Integrated Optics - Applied Optics Fundamentals and Device Applications - page 263

Effusion
oven

Main shutter
Rotating substrate
holder

Ga

Gate valve

As

Al

Sample exchange
load lock

Dopant

Effusion
oven shutters

To variable speed
motor and substrate
heater supply

FIGURE 5.27
A typical MBE system for growth of AlGaAs.

surfaces allow complex doping and compositional structures and synthesis
of artificial materials with prescribed characteristics.
Characterization of MBE samples occurs first during growth with the in
situ capability of RHEED and Auger electron spectroscopy which provide
information for growth conditions, allowing preparation of high quality
samples. After growth of samples, x-ray diffraction and electron microscopy
provide information on crystal structure, crystal orientation, and crystal
perfection. Transport measurements provide information concerning carrier
concentration and mobility. Raman spectroscopy can provide information
regarding the quality of interfaces.
Complex optical circuit structures require epitaxial layer uniformity and
precision in thickness, doping, and AlGaAs composition. Depending upon
the particular design, there are advantages to both MOCVD and MBE. Tables
at Figures 5.28 and 5.29 compare material properties, parameter controls, and
system cost for the two techniques.

5.10.5 MBE Development in Space

Past and present experience in submicron optoelectronic and electronic
devices employing single crystal GaAs in epitaxial interface with single crys-
tal AlGaAs has clearly indicated that the limiting criteria for optimal device
performance is the purity of the AlGaAs. Even under the best starting condi-
tion vacuums available on earth (10 −11 -10 −12 Torr), there exist serious defects
caused by impurity atoms and by water vapor as well as Co 2 and O 2 . Such