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Hydrogen-related effects in crystalline semiconductors

Description: Recent experimental and theoretical information regarding the states of hydrogen in crystalline semiconductors is reviewed. The abundance of results illustrates that hydrogen does not preferentially occupy a few specific lattice sites but that it binds to native defects and impurities, forming a large variety of neutral and electrically active complexes. The study of hydrogen passivated shallow acceptors and donors and of partially passivated multivalent acceptors has yielded information on the electronic and real space structure and on the chemical composition of these complexes. Infrared spectroscopy, ion channeling, hydrogen isotope substitution and electric field drift experiments have shown that both static trigonal complexes as well as centers with tunneling hydrogen exist. Total energy calculations indicate that the charge state of the hydrogen ion which leads to passivation dominates, i.e., H/sup +/ in p-type and H/sup /minus// in n-type crystals. Recent theoretical calculations indicate that is unlikely for a large fraction of the atomic hydrogen to exist in its neutral state, a result which is consistent with the total absence of any Electron Paramagnetic Resonance (EPR) signal. An alternative explanation for this result is the formation of H/sub 2/. Despite the numerous experimental and theoretical results on hydrogen-related effects in Ge and Si there remains a wealth of interesting physics to be explored, especially in compound and alloy semiconductors. 6 refs., 6 figs.
Date: August 1, 1988
Creator: Haller, E. E.
Partner: UNT Libraries Government Documents Department

Detector materials: germanium and silicon

Description: This article is a summary of a short course lecture given in conjunction with the 1981 Nuclear Science Symposium. The basic physical properties of elemental semiconductors are reviewed. The interaction of energetic radiation with matter is discussed in order to develop a feeling for the appropriate semiconductor detector dimensions. The extremely low net dopant concentrations which are required are derived directly from the detector dimensions. A survey of the more recent techniques which have been developed for the analysis of detector grade semiconductor single crystals is presented.
Date: November 1, 1981
Creator: Haller, E.E.
Partner: UNT Libraries Government Documents Department

Hydrogen in germanium

Description: Hydrogen is shown to form molecular acceptors and donors in pure germanium. Piezospectroscopy reveals that the hydrogen-related shallow donor D has non-tetrahedral symmetry. One hydrogen atom is incorporated in D as shown with an isotope shift in the donor ground state. Oxygen is also involved in the formation of D. The hole emission rates of two copper--hydrogen acceptor complexes were determined with Deep Level Transient Spectroscopy. They are e/sub 1//sup Cu-H/ = 1.5 x 10/sup 8/ T/sup 2/ exp (-.195 eV/kT) K/sup -2/ s/sup -1/ and e/sub 3//sup Cu-H/ = 5.0 x 10/sup 8/ T/sup 2/ exp (-.068/kT) K/sup -2/ s/sup -1/.
Date: September 1, 1978
Creator: Haller, E.E.
Partner: UNT Libraries Government Documents Department

New method to determine the chemical composition and structure of non-elemental acceptor and donor centers in ultra-pure germanium

Description: A new approach towards the understanding of hitherto unknown, non-elemental acceptors and donors which can limit the purity of ultra-pure germanium has been explored for a specific pair of shallow centers, designated A/sub 2/ and D. Using photoelectric spectroscopy, we have demonstrated that an isotope shift in the ground-state binding energy occurs when the germanium crystals are grown in pure deuterium instead of in the usual pure hydrogen atmosphere. This isotope shift is the most direct proof of the presence of hydrogen atoms in the centers A/sub 2/ and D. Applying uniaxial stress to Ge samples containing A/sub 2/ and D, we show that the symmetry and structure of the centers can be explored. The knowledge of the chemical composition and the structure of the non-elemental centers will allow development of methods to reduce and keep their concentrations to acceptable levels.
Date: October 1, 1977
Creator: Haller, E.E.
Partner: UNT Libraries Government Documents Department

Defects in germanium: new results and novel methods

Description: Recent results obtained from quenching experiments, electron, gamma-ray, neutron and proton irradiation of germanium are reviewed. Major emphasis is given to the introduction of novel techniques for the study of shallow and deep levels. Explicitly introduced are Photothermal Ionization Spectroscopy (also called Photoelectric Spectroscopy), Deep level Transient Spectroscopy and High-Q Electron Paramagnetic Resonance. Using as examples the recently discovered hydrogen-related centers and the lithium/lithium-oxygen system in germanium it is shown that a combination of techniques can yield information on composition and structure of defects.
Date: September 1, 1979
Creator: Haller, E.E.
Partner: UNT Libraries Government Documents Department

