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Haller, E. E.

Publications and source records attributed to Haller, E. E..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Infrared absorption study of neutron-transmutation-doped germanium

Using high-resolution far-infrared Fourier transform absorption spectroscopy and Hall effect measurements, the evolution of the shallow acceptor and donor impurity levels in germanium during and after the neutron transmutation doping process was studied. The results show unambiguously that the gallium acceptor level concentration equals the concentration of transmutated Ge-70 atoms during the whole process indicating that neither recoil during transmutation nor gallium-defect complex formation play significant roles. The arsenic donor levels appear at full concentration only after annealing for 1 h at 450 C. It is shown that this is due to donor-radiation-defect complex formation. Again, recoil does not play a significant role.

Park, I. S.↗
NASA NTRS1988

Germanium:gallium photoconductors for far infrared heterodyne detection

Highly compensated Ge:Ga photoconductors for high bandwidth heterodyne detection have been fabricated and evaluated. Bandwidths up to 60 MHz have been achieved with a corresponding current responsivity of 0.01 A/W. The expected dependence of bandwidth on bias field is obtained. It is noted that increased bandwidth is obtained at the price of greater required local oscillator power.

Park, I. S.↗
NASA NTRS1987

Stressed photoconductive detector for far-infrared space applications

An optimized leaf-spring apparatus for applying uniaxial stress to a Ge:Ga far-IR photoconductor has been designed and tested. This design has significant advantages for space applications which require high quantum efficiency and stable operation over long periods of time. The important features include adequate spring deflection with relatively small overall size, torque-free stress, easy measurement of applied stress, and a detector configuration with high responsivity. One-dimensional arrays of stressed photoconductors can be constructed using this design. A peak responsivity of 38 A/W is achieved in a detector with a cutoff wavelength of 200 microns, which was operated at a temperature of 2.0 K and a bias voltage equal to one-half of the breakdown voltage.

Wang, J.-Q.↗
NASA NTRS1986

Optical efficiency of far-infrared photoconductors

The present optimization of the geometry of far-IR photoconductive detectors with diffraction-limited throughput, on the basis of experimental and theoretical results, gives attention to the internal optical path relative to measured absorption length, photoconductive gain, uniformity of illumination, cosmic ray cross section, and design compatibility with the requirements of one- and two-dimensional arrays. It is demonstrated that a rod-shaped, square cross section detector geometry, having lateral face electrodes and a beveled backface with which to trap the radiation by total internal reflection, exhibits responsivity commensurate with that of the best available detectors in integrating cavities.

Wang, J.-Q.↗
NASA NTRS1986

Photo Hall-effect characterization of closely compensated Ge:Be

The temperature dependence of the free-carrier concentration in germanium doped with the double acceptor Be has been investigated using the photo Hall-effect technique and found to be strongly temperature dependent when the residual shallow impurities are closely compensated. Close compensation of shallow levels was achieved by controlling the concentration of a beryllium-hydrogen acceptor complex A(Be,H) which is present in crystals grown under a H2 atmosphere. This complex can be removed with high-temperature annealing. An increase of up to two orders of magnitude in free-carrier lifetime as a function of temperature is found to occur between 5 and 11 K in closely compensated material due to the population inversion of ionized centers created by optical pumping.

Germer, T. A.↗
NASA NTRS1986

Transient response of Ge:Be and Ge:Zn FIR photoconductors under low background photon flux conditions

An experimental study of the transient behavior of Ge:Be and Ge:Zn photoconductors to changes in photon flux rates has been performed under the low background flux conditions (10 to the 8th photon/s) typical of astronomy and astrophysics applications. A characteristic transient behavior with time constants ranging from 0.1 to greater than 5 s has been observed in both materials when the shallow levels are very closely compensated. The detector response consists of both a fast and a slow component. The amplitude of the slow component can be up to 10 times greater than the initial fast component. It has been established that this phenomenon cannot be explained by current models of carrier sweep-out or dielectric relaxation. The transient behavior has been characterized as a function of temperature, electric field, photoconductive gain and material parameters.

