cet was 12.7 mW at 15 ° C. The inset of Fig. 4 shows the
laser spectrum with a central wavelength of 1490 nm.
On varying the Si waveguide width w, V
was found to
have a local minimum at w ⬃ 1.5
m, with dependence
shown in Fig. 5. This behavior can be understood qualita-
tively by considering the two limiting cases of waveguide
width. As width decreases, less of the mode resides in the
silicon, and thus experiences less feedback from the Si fac-
ets, which are of higher reﬂectivity than those in the III-V.
On the other hand, as width increases, the mode is less con-
ﬁned to the quantum well region and thus requires a higher
pump level to reach threshold. Further work on investigating
this effect and optimizing our gain structure to utilize the
relative strengths of these two regimes is underway.
We have shown how care in silicon processing steps for
hybrid systems can lead to good optical performance. Low
loss Si waveguides can be fabricated using resist reﬂow, low-
bias dry etching, and surface chemical treatments. Subse-
quent integration of these optical structures at low tempera-
ture is possible with plasma-assisted wafer bonding. By
using the CMOS compatible processes described, we can
integrate optics with electronics seamlessly without signiﬁ-
cantly altering the constraints on upstream processing steps
on the silicon. Further improvement is possible with super-
or new materials systems, and will make
this architecture even more attractive.
This work was supported by Defense Advanced Research
Projects Agency 共DARPA兲 Contract No. N66001-07-1-2058
and HR0011-04-1-0054, the U.S. Air Force Ofﬁce of Scien-
tiﬁc Research 共AFOSR兲 Grant No. FA9550-06-1-0480, and
the Center for Science and Engineering of Materials, a Na-
tional Science Foundation 共NSF兲 Materials Research Science
and Engineering Center at Caltech. The authors thank the
Kavli Nanoscience Institute, Caltech, for supporting fabrica-
tion. M.S. thanks the NSF Graduate Research Fellowship
program. A.Z. acknowledges postdoctoral fellowships from
the Center for the Physics of Information, Caltech, and the
Rothschild fellowship from Yad-Hanadiv Foundation, Israel.
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J. Vac. Sci. Technol. B, Vol. 27, No. 6, Nov/Dec 2009