhaust plumes of solid propellant rocket motors is discussed. The sources of free electrons are described, and the importance of incorporating chemical kinetic (rather than thermochemical equilibrium) data is illustrated by reference to several sample calculations. It is shown that for systems in which potassium is the dominant impurity, above-equilibrium electron concentrations are formed, principally viaK+C1→K++C1- followed by C1-+H→HC1+e- The free radical concentrations are produced in above-equilibrium concentrations from the H2-CO-Cl-O2 afterburning reactions. Exhaust plume properties are shown to be sensitive to values selected for rate coefficients of several reactions, and the need for more accurate determinations of these rate coefficients is thus demonstrated. The accuracy of the calculations is further limited by uncertainties in the gasdynamics of the turbulent mixing process. Within the limits of error imposed by these uncertainties, however, the model described does account adequately for experimental observations.

Electrical conduction and G—R noise in n-type α-Fe 2O 3

Electrical conductivity, Seebeck coefficient and generation-recombination (g–r) noise of several natural single crystals of α-ferric oxide, containing Sn or Ti as dominant impurities were measured, in the temperature range 55 K–300 K. It was concluded that the conduction is almost completely determined by charge carriers in the narrow 3d band of iron. Two samples, however, showed at low temperatures impurity conduction. The noise spectra can be interpreted by assuming that electron transitions occur between the 3d level of iron and the nearly empty sp band of oxygen. It was found that the energy difference between the 3d level and the sp band is about 0.20 eV and that the drift mobility for electrons in the sp band is about 10 3 cm 2/Vs at temperatures between 110 K and 150 K.

Investigation of the Electron Statistics of the Neutral Acceptor Level of Gold in Germanium

Detailed correlation of Hall Effect and resistivity data with electron statistics relations have been performed for experimentally determining the degeneracy ratio for the lower acceptor level of gold in germanium. Information on the density of gold in the germanium crystals is deduced through growing indentical crystals except that the dominant shallow impurity is a donor in one case and an acceptor in the other. A value for the degeneracy ratio of four is obtained. The Hall effect data is supported by neutron activation analysis data.

Electron paramagnetic resonance of Fe 3+ in natural topaz

The EPR spectra of Fe 3+, the dominant paramagnetic impurity in natural topaz, showed marked “super- hyperfine” structure allowing the crystal site to be determined. Angular dependent spectra revealed strong zero-field splitting as predicted by an appropriate spin-Hamiltonian.

EFFICIENT ELECTROLUMINESCENCE FROM GaAs DIODES AT 300°K

The light-emitting diodes described in this Letter differ from standard type diodes insofar as the amphoteric dopant Si is the dominant impurity on both sides of the junction. The p-n junction is completely solution regrown. The highly compensated p region gives rise to a wide active region up to 50 μ in width. The interesting feature of these diodes is their high external quantum efficiencies at 300°K. Values up to 6% have been measured on diodes, when an antireflecting coat has been applied.

Internal friction due to chromium and iron in magnesium oxide

Internal friction in magnesium oxide in the kc range shows a broad relaxation peak with a maximum near 850°C. The peak height is proportional to the chromium content, or to the iron content, whichever is the dominant impurity. The activation energy of the peak is 2.1 ± 0.1 eV, giving a pre-exponential frequency factor of 3 × 10 14 sec −1, near that for a simple atomic diffusion process. A modified bound-vacancy model is discussed. The experimental results are consistent with such a model, but the agreement is not sufficiently clear-cut to allow positive identification of the relaxation parameters with those of vacancy diffusion.

Microsegregation and the Tendency for Pitting Corrosion in High‐Purity Aluminum

Single crystals of 99.99%, 99.999%, and 99.9999% Al have been grown from the melt under conditions controlled to produce either homogeneous solute distributions, or microsegregation (on the scale ∼100μ) of the dominant residual impurities Fe, Cu, and Si. Exposure of samples to resulted in a fine‐scale pitting of segregated specimens while homogeneous specimens remained free of such pits. Various mechanical and annealing treatments did not disturb this contrast and, in general, the pitting could be quantitatively related to a previous segregation study in these metals. Polarization measurements showed that the main effect of segregation is to produce a decrease in the cathodic overvoltage which shifts the corrosion potential into a range where pitting occurs. Since the two less pure grades exhibited segregation in the same size scale, and were relatively indistinguishable, it seems that the distribution, rather than the total amount of residual impurity, is more important in producing a tendency for pitting.

Preparation of High‐Purity Indium Arsenide

The purest indium arsenide so far reported has a carrier concentration of about 1.3.1016 electrons/cm3 at room temperature. This is several times the intrinsic value and it has been suggested that the limiting impurity may be sulfur originating in the arsenic component. Arsenic has been prepared by the thermal decomposition of highly purified arsine gas and has been combined with samples of indium purified by a variety of processes. Mass spectrographic analysis of the resultant ingots showed in all cases a sulfur content less than 0.05 ppm. The purest sample had a Hall coefficient of 795 cm3/coulomb at 77°K, corresponding to an electron concentration of 8.1015/cm3 while the Hall mobility was 75,700 cm2/v/sec. Analytical techniques failed to detect the prime source of the free electron concentration, but it is concluded that sulfur is not the dominant impurity in these samples.

The preparation of single-crystal ingots of silicon by the pulling technique

The construction and operation of a laboratory furnace for preparing monocrystals of silicon by the pulling technique are described. The design allows for close observation of the growth front of the ingot during its preparation. It has been found possible to assess the quality of high-grade silicon, and also to obtain an indication of the concentration of dominant impurities responsible for the measured resistivity by comparison with computed distribution curves.