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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

An introduction to blocked impurity band detectors

Blocked impurity band detectors fabricated using standard silicon technologies offer the possibility of combining high sensitivity and high accuracy in a single detector operating in a low background environment. The solid state photomultiplier described by Petroff et al., which is a new type of blocked impurity band detector, offers even higher sensitivity as well as operation in the visible spectral region. The principle of operation and possible application of blocked impurity band detectors for stellar seismology and the search for extra-solar planets are described.

Geist, Jon↗
NASA NTRS1989

Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays

Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds.

Herter, T.↗
NASA NTRS1993

Germanium blocked-impurity-band detector arrays - Unpassivated devices with bulk substrates

We have fabricated and characterized six-element monolithic arrays of Ge:Ga blocked-impurity-band detectors, with threshold wavelength 220 microns, peak quantum efficiency 14 percent, detective quantum efficiency 9 percent, dark current 300 e(-)/s, and response uniformity better than 4 percent. The devices are described very well by the standard model of blocked-impurity-band detectors and appear to satisfy many of the requirements of low-background astronomical instruments.

Watson, Dan M.↗
NASA NTRS1989

Blocked impurity band hybrid infrared focal plane arrays for astronomy

High-performance infrared hybrid focal plane arrays using 10- x 50-element Si:As blocked-impurity-band (BIB) detectors (cutoff wavelength = 28 microns) and matching switched MOSFET multiplexers have been developed and characterized for space astronomy. Use of impurity-band-conduction technology provides detectors which are nuclear-radiation-hard and free of the many anomalies associated with conventional silicon photoconductive detectors. Emphasis in the present work is on recent advances in detector material quality which have led to significantly improved detector and hybrid characteristics. Results demonstrating increased quantum efficiency (particularly at short-wavelength infrared), obtained by varying the BIB detector properties (infrared active layer thickness and arsenic doping profile), are summarized. Measured read noise and dark current for different temperatures are reported. The hybrid array performance achieved demonstrates that BIB detectors are well suited for use in astronomical instrumentation.

Reynolds, D. B.↗
NASA NTRS1990

Status of the NOAO evaluation of the Hughes 20x64 Si:As impurity band conduction array

The Hughes 20 x 64 Si:As impurity band conduction arrays designed for ground-based and spaceborne astronomy observations is described together with experiments performed at NOAO to test these arrays. Special attention is given to the design and the characteristics of the test system and to the test methods. The initial tests on two columns of one array indicate that the array is easy to operate and performed satisfactorily.

Fowler, A. M.↗
NASA NTRS1989

Germanium Blocked Impurity Band (BIB) detectors

Information is given in viewgraph form. The advantages of the Si blocked impurity band (BIB) detector invented by M. D. Petroff and M. G. Stabelbroek are noted: smaller detection volume leading to a reduction of cosmic ray interference, extended wavelength response because of dopant wavefunction overlap, and photoconductive gain of unity. It is argued that the stated advantages of Si BIB detectors should be realizable for Ge BIB detectors. Information is given on detector development, subtrate choice and preparation, wafer polising, epitaxy, characterization of epi layers, and preliminary Ge BIB detector test results.

Haller, E. E.↗
NASA NTRS1989

Tests of the Rockwell Si:As Back-Illuminated Blocked-Impurity Band (BIBIB) detectors

Two arrays of Rockwell's Si:As back-illuminated blocked-impurity-band detectors were tested at the Max-Planck-Institute for Astronomy (MPIA) at low background and low temperature for possible use in the astronomical space experiment ISOPHOT. For these measurements special test equipment was put together. A cryostat was mechanically modified to accommodate the arrays and special peripheral electronics was added to a microprocessor system to drive the cold multiplexer and to acquire the output data. The first device, a 16x50 element array on a fan-out board was used to test individual pixels with a trans-impedance-amplifier at a photon background of 10(exp 8) Ph s(-1)cm(-2) and at temperatures of 2.7 to 4.4 K. The noise-equivalent-power NEP is in the range 5 - 7 x 10(exp -18) WHz(exp -1/2), the responsivity is less than or equal to 100 AW(exp -1)(f = 10 Hz). The second device was a 10x50 array including a cold readout electronics of switched FETs (SWIFET). Measurements of this array were done in a background range of 5 x 10(exp 5) to 5 x 10(exp 11) Ph s(exp-1)cm(exp-2) and at operating temperatures between 3.0 and 4.8 K. The NEP ranges from less than 10(exp -18) at the lowest background to 2 x 10(exp -16) WHz(exp -1/2) at the highest flux.