Fabrication techniques for reverse electrode coaxial germanium nuclear radiation detectors

Description: Germanium detectors with reverse polarity coaxial electrodes have been shown to exhibit improved resistance to radiation damage as compared with conventional electrode devices. However, the production of reverse electrode devices involves the development of new handling and fabrication techniques which has limited their wider application. We have developed novel techniques which lead to a device which is simple to fabricate, environmentally passivated and surface state adjusted.
Date: November 1, 1980
Creator: Hansen, W.L. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

Electronic properties of hydrogen-related complexes in pure semiconductors

Description: Hydrogen has been shown to activate the neutral impurities carbon, silicon and oxygen in ultra-pure germanium and form shallow level complexes. The double acceptors beryllium and zinc in silicon and germanium, as well as the triple acceptor copper in germanium, can be partially passivated, leading to single hole acceptors. The study of the electronic level spectrum of the single carrier bound to these centers at low temperatures has provided much information on symmetry and composition. Most centers reveal a symmetry axis along (111) and are static. In some cases hydrogen has been found to tunnel between equivalent real space positions. Photothermal Ionization Spectroscopy (PTIS) has been the most important tool for the study of the optical transitions of the hole (electron) in these hydrogen containing complexes. This photoconductivity technique combines high sensitivity with high resolution and permits the study of shallow acceptors or donors present at concentrations as low as 10{sup 8} cm{sup {minus}3}. Even lower limits may be attained under favorable circumstances. 51 refs., 6 figs.
Date: July 1, 1990
Creator: Haller, E.E.
Partner: UNT Libraries Government Documents Department

High-purity germanium crystal growing

Description: The germanium crystals used for the fabrication of nuclear radiation detectors are required to have a purity and crystalline perfection which is unsurpassed by any other solid material. These crystals should not have a net electrically active impurity concentration greater than 10/sup 10/cm/sup -3/ and be essentially free of charge trapping defects. Such perfect crystals of germanium can be grown only because of the highly favorable chemical and physical properties of this element. However, ten years of laboratory scale and commercial experience has still not made the production of such crystals routine. The origin and control of many impurities and electrically active defect complexes is now fairly well understood but regular production is often interrupted for long periods due to the difficulty of achieving the required high purity or to charge trapping in detectors made from crystals seemingly grown under the required conditions. The compromises involved in the selection of zone refining and crystal grower parts and ambients is discussed and the difficulty in controlling the purity of key elements in the process is emphasized. The consequences of growing in a hydrogen ambient are discussed in detail and it is shown how complexes of neutral defects produce electrically active centers.
Date: October 1, 1982
Creator: Hansen, W.L. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

Assessment of present and future large-scale semiconductor detector systems

Description: The performance of large-scale semiconductor detector systems is assessed with respect to their theoretical potential and to the practical limitations imposed by processing techniques, readout electronics and radiation damage. In addition to devices which detect reaction products directly, the analysis includes photodetectors for scintillator arrays. Beyond present technology we also examine currently evolving structures and techniques which show potential for producing practical devices in the foreseeable future.
Date: November 1, 1984
Creator: Spieler, H.G. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

Electrical properties of dislocations in ultra-pure germanium

Description: Defect states due to grown-in dislocations in ultra-pure p-type germanium have been observed using Deep Level Transient Spectroscopy (DLTS) and Hall effect. These states are found to be composed of two bands of acceptor type levels whose energy and half width are influenced by both the presence of hydrogen and the crystal growth direction. At a net acceptor concentration of 10/sup 10/cm/sup -3/ a threshold dislocation density of approx. 10/sup 4/cm/sup -2/ is required for the observation of dislocation bands.
Date: June 1, 1979
Creator: Hubbard, G.S. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

High-resolution EPR and piezospectroscopy studies of the lithium-oxygen donor in germanium

Description: Lithium-oxygen donors in germanium were studied at low concentration (< 10/sup 14/ cm/sup -3/) by means of Electron Paramagnetic Resonance and Photoelectric Piezospectroscopy. We find unambiguously four equivalent real-space positions with <111> symmetry, which together with the four-valley conduction band lead to a 16-fold ground state. The system exhibits dynamic tunneling between the four equivalent orientations.
Date: September 1, 1978
Creator: Haller, E.E. & Falicov, L.M.
Partner: UNT Libraries Government Documents Department