Haegel, N. M.↗
NASA NTRS1986

Ge:Be infrared photoconductors

Ge:Be photoconductors were optimized for the 30 to 50 micron wavelength range. Crystal growth of detector quality material requires good control of both the Be and residual impurity doping. Detective quantum efficiencies of n sub d = 46% at 5 A/W were achieved at a photon background of 10 to the 8th power p/s. The responsivity of Ge:Be detectors can be strongly temperature-dependent when the residual shallow levels in the material are closely compensated. Transient responses on the order of approximately 1 second were observed in some materials. The role of residual shallow impurities on the performance of photoconductors doped with semi-deep and deep impurities is discussed.

Haegel, N. M.↗
NASA NTRS1986

Status of NTD Ge bolometer material and devices

The first IR Detector Technology Workshop took place at NASA Ames Research Center on July 12 and 13, 1983. The conclusions presented at that meeting are still valid. More was learned 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 were 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. An empirical approach for obtaining the desired resistivity material is described and 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 is discussed. A wider range of NTD Ge samples is now available. Noise measurements on bolometers with ion implanted contacts show the no 1/f noise component appears down to 1 Hz and probably lower.

Haller, E. E.↗
NASA NTRS1985

Physics and design of advanced IR bolometers and photoconductors

The state-of-the-art in photoconductors and bolometers is reviewed, centering on the materials development and concepts of extrinsic Si and Ge devices. It is suggested that in the field of 2-D detector arrays the hybrid circuits containing a photoconductor or a photodiode array, bonded with In solder to a switched MOS readout device with up to 60 x 60 elements, will produce superior performance. Other systems discussed include charge-coupled devices, developed for visible-light imaging and adapted to IR imaging, and charge-injection devices, a monolithic combination of a standard photoconductor and a metal-insulator-semiconductor capacitor. Finally, it is pointed out that a nonequilibrium theory of bolometer noise demonstrates the possibility of reducing the traditionally accepted noise limits by 60 percent for Johnson noise and 30 percent for the noise from phonons in the thermal link of the bolometer.

Haller, E. E.↗
NASA NTRS1983

Neutron-transmutation-doped germanium bolometers

Six slices of ultra-pure germanium were irradiated with thermal neutron fluences between 7.5 x 10 to the 16th and 1.88 x 10 to the 18th per sq cm. After thermal annealing the resistivity was measured down to low temperatures (less than 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 4.2 K cryostat. These FETs will be used as first stage amplifiers for neutron-transmutation-doped germanium bolometers.

Palaio, N. P.↗
NASA NTRS1983

Performance and materials aspects of Ge:Be photoconductors

Ge:Be photoconductors have been developed for low photon background applications in the 30 - 50 micron wavelength region. These detectors provide higher responsivity and lower noise equivalent power (NEP) than the Ge:Ga detectors currently operating in this wavelength range. Beryllium-doped single crystals were grown by the Czochralski method from a carbon susceptor under a vacuum of approximately 10 to the -6th torr. An optimum detective quantum efficiency of 46 percent at a background flux of 1.5 x 10 to the 8th photons/second (7 x 10 to the -13th W is reported. Ge:Be detector performance is strongly influenced by the absolute concentrations and the concentration ratio of residual shallow donors and shallow acceptors.

Haegel, N. M.↗
NASA NTRS1983

Three holes bound to a double acceptor - Be(+) in germanium

A double acceptor binding three holes has been observed for the first time with photoconductive far-infrared spectroscopy in beryllium-doped germanium single crystals. This new center, Be(+), has a hole binding energy of about 5 meV and is only present when free holes are generated by ionization of either neutral shallow acceptors or neutral Be double acceptors. The Be(+) center thermally ionizes above 4 K. It disappears at a uniaxial stress higher than about a billion dyn/sq cm parallel to (111) as a result of the lifting of the valence-band degeneracy.

