Microstructure and interfacial properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As Page: 3 of 7
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EXPERIMENTAL
Layers containing 2%- and 8%-Ga
AlAs were laterally oxidized in a steam
furnace at 450*C by bubbling N2
through 80 C H20. The layers were *
part of working 980nm VCSEL
devices. TEM cross-sectional samples i
were made by dicing the devices out of
the wafer and epoxying them in a Si
support stack. The stack was
mechanically polished and then Ar-ion
thinned so that the unoxidized current
aperture of the device was thinned to
electron transparency (see Figure 1).
The final sample contained the oxide
terminus of the 2%-Ga AlAs layers that
define the current aperture in addition
to the 8%-Ga AIAs layers that formed
the remainder of the distributed Bragg Figure 2: A portion of a selected area diffraction pattern
reflector mirrors. The 8%-Ga layers of oxidized 2%Ga-AIAs. The image has been filtered to
onlyoxiize m nwar ascompred show detail. The sharp spots are from the unoxidized
only oxidize 8pm inward as compared GaAs layers, while the rings are from the oxidized layer.
to the 40pm oxidation of the 2%-Ga The d-spacing for each ring is indicated.
layers, due to the strong dependence of
oxidation rate on Ga content. TEM
images were obtained using 200keV electrons and recorded either directly on to film or using a
cooled, slow-scan video camera.
RESULTS
Figure 2 shows a portion of an
electron diffraction pattern which has
been high-pass filtered to show the
detail of the pattern. Clear
polycrystalline rings can be seen in the
pattern as well as an array of spots from -A
the surrounding GaAs layers, which act
as an internal calibration for the pattern.
By measuring the ring spacing, the
polycrystalline phase is identified as
A12039. This is the cubic phase of
Al203 and is based on the spinel A
(MgAI2O4) prototype with 32 O-atoms
forming an FCC sublattice, 8 Al-atoms
on the tetrahedral sites, and the
remaining 13 13 Al-atoms on the Figure 3: Dark-field g=(311) -A1203 image of oxidized
octahedral sites leaving 62/3 octahedral 8%-Ga AIAs. The bright grains are y-A1203 while the fine
vacancies . The degree of ordering of speckle between the grains is an amorphous phase.
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Twesten, R. D.; Follstaedt, D. M. & Choquette, K. D. Microstructure and interfacial properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As, article, December 31, 1996; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc676417/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.