Impurity complex formation in ultra-pure germanium

Description: Several unknown, hydrogenic acceptors and donors were recently discovered in ultra-pure germanium by photoelectric spectroscopy. These centers are not created by elemental impurities. Comparative analysis of a large number of crystals grown under various conditions lead to the conclusion that copper, a fast diffusing multivalent acceptor, together with lithium and/or hydrogen, is responsible for several of the unknown centers. This is the first time that hydrogen has been recognized as playing the role of a donor pairing with an acceptor. Hall effect measurements complementing the photoelectric spectroscopy results lead to a tentative assignment of the following energy levels: (Cu, Li) complexes: E/sub V/ + 20.5 meV/super */, E/sub V/ + 25.0 meV/super */, E/sub V/ + 275 meV(/super */hydrogenic acceptor); (Cu, H) complexes: E/sub V/ + 17.0 meV/super */, E/sub V/ + 17.5 meV/super */, E/sub V/ + 175 meV. Experiments which may help determine the structure of the complexes are proposed.
Date: May 1, 1977
Creator: Haller, E. E. & Hubbard, G. S.
Partner: UNT Libraries Government Documents Department

Applications of Heavy-Ion Rutherford Backscattering Spectrometry (HIRBS) to the analysis of contact structures on GaAs and Ge

Description: The use of Heavy-Ion Rutherford Backscattering Spectrometry (HIRBS) for the analysis of layered structures on GaAs and Ge substrates has been studied. Direct comparisons of data obtained using both /sup 16/O and /sup 4/He projectiles for the characterization of contact structures have demonstrated the advantages of HIRBS for the study of substrates with increased atomic masses due to the improved mass resolution of the method for high Z materials. We present results obtained from a study of thermally induced interactions between Ga As and Ge substrates and the metals Pt and Pd. Results of the analysis of multiple layered structures on GaAs and GaAlAs substrate with HIRBS are also discussed.
Date: September 1, 1984
Creator: Yu, K.M.; Jaklevic, J.M. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

Development of high responsivity Ge:Ga photoconductors

Description: Czochralski-grown gallium-doped germanium (Ge:Ga) single crystal samples with a compensation of 10/sup -4/ have been modified by the indiffusion of Cu to produce photoconductors which provide NEPs comparable to current optimum Ge:Ga detectors, but exhibit responsivities a factor of 5 to 6 times higher when tested at a background photon flux of 10/sup 8/ photons/sec at lambda=93 ..mu..m. The introduction of Cu, a triple acceptor in Ge which acts as a neutral scattering center, reduces carrier mobility and extends the breakdown field significantly in this ultra-low compensation material.
Date: June 1, 1984
Creator: Haegel, N.M.; Hueschen, M.R. & Haller, E.E.
Partner: UNT Libraries Government Documents Department

Effect of crystal growth direction on the energy resolution of high-purity germanium detectors

Description: (100) and (113) direction high-purity germanium crystals with dislocation densities > 10/sup 4/ cm/sup -2/ have been examined by Hall effect, Deep Level Transient Spectroscopy and gamma-ray spectrometer performance. High dislocation density in (100) crystals appears to give rise to acceptor levels which cause broadened and/or asymmetric photopeaks. (113) crystals with EPD > 10/sup 4/cm/sup -2/ do not show these effects.
Date: October 1, 1978
Creator: Hubbard, G.S.; Haller, E.E. & Hansen, W.L.
Partner: UNT Libraries Government Documents Department

Status of NTD Ge bolometer material and devices

Description: This status report is a direct follow-up to the presentation given at the first IR Detector Technology Workshop which took place at NASA Ames Research Center on July 12 and 13, 1983. The conclusions which we presented at that meeting are still fully valid. In the meantime we have learned more about the physics of hopping conduction at very low temperatures which will be important for bolometer design and operation at ever decreasing temperatures. Resistivity measurements have been extended down to 50 mK. At such low temperatures, precise knowledge of the neutron capture cross sections sigma/sub n/ of the various Ge isotopes is critical if one is to make an accurate prediction of the dopant concentrations and compensation, and therefore resistivity, that will result from a given irradiation. We describe an empirical approach for obtaining the desired resistivity material and are in the process of conducting a set of experiments which will improve the knowledge of the effective sigma/sub n/ values for a given location in a particular reactor. A wider range of NTD Ge samples is now available. Noise measurements on bolometers with ion implanted contacts show that no 1/f noise component appears down to 1 Hz and probably lower. 4 refs., 5 figs.
Date: August 1, 1985
Creator: Haller, E.E.; Haegel, N.M. & Park, I.S.
Partner: UNT Libraries Government Documents Department

