Integrated Optics - Applied Optics Fundamentals and Device Applications - page 262

Mass flow controllers

Exhaust

AsH 3 in H 2

H 2 Se in H 2

Substrate
rf

Power DEZ

Susceptor TMGa

Q uartz
reactor

TMAl

Purified H 2

Vacuum

Constant-temperature
baths

Air-operated
valves

FIGURE 5.26
Vertical atmospheric-pressure MOCVD reactor.

wafers in a single processing cycle and up to three processing cycles may be
completed in a production shift.
The aluminum composition ( x ) of the alloy is determined from the peak
energy of the band-edge emission of photoluminescence spectra for single
layers. A special facility can profile the photovoltage of a multilayer structure
at the same time that a carrier profile is obtained by electrolytic removal of
material in conjunction with computer controlled capacitance-voltage deter-
minations. Deep level traps in the material are investigated by the Deep
Level Trap Spectroscopy (DLTS) technique and other related measurements.

5.10.4 MBE: Growth and Evaluation

Molecular beam epitaxy, which involves the reaction of one or more thermal
beams of the desired atoms or molecules with a crystalline substrate under
ultrahigh vacuum conditions (10 −10 -10 −11 Torr background, 10 −6 Torr operat-
ing pressure), can achieve precise control in chemical compositions, doping
profiles, and layer thickness. A typical MBE system for growth of GaAlAs is
shown in Figure 5.27. Uniformity of chemical composition and doping pro-
file are typically better than 1% with thickness variations less than +0.5%.
An additional advantage is that no high temperature processes are required,
so that very minimal bulk diffusion effects occur. Single-crystal multilayer
AlGaAs atomic layers can be grown by MBE. Atomically smooth growth