Progress toward cascade cells made by OM-VPE

Organometallic Vapor Phase Epitaxy (COM-VPE) was used to make a sophisticated monolithic cascade cell, with a peak AMO efficiency of 16.6%, not corrected for 14% grid coverage. The cell has 9 epitaxial layers. The top cell is 1.35 microns thick with a 0.1 micron thich emitter. Both cells are heteroface n-p structures. The cascade cell uses metal interconnects. Details of growth and processing are described

Low‐temperature (10 K) photoluminescence of Ga1−xInxPyAs1−y quantum wells grown by metalorganic chemical vapor deposition

Ga1−x Inx As1−y Py /InP (x=0.72, y=0.39) lattice‐matched quantum wells (QWs) are grown by low‐pressure metalorganic chemical vapor deposition on (100) and 3° misoriented substrates, using different variations of growth technique. Low‐temperature (10 K) photoluminescence is used to characterize the QWs. We find that substrates oriented closely to (100) (no intentional misorientation) produce QWs of consistently higher quality as judged by the width of the n=1 photoluminescence peak. The use of growth interruptions at the well interfaces severely degrades the QW quality. The narrowest peak observed is 5.8 meV wide from a 70‐Å‐wide well.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70205/2/APPLAB-56-10-958-1.pd

Refractive index and electro‐optic effect in compressive and tensile strained quantum wells

The effects of biaxial compressive and tensile strain on the excitonic resonances and associated changes in refractive index and electro‐optic effect in quantum wells have been calculated and measured. Theoretical calculations include the important heavy‐hole–light–hole band mixing effects. It is seen that the excitonic contributions dominate near the band edge. With increasing compressive strain the linear electro‐optic effect is slightly increased, while the quadratic effect is greatly enhanced. The effects are reversed in quantum wells under tensile strain.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70690/2/JAPIAU-69-7-4071-1.pd

Structural study of GaSb/AlSb strained-layer superlattice

Owing to the lattice mismatch between GaSb and AlSb, a superlattice consisting of alternating layers of these materials will be strained. We have carried out ion-channeling measurements by backscattering of 1.76-MeV He ions, and present an experimental procedure and a data-analysis technique to measure the difference in strain between the two individual layers of the superlattice. The data analysis is based on computer simulations of channeling, the accuracy of which is supported by the many fine details of the experiments reproduced in the simulations. X-ray rocking-curve analysis yielded detailed profiles of strains in directions perpendicular and parallel to the surface. The x-ray value for the strain present at an unirradiated spot on the crystal is in excellent agreement with the value calculated by elasticity theory. In the bombarded region, the values of strain are less than the value calculated by elasticity theory. It appears that bombardment by the He ions reduced the strain by 50% and created lateral inhomogeneities in the crystal structure

World Wide Web Metaphors for Search Mission Data

A software program that searches and browses mission data emulates a Web browser, containing standard meta - phors for Web browsing. By taking advantage of back-end URLs, users may save and share search states. Also, since a Web interface is familiar to users, training time is reduced. Familiar back and forward buttons move through a local search history. A refresh/reload button regenerates a query, and loads in any new data. URLs can be constructed to save search results. Adding context to the current search is also handled through a familiar Web metaphor. The query is constructed by clicking on hyperlinks that represent new components to the search query. The selection of a link appears to the user as a page change; the choice of links changes to represent the updated search and the results are filtered by the new criteria. Selecting a navigation link changes the current query and also the URL that is associated with it. The back button can be used to return to the previous search state. This software is part of the MSLICE release, which was written in Java. It will run on any current Windows, Macintosh, or Linux system

Extensible Infrastructure for Browsing and Searching Abstracted Spacecraft Data

A computer program has been developed to provide a common interface for all space mission data, and allows different types of data to be displayed in the same context. This software provides an infrastructure for representing any type of mission data

Electro-optic effect in strained and lattice matched multiquantum well structures -- Role of excitonic resonances

The well known quantum confined Stark effect (QCSE) is currently being exploited to design optoelectronic devices based on electric field controlled absorption of photons. QCSE is also responsible for strong below exciton resonance changes in refractive index with applied field. These changes can be used for high speed couplers and switches in waveguides. This paper focuses on the use of strain to influence the excitonic resonances in InxGa1-xAs/Al0.2Ga0.8As and In0.53+/-xGa0.47[mnplus]xAs/InGaAsP multiple quantum wells. Experimental results are presented showing the effect of compressive and tensile strain on the refractive index changes. Theoretical results including the important HH-LH band mixing effects are presented for the electrooptic effect. In particular, the contribution of the excitonic part is discussed and is found to dominate the electro-optic effect near the bandedge.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28870/1/0000705.pd

High Power Edge-Emitting Light Emitting Diodes at 1.5µ with Extremely Low Back Facet Feedback

This paper describes novel semiconductor sources for optical low coherence reflectometry (OLCR), a measurement technique for characterizing device and fiber reflections with high sensitivity and high spatial resolution. Lasers and conventional superluminescent LEDs are not suitable for OLCR because strong reflections from the back facets mask weak reflection signals from the device or fiber under test. Even standard edge emitting LEDs (EELEDs) show significant reflections, which have limited the dynamic range of previous measurements. Low source output powers have also limited sensitivity. In order to obtain high power while minimizing internal reflections, a high single pass gain device is required. The record combination of high power and low internal reflections of the InGaAsP EELEDs reported here significantly expands the dynamic range and sensitivity of LED based reflectometry at 1.5 μm. This work also compares the characteristics of quantum well and bulk EELEDs