Hydrogen concentration and distribution in high-purity germanium crystals

Description: High-purity germanium crystals used for making nuclear radiation detectors are usually grown in a hydrogen ambient from a melt contained in a high-purity silica crucible. The benefits and problems encountered in using a hydrogen ambient are reviewed. A hydrogen concentration of about 2 x 10/sup 15/cm/sup -3/ has been determined by growing crystals in hydrogen spiked with tritium and counting the tritium ..beta..-decays in detectors made from these crystals. Annealing studies show that the hydrogen is strongly bound, either to defects or as H/sub 2/ with a dissociation energy > 3 eV. This is lowered to 1.8 eV when copper is present. Etching defects in dislocation-free crystals grown in hydrogen have been found by etch stripping to have a density of about 1 x 10/sup 7/ cm/sup -3/ and are estimated to contain 10/sup 8/ H atoms each.
Date: October 1, 1981
Creator: Hansen, W.L.; Haller, E.E. & Luke, P.N.
Partner: UNT Libraries Government Documents Department

Zone refining high-purity germanium

Description: The effects of various parameters on germanium purification by zone refining have been examined. These parameters include the germanium container and container coatings, ambient gas and other operating conditions. Four methods of refining are presented which reproducibly yield 3.5 kg germanium ingots from which high purity (vertical barN/sub A/ - N/sub D/vertical bar less than or equal to2 x 10/sup 10/ cm/sup -3/) single crystals can be grown. A qualitative model involving binary and ternary complexes of Si, O, B, and Al is shown to account for the behavior of impurities at these low concentrations.
Date: October 1, 1977
Creator: Hubbard, G.S.; Haller, E.E. & Hansen, W.L.
Partner: UNT Libraries Government Documents Department

Liquid-helium scintillation detection with germanium photodiodes

Description: Special high-purity germanium photodiodes have been developed for the direct detection of vacuum ultraviolet scintillations in liquid helium. The photodiodes are immersed in the liquid helium, and scintillations are detected through one of the bare sides of the photodiodes. Test results with scintillation photons produced by 5.3-MeV ..cap alpha.. particles are presented. The use of these photodiodes as liquid-helium scintillation detectors may offer substantial improvements over the alternate detection method requiring the use of wavelength shifters and photomultiplier tubes.
Date: May 1, 1982
Creator: Luke, P.N.; Haller, E.E. & Steiner, H.M.
Partner: UNT Libraries Government Documents Department

Neutron-transmutation-doped germanium bolometers

Description: Six slices of ultra-pure germanium were irradiated with thermal neutron fluences between 7.5 x 10/sup 16/ and 1.88 x 10/sup 18/ cm/sup -2/. After thermal annealing the resistivity was measured down to low temperatures (< 4.2 K) and found to follow the relationship rho - rho/sub 0/exp(..delta../T) in the hopping conduction regime. Also, several junction FETs were tested for noise performance at room temperature and in an insulating housing in a 4.2K cryostat. These FETs will be used as first stage amplifiers for neutron-transmutation-doped germanium bolometers.
Date: February 1, 1983
Creator: Palaio, N.P.; Rodder, M.; Haller, E.E. & Kreysa, E.
Partner: UNT Libraries Government Documents Department

Protective surface coatings on semiconductor nuclear radiation detectors

Description: Surface states on germanium p-i-n junctions have been investigated using deep level transient spectroscopy (DLTS) and collimated beams of 60 keV gamma-rays. The DLTS spectra have a characteristic signature for each surface treatment but the spectra are complex and not readily interpretable as to suitability for radiation detectors. Collimated gamma-ray beams give a direct measure of surface channel effects and typeness. Hydrogenated amorphous germanium (a-Ge:H) was explored as a surface layer to adjust the electrical state and passivate the surface. Our measurements show that these layers produce flat band conditions, introduce no additional noise and appear to be stable against a variety of ambients.
Date: October 1, 1979
Creator: Hansen, W.L.; Haller, E.E. & Hubbard, G.S.
Partner: UNT Libraries Government Documents Department