Wolf, J.↗
NASA NTRS1993

Blocked impurity band detectors applied to tunable diode laser spectroscopy in the 8- to 28-micron range

A novel tunable diode laser spectrometer operating at 8-28 microns is described. A blocked impurity band Si:As chip is employed as detector. This device operates in this wavelength range with high detectivity and adequate frequency response for the high-sensitivity techniques used. A combination of sweep averaging and second-harmonic detection at 22 kHz yielded signal-to-noise ratios of 1200 at wavelengths above 20 microns. The sensitivity and spectral resolution achieved are an order of magnitude better than those of Fourier instruments in this range, with an improvement in instrument time response of about 3000. Several molecular bands of CO2 and N2O are observed for what is, to our knowledge, the first time with this instrument. Examples of spectral line measurements are presented.

Sirota, J. M.↗
NASA NTRS1975

Process-induced defects in terrestrial solar cells

Experimental and theoretical work on low resistivity, high efficiency solar cells indicates the dominant role that defects take in determining performance. High doping mechanisms produce gap shrinkage by band tailing, impurity band widening and impurity misfit; altered interband transmission rates result from Auger impact, SRH processes, or from electronic tunneling via defects. Characterizations of cell materials for their defects and their relations to the chosen fabrication processes are proposed.

Lindholm, F. A.↗
NASA NTRS1989

Alternating gradient photodetector

A far infrared (FIR) range responsive photodetector is disclosed. There is a substrate of degenerate germanium. A plurality of alternating impurity-band and high resistivity layers of germanium are disposed on the substrate. The impurity-band layers have a doping concentration therein sufficiently high to include donor bands which can release electrons upon impingement by FIR photons of energy hv greater than an energy gap epsilon. The high resistivity layers have a doping concentration therein sufficiently low as to not include conducting donor bands and are depleted of electrons. Metal contacts are provided for applying an electrical field across the substrate and the plurality of layers. In the preferred embodiment as shown, the substrate is degenerate n-type (N++) germanium; the impurity-band layers are n+ layers of germanium doped to approximately the low 10(exp 16)/cu cm range; and, the high resistivity layers are n-layers of germanium doped to a maximum of approximately 10(exp)/cu cm. Additionally, the impurity-band layers have a thickness less than a conduction-electron diffusion length in germanium and likely to be in the range of 0.1 to 1.0 micron, the plurality of impurity-bands is of a number such that the flux of FIR photons passing therethrough will be substantially totally absorbed therein, the thickness of the high resistivity layers is such compared to the voltage applied that the voltage drop in each the high resistivity layers controls the occurence of impact ionization in the impurity-band layers to a desired level.

Overhauser, Albert W.↗
NASA NTRS1991

Report of the direct infrared sensors panel

The direct infrared sensors panel considered a wide range of options for technologies relevant to the science goals of the Astrotech 21 mission set. Among the technologies assessed are: large format arrays; photon counting detectors; higher temperature 1 to 10 micro-m arrays; impurity band conduction (IBC) or blocked impurity band (BIB) detectors; readout electronics; and adapting the Space Infrared Telescope Facility and Hubble Space Telescope. Detailed development plans were presented for each of these technology areas.

Mccreight, Craig↗
NASA NTRS1993

Intensities and broadening coefficients for the Q branch of the 4nu-2 - nu-1 + nu-2 (471.511/cm) band of CO2

Absolute intensities for the Q-branch of the 4nu-2 - nu-1 + nu-1/2 (20,003-11,101) band in CO2 were measured for the first time. Measurements were performed for lines Q10 to Q28, at temperatures ranging from 385 to 426 K, for pressures from 3 to 40 torr, using our long wavelength tunable diode laser spectrometer. The combination of tunable diode lasers, a White cell, and a blocked impurity band detector made it possible to obtain signal to noise ratios greater than 1000 in the 471/cm spectral region, with about 3 x 10 exp -4/cm spectral resolution. The band strength was found to be 8.6(2) x 10 exp -25 cm/molec at 296 K, and the Hermann-Wallis factor was determined. Comparison with the values listed in the HITRAN 92 data base are presented. Self-, N2- and O2-broadening coefficients were also measured.

Sirota, J. M.↗
NASA NTRS1989

Extrinsic germanium Blocked Impurity Bank (BIB) detectors

Ge:Ga blocked-impurity-band (BIB) detectors with long wavelength thresholds greater than 190 microns and peak quantum efficiencies of 4 percent, at an operating temperature of 1.8 K, have been fabricated. These proof of concept devices consist of a high purity germanium blocking layer epitaxially grown on a Ga-doped Ge substrate. This demonstration of BIB behavior in germanium enables the development of far infrared detector arrays similar to the current silicon-based devices. Present efforts are focussed on improving the chemical vapor deposition process used to create the blocking layer and on the lithographic processing required to produce monolithic detector arrays in germanium. Approaches to test the impurity levels in both the blocking and active layers are considered.

Krabach, Timothy N.↗
NASA NTRS1986

Si:As BIB detector arrays

Highlights of the results obtained on arsenic-doped silicon blocked impurity band (BIB) detectors and arrays since the invention of the BIB concept a few years ago are presented. After a brief introduction and a description of the BIB concept, data will be given on single detector performance. Then different arrays that were fabricated will be described and test data presented.

Bharat, R.↗