Electro-Optics - Applied Optics Fundamentals and Device Applications - page 46

of 200 μm, and finally, a method for achieving electrical and optical confine-
ment in the lateral dimension.

2.5.10 Integrated Device Developments

There have been a number of demonstrations of laser diodes integrated with
either a single or a few GaAs IC components [67]. For the past several years, a
number of companies, including Honeywell and Rockwell, have been devel-
oping technology to integrate optoelectronic devices with complex GaAs cir-
cuits [68]. One structure that has been demonstrated [69] is shown in Figure
2.27. The components in the structure are a transverse junction stripe (TJS)
laser, a FET driver, and a 4:1 MUX. The MUX and driver active regions are
formed by selective ion implantation into the semi-insulating GaAs substrate,
while the TJS laser is fabricated by liquid phase epitaxial growth in a well
etched into the substrate. The rear laser mirror facet is formed with a micro-
cleave process developed at the California Institute of Technology, CA [70]. A
cross-sectional view of the microcleave process is shown in Figure 2.28. The
small horseshoe-shaped wing at the end of the laser is formed by chemically
etching under the Al-facet. The wing is broken off to form a smooth cleaved
mirror facet. Measurements have shown that lasers with undercut mirrors
have operating characteristics (laser threshold 37 mA) identical to similar

4:1
Multiplexer

Buffer

Counter

FET
laser
driver

Processed
laser mirror

Integrated
laser
structure

N

Clock
Clear

Input 1
Input 2
Input 3
Input 4

Semi-insulating
GaAs substrate

Buffer

FIGURE 2.27
Block diagram of the monolithic optoelectronic transmitter consisting of an integratable TJS
Laser, a laser driver, and a 4:1 MUX.