INSTABILITIES IN THE POWER SPECTRUM OF MODE-LOCKED SEMICONDUCTOR LASERS

In the past few years on-line digital television frame store devices coupled to computers have been employed to attempt to measure the microscope parameters of defocus and astigmatism. The ultimate goal of such tasks is to fully adjust the operating parameters of the microscope and obtain an optimum image for viewing in terms of its information content. The initial approach to this problem, for high resolution TEM imaging, was to obtain the power spectrum from the Fourier transform of an image, find the contrast transfer function oscillation maxima, and subsequently correct the image. This technique requires a fast computer, a direct memory access device and even an array processor to accomplish these tasks on limited size arrays in a few seconds per image. It is not clear that the power spectrum could be used for more than defocus correction since the correction of astigmatism is a formidable problem of pattern recognition.

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Structural aspects of silicon diffusion in quaternary III-V thin-film semiconductors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100088567 ◽

1991 ◽

Vol 49 ◽

pp. 850-851

Author(s):

F. A. Ponce ◽

R. L. Thornton ◽

G. B. Anderson

Keyword(s):

Semiconductor Lasers ◽

Wide Bandgap ◽

Semiconductor Diode ◽

Visible Range ◽

P System ◽

Misfit Dislocations ◽

Lattice Match ◽

Semiconductor Diode Laser ◽

Thin Film Semiconductors ◽

Silicon Diffusion

The InGaAlP quaternary system allows the production of semiconductor lasers emitting light in the visible range of the spectrum. Recent advances in the visible semiconductor diode laser art have established the viability of diode structures with emission wavelengths comparable to the He-Ne gas laser. There has been much interest in the growth of wide bandgap quaternary thin films on GaAs, a substrate most commonly used in optoelectronic applications. There is particular interest in compositions which are lattice matched to GaAs, thus avoiding misfit dislocations which can be detrimental to the lifetime of these materials. As observed in Figure 1, the (AlxGa1-x)0.5In0.5P system has a very close lattice match to GaAs and is favored for these applications.In this work, we have studied the effect of silicon diffusion in GaAs/InGaAlP structures. Silicon diffusion in III-V semiconductor alloys has been found to have an disordering effect which is associated with removal of fine structures introduced during growth. Due to the variety of species available for interdiffusion, the disordering effect of silicon can have severe consequences on the lattice match at GaAs/InGaAlP interfaces.

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Strain measurement in In0.2Ga0.8As/GaAs quantum wires by convergent beam electron diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138592 ◽

1995 ◽

Vol 53 ◽

pp. 444-445

Author(s):

S. Hillyard ◽

Y.-P. Chen ◽

J.D. Reed ◽

W.J. Schaff ◽

L.F. Eastman ◽

...

Keyword(s):

Electron Diffraction ◽

Semiconductor Lasers ◽

Quantum Wire ◽

Quantum Wires ◽

Convergent Beam Electron Diffraction ◽

Zero Order ◽

Beam Electron ◽

Local Lattice ◽

Device Applications ◽

Convergent Beam

The positions of high-order Laue zone (HOLZ) lines in the zero order disc of convergent beam electron diffraction (CBED) patterns are extremely sensitive to local lattice parameters. With proper care, these can be measured to a level of one part in 104 in nanometer sized areas. Recent upgrades to the Cornell UHV STEM have made energy filtered CBED possible with a slow scan CCD, and this technique has been applied to the measurement of strain in In0.2Ga0.8 As wires.Semiconductor quantum wire structures have attracted much interest for potential device applications. For example, semiconductor lasers with quantum wires should exhibit an improvement in performance over quantum well counterparts. Strained quantum wires are expected to have even better performance. However, not much is known about the true behavior of strain in actual structures, a parameter critical to their performance.

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Log-log scale roughness spectroscopy of surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100146965 ◽

1993 ◽

Vol 51 ◽

pp. 224-225

Author(s):

P. Fraundorf ◽

B. Armbruster

Keyword(s):

Power Spectrum ◽

Autocorrelation Function ◽

Power Spectra ◽

Scanning Force Microscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Scanning Force ◽

Lateral Structure ◽

Scale Roughness

Optical interferometry, confocal light microscopy, stereopair scanning electron microscopy, scanning tunneling microscopy, and scanning force microscopy, can produce topographic images of surfaces on size scales reaching from centimeters to Angstroms. Second moment (height variance) statistics of surface topography can be very helpful in quantifying “visually suggested” differences from one surface to the next. The two most common methods for displaying this information are the Fourier power spectrum and its direct space transform, the autocorrelation function or interferogram. Unfortunately, for a surface exhibiting lateral structure over several orders of magnitude in size, both the power spectrum and the autocorrelation function will find most of the information they contain pressed into the plot’s origin. This suggests that we plot power in units of LOG(frequency)≡-LOG(period), but rather than add this logarithmic constraint as another element of abstraction to the analysis of power spectra, we further recommend a shift in paradigm.

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{10} edge dislocations in YSZ films grown on (100)MgO by PLD

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100170384 ◽

1994 ◽

Vol 52 ◽

pp. 530-531

Author(s):

Jason R. Heffelfinger ◽

C. Barry Carter

Keyword(s):

Thin Films ◽

Semiconductor Lasers ◽

Vapor Deposition ◽

Substrate Surface ◽

Laser System ◽

Average Energy ◽

Target Material ◽

Chemical Vapor ◽

Buffer Layers ◽

Organic Chemical

Yttria-stabilized zirconia (YSZ) is currently used in a variety of applications including oxygen sensors, fuel cells, coatings for semiconductor lasers, and buffer layers for high-temperature superconducting films. Thin films of YSZ have been grown by metal-organic chemical vapor deposition, electrochemical vapor deposition, pulse-laser deposition (PLD), electron-beam evaporation, and sputtering. In this investigation, PLD was used to grow thin films of YSZ on (100) MgO substrates. This system proves to be an interesting example of relationships between interfaces and extrinsic dislocations in thin films of YSZ.In this experiment, a freshly cleaved (100) MgO substrate surface was prepared for deposition by cleaving a lmm-thick slice from a single-crystal MgO cube. The YSZ target material which contained 10mol% yttria was prepared from powders and sintered to 85% of theoretical density. The laser system used for the depositions was a Lambda Physik 210i excimer laser operating with KrF (λ=248nm, 1Hz repetition rate, average energy per pulse of 100mJ).

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