Haller, E. E.↗
NASA NTRS1983

Improved fabrication techniques for infrared bolometers

Ion implantation and sputter metallization are used to produce ohmic electrical contacts to Ge:Ga chips. The method is shown to give a high yield of small monolithic bolometers with very little low-frequency noise. It is noted that when one of the chips is used as the thermometric element of a composite bolometer it must be bonded to a dielectric substrate. The thermal resistance of the conventional epoxy bond is measured and found to be undesirably large. A procedure for soldering the chip to a metallized portion of the substrate in such a way as to reduce this resistance is outlined. An evaluation is made of the contribution of the metal film absorber to the heat capacity of a composite bolometer. It is found that the heat capacity of a NiCr absorber at 1.3 K can dominate the bolometer performance. A Bi absorber possesses significantly lower heat capacity. A low-temperature blackbody calibrator is built to measure the optical responsivity of bolometers. A composite bolometer system with a throughput of approximately 0.1 sr sq cm is constructed using the new techniques. The noise in this bolometer is white above 2.5 Hz and is slightly below the value predicted by thermodynamic equilibrium theory.

Lange, A. E.↗
NASA NTRS1983

Improved fabrication techniques for infrared bolometers

Techniques are described for producing improved infrared bolometers from doped germanium. Ion implantation and sputter metalization have been used to make ohmic electrical contacts to Ge:Ga chips. This method results in a high yield of small monolithic bolometers with very little low-frequency noise. When one of these chips is used as the thermometric element of a composite bolometer, it must be bonded to a dielectric substrate. The thermal resistance of the conventional epoxy bond has been measured and found to be undesirably large. A procedure for soldering the chip to a metalized portion of the substrate is described which reduced this resistance. The contribution of the metal film absorber to the heat capacity of a composite bolometer has been measured. The heat capacity of a NiCr absorber at 1.3 K can dominate the bolometer performance. A Bi absorber has significantly lower heat capacity. A low temperature blackbody calibrator has been built to measure the optical responsivity of bolometers. A composite bolometer system with a throughput of approx. 0.1 sr sq cm was constructed using the new techniques. In negligible background it has an optical NEP of 3.6 10((exp -15) W/sq root of Hz at 1.0 K with a time constant of 20 ms. The noise in this bolometer is white above 2.5 Hz and is somewhat below the value predicted by thermodynamic equilibrium theory. It is in agreement with calculations based on a recent nonequilibrium theory.

Lange, A. E.↗
NASA NTRS1983

Ge:Be far infrared photoconductors

Some conclusions reached are as follow. Ge:Be detectors provide lower Noise Equivalent Power (NEP) and higher responsivities than state of the art Ge:Ga detectors at 42 microns. Reliable Be doping was achieved with Czochralski growth from a carbon susceptor under vacuum. The photoconductive behavior of Ge:Be detectors is strongly influenced by the concentration of residual shallow impurities. Optimization of Ge:Be detectors requires both a low concentration and precise compensation of shallow acceptors.

Haegel, N. M.↗
NASA NTRS1983

Neutron transmutation doped Ge bolometers

Some conclusions reached are as follow. Neutron Transmutation Doping (NTD) of high quality Ge single crystals provides perfect control of doping concentration and uniformity. The resistivity can be tailored to any given bolometer operating temperature down to 0.1 K and probably lower. The excellent uniformity is advantaged for detector array development.

Haller, E. E.↗
NASA NTRS1983

Performance and materials aspects of Ge:Be photoconductors

Ge:Be photoconductors were developed for low photon background applications in the 30 to 50 MM wavelength region. These detectors provide higher responsivity and lower noise equivalent power (NEP) than the Ge:Ga detectors currently operating in this wavelength range. Beryllium doped single crystals were grown by the Czochralski method from a carbon susceptor under a vacuum of approx. one million torr. An optimum detective quantum efficiency of 46% at a background flux of 1.5 x 10 to the 8th power photons/second (7 x 10 to the 13th power W) was reported. Ge:Be detector performance is strongly influenced by the absolute concentrations and the concentration ratio of residual shallow donors and shallow acceptors.

Haegel, N. M.↗