NASA Technical Reports Server (NTRS) 20110014685: Doping-Induced Interband Gain in InAs/AlSb Quantum Wells

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by  NASA Technical Reports Server (NTRS)

Books & Reports
electrons and holes, thereby leading to the data falling past the end of the
Large Fluvial Fans and weak interband dipole matrix elements. range window, there is obtained a noise
Exploration In the doping schemes studied, an inte- baseline that is used to calculate a
for Hydrocarbons rior sublayer of each AlSb layer was threshold value for each filter. The data
A report discusses the geological doped at various total areal densities up from each filter is analyzed by a com-
phenomena known, variously, as mod- to 5 × 1012 cm–2. It was found that (1) plex weighting scheme and the filter
ern large (or large modern) fluvial proper doping converts the InAs layer with the greatest weight is selected. A
fans or large continental fans, from a from a barrier to a well for holes, region around the peak of the ground-
perspective of exploring for hydrocar- thereby converting the heterostructure return pulse associated with the selected
bons. These fans are partial cones of from type II to type I; (2) the resultant filter is placed in telemetry, as well as in-
river sediment that spread out to radii dipole matrix elements and interband formation on its location, height, and
of 100 km or more. Heretofore, they gains are comparable to those of typical other characteristics. The software re-
have not been much recognized in the type-I heterostructures; and (3) dipole quires many uplinked parameters as
geological literature — probably be- moments and optical gain increase with input. Included in the report is a discus-
cause they are difficult to see from the the doping level. Optical gains in the sion of major software-development
ground. They can, however, be seen in transverse magnetic mode can be almost problems posed by the design of the FIR
photographs taken by astronauts and ten times those of other semiconductor chip and the need for the software to
on other remotely sensed imagery. material systems in devices used to complete its process within 20 ms to fit
Among the topics discussed in the re- generate medium-wavelength infrared within the overall 25-ms cycle.
port is the need for research to under- (MWIR) radiation. Hence, doped This work was done by Jacob S. Rosenberg
stand what seems to be an association InAs/AlSb QWs could be the basis of an and Carlos Trujillo of Goddard Space
among fluvial fans, alluvial fans, and alternative material system for devices to Flight Center. Further information is con-
hydrocarbon deposits. Included in the generate MWIR radiation. tained in a TSP (see page 1).
report is an abstract that summarizes This work was done by K. I. Kolokolov and GSC-14382
the global distribution of large mod- C. Z. Ning of Ames Research Center. Fur-
ern fluvial fans and a proposal to use ther information is contained in a TSP (see
that distribution as a guide to under- page 1).
standing paleo-fluvial reservoir systems Inquiries concerning rights for the com- Upgrading the Space Shuttle
where oil and gas have formed. Also in- mercial use of this invention should be ad- Caution and Warning System
cluded is an abstract that summarizes dressed to the Patent Counsel, Ames Research A report describes the history and
what a continuing mapping project Center, (650) 604-5104. Refer to ARC- the continuing evolution of an avionic
has thus far revealed about the charac- 15157-1 system aboard the space shuttle, de-
teristics of large fans that have been noted the caution and warning system,
found in a variety of geological envi- that generates visual and auditory dis-
ronments. plays to alert astronauts to malfunc-
This work was done by Murray Justin Development of Software for tions. The report focuses mainly on
Wilkinson of Lockheed Martin Corp. for a Lidar-Altimeter Processor planned human-factors-oriented up-
Johnson Space Center. A report describes the development grades of an alphanumeric fault-sum-
This invention is owned by NASA, and a of software for a digital processor that mary display generated by the system.
patent application has been filed. Inquiries operates in conjunction with a finite-im- Such upgrades are needed because the
concerning nonexclusive or exclusive license pulse-response (FIR) chip in a space- display often becomes cluttered with
for its commercial development should be ad- borne lidar altimeter. Processing is extraneous messages that contribute to
dressed to the Patent Counsel, Johnson Space started by a laser-fire interrupt signal the difficulty of diagnosing malfunc-
Center, (281) 483-0837. Refer to MSC- that is repeated at intervals of 25 ms. tions. In the first of two planned up-
23424. For the purpose of discriminating be- grades, the fault-summary display will
tween returns from the ground and re- be rebuilt with a more logical task-ori-
turns from such things as trees, build- ented graphical layout and multiple
ings, and clouds, the software is text fields for malfunction messages. In
Doping-Induced Interband required to scan digitized lidar-return the second upgrade, information dis-
Gain in InAs/AlSb Quantum data in reverse of the acquisition se- played will be changed, such that text
Wells quence in order to distinguish the last fields will indicate only the sources
A paper describes a computational return pulse from within a commanded (that is, root causes) of malfunctions;
study of effects of doping in a quantum ground-return range window. The digi- messages that are not operationally use-
well (QW) comprising a 10-nm-thick tized waveform information within this ful will no longer appear on the dis-
layer of InAs sandwiched between two range window is filtered through 6 plays. These and other aspects of the
21-nm-thick AlSb layers. Heretofore, matched filters, in the hardware elec- upgrades are based on extensive collab-
InAs/AlSb QWs have not been useful as tronics, in order to maximize the proba- oration among astronauts, engineers,
interband gain devices because they bility of finding echoes from sloped or and human-factors scientists. The re-
have type-II energy-band-edge align- rough terrain and minimize the proba- port describes the human-factors prin-
ment, which causes spatial separation of bility of selecting cloud returns. From ciples applied in the upgrades.
NASA Tech Briefs, January 2005 33